Sprinkler Irrigation 2011 Complete

SPRINKLER IRRIGATION TECHNOLOGY AND APPLICATION Moshe Sne Irrigation and Plant Nutrition Consultant

2011

FOREWORD Ten years ago I had composed in cooperation with the late Elimelech Sapir the booklet “Sprinkler Irrigation”. The publication was used as a textbook in courses on irrigation organized by the Israeli Ministry of Foreign Affairs, The Centre for International Cooperation (Mashav), through its agricultural aegis The Centre for International Agricultural Development Cooperation (CINADCO), of the Israeli Ministry of Agriculture and Rural Development. The courses were carried-out in Israel and abroad for farmers, extension workers and policy makers in the field of irrigation and water management. They were designated for beginners and first time users of pressurized irrigation. Elucidation of the theoretical concepts was simplified to correspond with course participants' requirements. In the last decade, irrigation technologies became more advanced and more sophisicated, perceptions and attitudes were changed, so updating this publication had been essential. The booklet covers the technology and theory of sprinkler irrigation. In addition to conventional sprinkler irrigation, two derivative technologies are dealt – micro-irrigation and mechanized irrigation. Micro-irrigation employs micro emitters of low volume water discharge with two patterns of water distribution: a. Water is distributed through the air. b. Water is delivered directly to the soil from drippers and bubblers. The booklet relates only to those emitters that spread the water through the air, drippers and bubblers are excluded. The mechanized irrigation stemmed from sprinkler irrigation. In its first generation, the emitters were solely impact sprinklers. Later-on it shifted to using micro-emitters operating at low working pressure. This technology is gaining momentum all over the world. For that reason it is covered with much more detail than in the first edition. The manuscript emphasizes the practical aspects of sprinkler irrigation. The more advanced reader may refer to the extensive literature dealing with the subject. Related publications are listed in the References and Bibliography list at the end of the booklet. I have chosen to distribute the new publication by the Scribd network with the hope that users of the old version can update themselves. Moshe Sne

I

TABLE OF CONTENTS TOPIC

Page

Forword Table of Contents

I II

List of Tables List of Figures 1. INTRODUCTION Overview ………………………………………………………………….

IX XI 1 1

Surface Irrigation ………………………………………………………… Surface Irrigation Methods ……………………………………………..

2 2

Advanced Technologies ………………………………………………...

3

2. SPRINKLER IRRIGATION Introduction ………………………………………………………………. Advantages ………………………………………………………………..

4 4 4

Disadvantages and Limitations …………………………………………... Definitions ………………………………………………………………...

4 5

Nominal Pipe Diameter ………………………………………………… Sprinkler Types …………………………………………………………...

6 6

Sprinkler Classification …………………………………………………

7

The Jet Angle …………………………………………………………... Sprinkler Flow-rate …………………………………………………….. Working Pressure (Head) ……………………………………………….

13 14 14

Sprinkler Spacing, Selection and Operation …………………………...

14

3. MICRO-EMITTERS Introduction ………………………………………………………………. Micro-emitter types ……………………………………………………….

16 16

Static Micro-emitters (Micro-jets) ……………………………………...

17 17

Micro-sprinklers ………………………………………………………...

18

Micro-sprinkler Types ………………………………………………….

19

Emitter Mounting …………………………………………………………

20

Water Distribution Patterns ……………………………………………….

21

Pressure Compensation …………………………………………………...

22

II

4. THE IRRIGATION SYSTEM The Pumping Unit ………………………………………………………...

23 23

Pump Performance Terminology ……………………………………….

24

Pump Types ……………………………………………………………..

25

Suction Lift of a Pipe …………………………………………………...

26

Kinetic Pumps …………………………………………………………..

27

Installation of Vertical Turbine Pumps …………………………………

31

Submersible Pumps ……………………………………………………..

31

Pump Stages …………………………………………………………….

32

Solar water Pumps and Solar Water Pumping Systems ………………...

33

Variable speed drives …………………………………………………...

33

Selecting an Efficient Pumping Plant …………………………………..

34

Maintaining Irrigation System Efficiency ………………………………

34

The Pumping Unit Efficiency …………………………………………..

35

Cavitation ……………………………………………………………….

37

Pump Curves ……………………………………………………………

37

Pump and Well Testing …………………………………………………

39

5. PIPES AND ACCESSORIES Introduction ……………………………………………………………….

40 40

Pipe Materials ……………………………………………………………..

40

Iron, Steel and Copper …………………………………………………..

40

Aluminum ……………………………………………………………….

41

Asbestos-cement ………………………………………………………...

41

Concrete ………………………………………………………………...

41

Plastic Materials ………………………………………………………...

41

External and Internal Pipe Diameter ……………………………………...

45

6. COUPLERS Connectors (Fittings) ……………………………………………………...

46 46

Aluminum Couplers …………………………………………………….

46

7. REGULATION AND CONTROL Introduction ……………………………………………………………….

49 49

Supply Pipelines …………………………………………………………

49

III

The Control head ………………………………………………………….

49

Regulation and Control Devices ………………………………………….

50

Valves …………………………………………………………………..

50

Control Valves – Functioning and Actuation …………………………..

55

Check-valves ……………………………………………………………

58

Pressure Relief Valves ………………………………………………….

59

Pressure Regulators ……………………………………………………..

60

Air-release Valves ………………………………………………………

61

Atmospheric Vacuum Breakers ………………………………………...

62

Valve Capacity ……………………………………………………………

62

Automation ………………………………………………………………..

62

Overview ………………………………………………………………..

62

Flow-meters ……………………………………………………………..

63

Metering-valves (Hydrometers) ………………………………………...

64

Control Patterns …………………………………………………………

64

Irrigation Timers ………………………………………………………..

65

Computer-based Irrigation control Systems …………………………….

66

Supervisory Control And Data Acquisition (SCADA) ……………….. 8. WATER TREATMENT AND FILTRATION Introduction ……………………………………………………………….

68

Particulate Matter …………………………………………………………

71

Biological Substances …………………………………………………….

71

Chemical Precipitates ……………………………………………………..

72

Water hardness ……………………………………………………………

72

Iron and Manganese in Water …………………………………………..

73

Biological Oxidation Demand (BOD)……………………………………..

73

Filtration …………………………………………………………………..

73

Screen (Strainer) Filters ………………………………………………...

73

Disc Filters ……………………………………………………………...

75

Media Filters ……………………………………………………………

75

Sand Seperators …………………………………………………………

76

Filter Characteristics ……………………………………………………

77

IV

71 71

Flow Direction ………………………………………………………….

78

Filter Cleaning ………………………………………………………….

79

Filter Location …………………………………………………………..

81

Supplementary Water Treatments ………………………………………...

81

Chlorination ……………………………………………………………..

82

Acidification …………………………………………………………….

82

9. FERTIGATION Introduction ……………………………………………………………….

83 83

Advantages of fertigation ……………………………………………….

83

Limitations and Risks in Fertigation ……………………………………

83

Technologies of Fertigation ………………………………………………

83

Patterns of Injection …………………………………………………….

83

Fertilizer Tank …………………………………………………………..

84

Venturi Injector …………………………………………………………

85

Injection pumps …………………………………………………………

85

Injecton Site ………………………………………………………………

88

Injection at the Main Control Head ……………………………………..

88

Injection at Sub-main Heads ……………………………………………

88

Injection at the Control Head of each Block ……………………………

88

Control and Automation …………………………………………………..

88

Quantitative Dosing …………………………………………………….

88

Proprtional Dosing ……………………………………………………...

88

Avoiding Corrosion damage ……………………………………………...

89

Back-flow Prevention ……………………………………………………..

89

Back-siphonage …………………………………………………………

89

Back-pressure …………………………………………………………...

89

Chemical Aspects of fertigation …………………………………………..

89

Safety ……………………………………………………………………...

90

10. FLOW-RATE – WATER HEAD RELATIONSHIP Water Pressure …………………………………………………………….

91 91

Elevation Head (z) ………………………………………………………

91

Dynemic head ….. ………..…………………………………………….

92

V

Velocity Head …………………………………………………………...

92

Head Losses ………………………………………………………………

92

Friction Losses ………………………………………………………….

92

Operating Pressure ………………………………………………………..

96

Hydraulic Characteristics of Emitters …………………………………….

97

Calculation of Head Losses ……………………………………………….

98

Technical data …………………………………………………………….

98

Pressure measurement …………………………………………………..

98

Calculation of Longitudinal Head Losses ………………………………

98

11. WATER MOVEMENT AND DISTRIBUTION IN THE SOIL Soil Properties …………………………………………………………….

109 109

Soil Texture ……………………………………………………………..

109

Soil – Water relationship ………………………………………………….

111

Introduction ……………………………………………………………..

111

Saturation ……………………………………………………………….

111

Field Capacity

111

Wilting Point ……………………………………………………………

111

Factors affecting the Difference in Water Storage ……………………...

111

Available Water Capacity (AWC) ……………………………………...

112

Water Movement in the Soil ……………………………………………

112

The Determination of the Water Status in the Soil ……………………..

114

Water Intake Rate (WIR) of the Soil ……………………………………

115

Soil Wetting Patterns ……………………………………………………...

120

Water dosage ……………………………………………………………

120

Chemical Composition of the Water ……………………………………

120

Water Distribution Uniformity ……………………………………………

120

Distribution Uniformity in Fully Soil Surface Wetting Irrigation ……...

121

Distribution Uniformity in Localized irrigation ………………………..

129

12. SPRINKLER IRRIGATION TECHNIQUES Overview ………………………………………………………………….

131 131

Hand-move ………………………………………………………………..

131

Aluminum Pipes ………………………………………………………...

131

VI

Flexible laterals in Orchards ……………………………………………

133

Permanent Installations …………………………………………………...

134

Solid-set in Orchards ……………………………………………………

134

Mini-sprinklers Solid-set Systems in Vegetables ………………………

135

Mechanized Irrigation …………………………………………………….

137

Introduction ……………………………………………………………..

137

Towline …………………………………………………………………

137

Wheel Move …………………………………………………………….

138

Traveling Gun (Traveler) ……………………………………………….

141

Continuous-move Sprinkler System ………………………………………

147

The Water Emitters ……………………………………………………..

147

Center-Pivots ……………………………………………………………

157

Lineat-Move Systems …………………………………………………...

182

Control and Automation ………………………………………………...

187

13. PLANNING AND DESIGN OF SPRINKLER IRRIGATION Introduction ……………………………………………………………….

192 192

Planning …………………………………………………………………...

192

Soil Properties …………………………………………………………..

192

Climate Data …………………………………………………………….

194

Cropping Data …………………………………………………………..

194

Water Resources ………………………………………………………...

194

Data Manipulation ………………………………………………………...

195

Soil Wetting Pattern …………………………………………………….

195

Manipulation Steps ……………………………………………………...

196

Existing Equipment ……………………………………………………….

198

Calculation Formulae ……………………………………………………..

200

The Design Procedure …………………………………………………….

201

Overview ………………………………………………………………..

201

System Layout …………………………………………………………..

201

Water Flow Velocity ……………………………………………………

203

Spacing ………………………………………………………………….

203

Choosing Emitters and Laterals ………………………………………...

204

VII

Fxample of the Design Process …………………………………………...

204

Additional Examples of System Design Schemes ………………………..

209

14. IRRIGATION SCHEDULING Introduction ……………………………………………………………….

212 212

Calculation of the Water Amount in Sprinkler Irrigation ………………...

213

Calculation of the Precipitation Rate …………………………………...

213

Calculation of the Irrigation Duration …………………………………..

213

The Total Flow-rate of the Irrigated Area ………………………………

213

Scheduling with the water Budget Concept …………………………….

214

Scheduling Software and On-line Calculators ………………………….

216

15. MONITORING AND CONTROL Monitoring ………………………………………………………………...

219 219

Soil Water Monitoring ………………………………………………….

219

Plant Water Status Monitoring ………………………………………….

220

Plant Organs Elongation and Expansion ………………………………..

221

Irrigation Control …………………………………………………………

221

Manual Control …………………………………………………………

221

Quantitative Automatic Water Shutdown ………………………………

221

Fully Controlled Irrigation ……………………………………………...

221

Integrated Irrigation and Fertigation Control …………………………...

221

Integrated monitoring and Control ……………………………………...

222

16. MAINTENANCE Introduction ……………………………………………………………….

223 223

Installation ………………………………………………………………...

223

Mains and Sub-mains …………………………………………………...

223

Laterals ………………………………………………………………….

223

Routine Inspection ………………………………………………………..

224

Pump Inspection ………………………………………………………...

224

System Performance …………………………………………………….

224

Routine Maintenance ……………………………………………………...

225

System Flushing and Cleaning ………………………………………….

225

The Control Head ……………………………………………………….

225

VIII

The Irrigation Network ………………………………………………….

226

Micro-irrigation Systems ……………………………………………….

228

Mintenance of Accessories ……………………………………………...

228

Maintenance of Fertigation Systems ……………………………………

230

Chemical Water Treatments ………………………………………………

230

Acidification …………………………………………………………….

230

Oxidation ………………………………………………………………..

231

Overwintering of the Irrigation System …………………………………..

231

Entire System …………………………………………………………...

231

Filtration Equipment ……………………………………………………

231

Valves …………………………………………………………………...

231

Controllers and Sensors …………………………………………………

231

Chemical Injection Equipment ………………………………………….

231

Pumps …………………………………………………………………...

232

Electric Motors ………………………………………………………….

232

17. GLOSSARY

233

18. REFERENCES AND BIBLIOGRAPHY

262

LIST OF TABLES No.

PAGE

2.1. Wind Velocity Definitions …………………………………………….

15

2.2. Recommended Spacing between Sprimklers ………………………….

15

5.1. PE (Polyethylene) Pipes for Agriculture ……………………………...

42

5.2. LDPE Pipes Internal (Inner) Diameter and Wall Thickness ………….

43

5.3. HDPE Pipes Internal (Inner) Diameter and Wall Thickness …………. HDPE 5.4. PVC Pipes for Agriculture …………………………………………….

43

5.5. Internal Diameter and Wall Thickness of PVC Pipes …………………

44

7.1. Flow-rate of Spring Actuated Pressure Regulators ……………………

61

8.1. Relative Clogging Potential of Micro-emitters by Water Contaminants

72

8.2. Screen Perforation Examples ………………………………………….

74

8.3. Sand Particle Size and Mesh Equivalent ……………………………...

76

IX

44

8.4. Nominal Filter Capacity – examples …………………………………

78

9.1. Electric Charges of Nutrients …………………………………………

90

10.1. Pressure and Water Potential Units …………………………………...

91

10.2. Friction Coefficients …………………………………………………

93

10.3. Multiple Outlets factor F ………………………………………………

97

10.4. Effect of the Emitter Exponent on Pressure – Flow-rate Relationship .

97

10.5. Head Losses in Non-Distributing Aluminum Pipes, m. Head per 100m. Pipe Length (without Outlets) ……………………………………..

99

10.6. F Coefficient in Laterals ………………………………………………

100

11.1. Soil Classification According to Particle Diameter …………………...

109

11.2. Available Water in Different Soil Textures …………………………..

112

11.3. Average values of Water States in Different Soil Textures – W/W ….

112

11.4. Calculating Christiansen's Coefficient of Uniformity with Experimental Data (example) …………………………………………………………

127

12.1. Recommended Hose Size for Traveler Sprinklers ……………………

147

12.2. Characteristics and Performance of the Emitters ……………………..

165

12.3. Wetting Diameter of Emitters at 1.8 m3/h Flow-rate …………………

171

12.4. Recommended Spacing – m. for Emitters at 2 m. Height at Different Working Pressures …………………………………………………….

177

13.1. Sprinkler Performance (example) …………………………………….

199

13.2. Maximum Allowed Number of Sprinklers on Lateral on Level Ground

201

13.3. The Chosen Emitter …………………………………………………...

206

13.4. Allowed Length of Laterals …………………………………………...

206

13.5. Basic data ……………………………………………………………..

207

13.6. Head-loss Calculation …………………………………………………

208

13.7. Total Requested Dynamic Head ………………………………………

208

14.1. Annual Crops Irrigation Scheduling Form ……………………………

212

14.2. The Estimated Available Water per Unit of Rooting Depth for Soils of Various Textures and the Intake Rate for Various Soil Textures …….

214

14.3. Active Root-zone Depth of Fruit Trees ……………………………….

215

X

LIST OF FIGURES No.

PAGE

1.1. Level Border Strip Flooding …………………………………………

2

1.2. Leveled Beds between Contour Lines ………………………………..

3

1.3. Furrow Irrigation ……………………………………………………..

3

2.1. Sprinkler Spacing Positions ………………………………………….

5

2.2. Irrigation Intensity ……………………………………………………

5

2.3. The Influence of Wind on the Uniformity of Water Distribution ……

6

2.4. Outdated Pressurized Irrigation Systems ………………………..

6

2.5. Impact-Hammer Sprinkler ……………………………………………

8

2.6. Turbo-Hammer Sprinkler …………………………………………….

8

2.7. Gun Sprinkler (Rain-gun) …………………………………………….

8

2.8. Stand-alone Gun-sprinkler with Stabilizer in the Field ………………

9

2.9. Pop-up Sprinklers …………………………………………………….

10

2.10. Part-circle Static Sprinklers …………………………………………..

10

2.11. Impact Sprinkler Components ……………………………………

11

2.12. Configurations of Impact Sprinklers …………………………………

12

2.13. Nozzle Types …………………………………………………………

13

2.14. Jet Angles …………………………………………………………….

13

2.15. Low-volume Under-canopy Sprinklers ………………………………

14

3.1. Diverse Micro-emitters ……………………………………………..

16

3.2. Static Micro-jets ……………………………………………………...

17

3.3. Vortex Sprayer ……………………………………………………….

18

3.4. Vibrating Micro-jet …………………………………………………..

18

3.5. Modular Micro-emitter – Water Spreading Pattern ………………….

18

3.6. Rotating Micro-sprinklers ……………………………………………

19

3.7. Micro-sprinklers Configurations ……………………………………..

19

3.8. Modular Micro-sprinkler ……………………………………………..

19

XI

3.9. Mounting Alternatives of Micro-emitters …………………………...

21

3.10. Water Distribution by Micro-sprinkler at Different Flow-rates ……... (example) 3.11. Multiple-jet (Fan-jet) Emitter's Distribution Patterns ………………..

22

4.1. Schematic Plot Irrigation System …………………………………….

23

4.2. Electric Water Pumps ………………………………………………

23

4.3. Pump Type Classification ……………………………………………

25

4.4. Centrifugal Pump …………………………………………………….

27

4.5. Different Flow Patterns in Centrifugal Pumps ……………………….

28

4.6. Water Flow in Volute Pump …………………………………………

29

4.7. Deep-well Verical Turbine Pumps …………………………………...

30

4.8. Pump Impellers ………………………………………………………

31

4.9. Single-stage Pump ……………………………………………………

32

4.10. Multi-stage Pump …………………………………………………….

32

4.11. Solar Pumping System ……………………………………………….

33

4.12. A Variable-frequency Drive Controlls a Set of 3 Pumps …………...

33

4.13. Pump Efficiency Curve ………………………………………………

36

4.14. A Scheme of Pump Curves …………………………………………..

37

4.15. An Example of Pump Curves Plotted on One sheet ………………….

38

4.16. Horse-power Curves ………………………………………………….

38

4.17. Critical Points on the Pump Curve …………………………………...

39

6.1. Hermetic and Detached Band Couplers ……………………………..

46

6.2. Single Latch Couplers ……………………………………………….

46

6.3. Valve Adapters ……………………………………………………….

47

6.4. Adapter Made of Al-Pb Metal Alloy ………………………………...

47

6.5. Aluminum Lateral Assembly ………………………………………...

47

6.6. Plastic and Metal Connectors ………………………………………...

47

6.7. Lock Fastened PolyPropylene Connectors ……………………………….. 6.8. On-line Saddles ………………………………………………………

48

7.1. Water Supply Network .……………………………………………

49

XII

22

48

7.2. Typical Control Head ..……………………………………………..

49

7.3. Valve Types ………………………………………………………….

50

7.4. Manual Actuators …………………………………………………….

50

7.5. Globe Valve ………………………………………………………….

51

7.6. Angular Valve ………………………………………………………..

51

7.7. Single-seat Globe Valve ……………………………………………...

52

7.8. Double-seat Globe Valve …………………………………………….

52

7.9. Gate Valve ……………………………………………………………

53

7.10. Ball Valve Cutaway ………………………………………………….

53

7.11. Butterfly Valve ……………………………………………………….

54

7.12. Piston Valve ………………………………………………………….

54

7.13. Diaphragm Valve Components ………………………………………

55

7.14. Diaphragm Valves ……………………………………………………

55

7.15. Diaphragm Valve Working Pattern …………………………………..

55

7.16. Control Valve Actuators ………………………………….…………

56

7.17. Cutaway of Solenoid Valve …………………………….……………

56

7.18. Scheme of Solenoid Operation ………………………………………

57

7.19. Fail Closed (NC) Solenoid Valve – Components and Working Pattern ………………………………………………………………..

57

7.20. Hydraulic Control Valve ……………………………………………..

58

7.21. Check Valves …………………………………………………………

59

7.22. Pilot Controlled Hydraulic Pressure Relief Valves …………………..

59

7.23. Pilot Valves …………………………………………………………..

60

7.24. Pressure Regulators …………………………………………………..

60

7.25. Cross Section of Air-release Valves ………………………………

61

7.26. Atmospheric Vacuum Breakers ……………………………………...

62

7.27. Flow-meters ………………………………………………………….

63

7.28. Hydrometers – Cross-section ………………………………………...

64

7.29. Hydrometer – Manual and Remote-controlled Dial ………………...

64

XIII

7.30. Local Irrigation Controller ……………………………………..

67

7.31. SCADA Control System …………………………………………….

68

7.32. RTUs Connected to Field-unit (FU) by Cable ……………………….

69

7.33. Internet Mediated SCADA Network …………………………………

70

8.1. Screen Filter ………………………………………………………….

73

8.2. Screen Patterns ……………………………………………………….

74

8.3. Head Losses in Clean Screen Filters …………………………………

75

8.4. Disc Filter …………………………………………………………….

75

8.5. Media Filters …………………………………………………………

76

8.6. Sand Separator - Working Pattern ……………………………………

76

8.7. Hydro-cyclone Sand Separator – Head Losses and Optimal Flowrates …………………………………………………………………..

77

8.8. Manual Cleaning of Screen filters ……………………………………

79

8.9. Hose Flushing of a Disc-filter ………………………………………..

79

8.10. Continuous Flushed Circulating-filter ……………………………….

79

8.11. Automatic Screen Filters with Scanning Nozzles ……………………

80

8.12. Automatic Flushing of Disc-filter ……………………………………

80

8.13. High-capacity Media-filter Array …………………………………….

81

8.14. Back-flushing of Media-filters ……………………………………….

81

9.1. Fertilizer Tank ………………………………………………………..

84

9.2. Venturi Injector ………………………………………………………

85

9.3. By-pass Venturi Installation ………………………………………….

85

9.4. Piston and Diaphragm Hydraulic Pumps …………………………….

86

9.5. No-drain Hydraulic Pump ……………………………………………

86

9.6. Piston Pump Installation in Control Head ……………………………

87

9.7. Fertilizer Solution Flow-meter with Pulse Transmitter ……………………. 9.8. Mixer Array …………………………………………………………..

87

9.9. Electric Pump ………………………………………………………...

88

9.10. Tandem Back-flow Preventer ………………………………………...

89

XIV

87

10.1. Graphic Presentation of Friction Head ………………………………..

94

10.2. Feeding Micro-tube Connection ……………………………………...

95

10.3. Head-losses in Hydraulic Valves …………………………………….

95

10.4. Pressure Measurement ……………………………………………...

98

10.5. Slide-ruler for Head-loss Calculation in Pipes ……………………….

101

10.6. Nomogram for Hazen-Williams Formula …………………………..

103

10.7. Nomograms for Head-loss Determination In Polyethylene Pipes ……….

104

10.8. Nomogram for Local Hydraulic Gradient Determination in Accessories ……………………………………………………………

105

10.9. Nomogram for Calculation of Head-losses in LDPE Pipes ………….

106

10.10. Nomogram for Calculation of Head-losses in HDPE Pipes ………….

107

10.11. Nomogram for Calculation of Head-losses in PVC Pipes …………...

108

11.1. Visual Illustration of Soil Particle Diameter …………………………

109

11.2. Soil Texture Triangle ………………………………………………... ………………………………………………… 11.3. Illustration of the Water States in the Soil …………………………... ..11111111111111111111111 11.4. Water-air Ratio in Two Soil Types, 12 Hours After Irrigation ………

110

11.5. Illustration of the Available Water in the Soil ……………………….

112

11.6. Water Potential Values in the Different Water States in the Soil ……

113

11.7. Water Retention Curves in Different Soil Textures ………………….

114

11.8. The Sequence of Soil Moisture Determination by the Gravimetric (Oven Drying) Method ……………………………………………….

115

111 111

11.9. Edelman Dutch Auger ……………………………………………….. 11.10. Water Infiltration into the Soil – Curve ……………………………...

115

11.11. Soil Texture Triangle – Infiltration Rate Contours …………………..

116

11.12. Typical Infiltration Curves in Different Soil Textures ……………….

116

11.13. The Basin Infiltrometer ………………………………………………

117

11.14. Double Ring Infiltrometer ……………………………………………

118

11.15. The “Sprinkler Method” ……………………………………………...

119

11.16. Single Sprinkler Test …………………………………………………

122

XV

11.17. Single Lateral Test …………………………………………………...

123

11.18. Simultaneously Operated Laterals Test ………………………………

123

11.19. Open-air Test Plot and Covered Distribution Test Facility ………….

123

11.20. Grid of Catch Cans …………………………………………………...

124

11.21. Recording Form for Measurement of the Uniformity of Water Distribution …………………………………………………………..

125

11.22. Measured Water Amounts in One Quarter of the Wetted Area in Single-sprinkler Test ………………………………………………….

126

11.23. Single Sprinkler Distribution Pattern in Wind-less Conditions ……...

126

11.24. Wind Effect on the Distribution Pattern on Both Sides of a Single Lateral ………………………………………………………………...

128

11.25. Unilateral Presentation of the Distribution Pattern of a Mini-emitter ….

128

12.1. Hand-move Lateral …………………………………………………..

131

12.2. Hand-move Layout: 2” Aluminum Pipes, Spacing 6 X 12 m. 4 Laterals X 4 Positions………………………………………………… …………………………………………………………. 12.3. Coupling of Aluminum Pipe ………………………………………….

132

12.4. Ten-shift Manual Drag Under-canopy Sprinkler Array …………….

133

12.5. Orchard Under-canopy Micro-sprinkler Irrigation ……………… ……….………………. 12.6. Solid-set System in Orchard. Spacing 6 X 4 m. Sprinkler Flow-rate … 100 l/h 12.7. Orchard Overhead Irrigation …………………………………………

134

12.8. Solid-set Mini-sprinkler Irrigation of Vegetables ……………………

136

12.9. Towline ……………………………………………………………...

137

12.10. Towline Accessories ………………………………………………….

137

12.11. Linear Towline System: 2 Sets, 8 Laterals Each, Six Positions per Lateral, Spacing 12X18 m …………………………………………..

138

12.12. Sprinkler Vertically Stabilized by a Swivel and a Ballast …………...

139

12.13. Side-roll Operating Scheme ………………………………………….

140

12.14. Side-roll in the Field ………………………………………………….

140

12.15. Manually Moved Big Gun ……………………………………….

142

12.16. Hose-reel Traveler ……………………………………………………

143

XVI

132

134 135

12.17. Cable-tow Traveler …………………………………………………..

143

12.18. Hose-reel Traveler Operating Scheme …………………………..

144

12.19. Water-driven Cable-tow Traveler Scheme …………………………..

145

12.20. Cable-tow Traveler Operating Scheme ………………………………

145

12.21. Linear-Move System with On-top High-pressure Impact Sprinklers and End-gun ………………………………………………………….

148

12.22. Impact Sprinkler – Nozzle Options …………………………………..

148

12.23. Stationary Deflection-pad Emitters …………………………………..

150

12.24. Nozzle and Deflection-pad Options for Stationary Spray ……………

150

12.25. Micro-emitters On-drops in Work ……………………………………………….. 12.26. Nozzle and Pad Options in Rotators …..……………………………..

151

12.27. Up-right Spinner ……………..…….…………………………………

151

12.28. Rotators and Spinner …………………………………………………

152

12.29. Distinctive Emitters …………………………………………………..

152

12.30. LDN Emitters at Work ……………………………………………….

153

12.31. LDN (Low Drift Nozzle) Emitter Configurations ……………………

154

12.32. Oscillating Deflection Pad Options …………………………………..

155

12.33. Components of Oscillating Emitters …………………………………

155

12.34. Inverted Wobbler on Drops …………………………………………..

155

12.35. Diverse Configurations of Inverted Wobblers ………………………

156

12.36. Quad-spray and its Water Application Modes ………………………

156

12.37. Aerial View of Center-Pivot Irrigated Area ………………………….

157

12.38. Center-Pivot Operation Scheme ……………………………………...

157

151

12.39.

Net Irrigated Area ……………………………………………………

157

12.40.

Components of Center-Pivot / Linear-Move Lateral System ………..

158

12.41.

Universal System (Can Be Used as Linear-Move or Center-Pivot) ….

159

12.42.

Center-Pivot Main Tower ………………………………………….

160

12.43.

Corner Arm …………………………………………………………..

160

12.44.

Options of Sprinkler Position and Dicharge …………………………

161

XVII

12.45.

Towable Center-Pivot ………………………………………………..

163

12.46.

Goosenecks on Top of lateral ………………………………………...

166

12.47.

Positioning Options of Low-pressure Emitters on Drops ……………

167

12.48.

Furrow Dikes …………………………………………………………

168

12.49.

Boom-backs behind Center-Pivot Towers …………………………...

169

12.50.

Bi-lateral Boom Appendage with end-gun on a Center-Pivot ……….

170

12.51.

Emitter Spacing Patterns in Center-Pivot ………………………..

173

12.52. An Example of Water Logging by Spray Emitters - Close-up ………

174

12.53. The Effect of Using Pressure Regulators in Slopy Terrain ………….

174

12.54. Small-diameter Pressure Regulators Installed for Single Emitters ..… .and on Drops 12.55. Relationship between Width of the Wetted Coverage (W) and Application Intensity for the Same Flow-rate ………………………..

175

12.56. Relationship between Required Application Intensity and Time of Application for the Same Depth of Application ……………………..

177

12.57. Center-Pivot End-gun Installations …………………………………..

178

12.58. Irrigation of Orchards by Center-Pivot ………………………………. 12.59. Linear-Move Lateral …………………………………………………

179

12.60. On-lateral Trip Switch ……………………………………………….

183

12.61. Linear-Move System with Spray Emitters on Drops ………………...

184

12.62. Linear-Move System with Rotators on Drops ……………………….

185

12.63. Linear-Move – Main-line in Field Margin …………………...............

186

12.64. Linear-Move System Pumping Water from Ditch …………………...

186

12.65. Operation Scemes of Ditch-fed Linear-Move Systems ………………

186

12.66. VRI with Individual Emitter Control ………………………………...

188

12.67. VRI – Partially Irrigating Lateral …………………………………….

189

12.68. Individually Controlled Node ………………………………………..

189

12.69. Control Panel Positioned in the Pivot point ………………………….

189

12.70. On-screen Operation Presentation …………………………………...

191

13.1. Topographic Map …………………………………………………….

192

XVIII

176

182

13.2. Irrigation Planning Form ……………………………………………..

193

13.3. Different Design Alternatives ………………………………………..

202

13.4. Manifolds Save in Cost of Accessories ………………………………

202

13.5. Citrus Grove - 11.5 Ha. ………………………………………………

204

13.6. The Design Sceme ……………………………………………………

207

13.7. Hand-move Design Scheme ………………………………………….

209

13.8. Gun Traveler Design Scheme ………………………………………..

210

13.9. Solid-set in Orchard ………………………………………………….

211

14.1. Typical Root Systems of Field Crops ………………………………..

215

14.2. Irrigation Design Software Screenshot ……………….……………...

216

14.3. Visual Presention of Designed System ………………………………

217

14.4. Scheduling Software Screen-shot ……………………………………

217

14.5. On-line Calculator ……………………………………………………

218

15.1. Tensiometers …………………………………………………………

219

15.2. Watermark Granular Sensor ………………………………………….

219

15.3. Time Domain Transmissometry Sensor ……………………………...

219

15.4. The Pressure Bomb …………………………………………………..

220

15.5. Fertilizer and Water Controller ………………………………………

221

15.6. Integrated Monitoring and Control …………………………………..

222

16.1. Punch and Holder …………………………………………………….

223

16.2. Automatic Lateral End Flushing Valve ………………………………

225

16.3. Control Head …………………………………………………………

225

16.4. Coupling of PE Pipes ………………………………………………..

226

16.5. Replacing Seal ……………………………………………………….

226

16.6. Insertion of Emitters In Small-diameter Soft PE Lateral ….……….

227

16.7. Components of Hydraulic and Metering Valves. The Wearsensitive Components ………………………………………………

227

16.8. Sprinkler Tools ………………………………………………………

227

16.9. Sprinkler components ……………………………………………….

227

XIX

16.10. Micro-jets and Mini-sprinklers Components ………………………..

228

16.11. Vertical Stake ………………………………………………………...

229

16.12. Flow Regulator ………………………………………………………

229

XX

SPRINKLER IRRIGATION

1. INTRODUCTION 1.1 Overview Water scarcity, soaring energy costs, deterioration of agricultural land and desertification, threaten agricultural development and food production for the fast growing world population. Irrigated agriculture increases twice to ten-fold the yield per land unit, compared with non-irrigated farming. Irrigation has its roots in the history of mankind and is even mentioned in the Bible: “A stream flows from Eden to irrigate the garden...” (Genesis, 10). The prosperous ancient civilizations developed fresh water sources and delivery systems that were used for irrigation. In years of drought, people were forced to migrate in search of water. Unfortunately, innumerable wars were triggered by water scarcity. Rivers and streams are natural water conveyors. Natural and artificial lakes are used as water reservoirs. The construction of dams converts segments of rivers' courses into reservoirs and increases their water storage capacity. Following the introduction of pumps, pipelines were installed as water conduits. The pipes are made of steel, aluminum, concrete and plastic materials. Population growth triggered long distance conveyance of water and promoted the development of water engineering and the derived science of hydraulics. Irrigation can be regarded as the science of survival. Gigantic irrigation water supply projects were built throughout the ancient world. Among them: The 1,200 km long Grand Canal in China. Water supply and irrigation systems were constructed thousands of years ago in India and Sri Lanka. Today, engineers are still impressed by the sophistication of ancient water delivery systems and the irrigation techniques employed. The Romans constructed sophisticated aqueducts, dozens of km long to deliver water to the new built cities. In Egypt, food production is fully dependent on the Aswan dam that stores water for irrigation of the Nile valley and some of the adjoining desert and guarantees food supply to the population. Prior to the harnessing of electricity, water had to be conveyed by gravity, along natural slopes that required the construction of canal networks, for the water flow and excavating the water path accordingly. This practice had its limitation, since water could not be conveyed to the lands lying above the water sources. A remarkable revolution in irrigation technology commenced with the development of pumps that enabled lifting water above the height of the water source. Irrigation technologies are classified into two main categories: a. Surface (non-pressurized) irrigation - furrow, borders, flooding, basins, etc. b. Pressurized irrigation - sprinkler, spray and drip irrigation (including mechanized irrigation). Surface irrigation is regarded as the most wasteful irrigation technology. Irrigation efficiency is mostly below 40%. In sprinkler and mechanized irrigation, the efficiency ranges from 60% to 85%. In micro-irrigation, the efficiency can attain 90% - 95%. Salinization of irrigated lands is the most prevalent trigger of desertification (conversion of cultivated land to desert). More than one million hectares of arable land on the globe is lost annually due to salinization.

1

SPRINKLER IRRIGATION

Careful water application in optimal timing and dosage with timely salt leaching when needed, is a prerequisite for long-run sustainable agriculture and inhibition of salinization. Sprinkler irrigation, facilitates the elimination of salinization by leaching the accumulating salts out of the active root-zone by precise application of the required water amount. There are significant differences between surface and sprinkler irrigation in the pattern of water movement and distribution in the soil. Ponding of water on the soil surface, in furrows and small basins is common in surface irrigation while water ponding in sprinkler irrigation indicates the existence of non-permeable soil layers or exessive water application rate, above the percolation capacity of the soil. In today's raised standards of living, more attention is given to irrigation of residential and recreational facilities like home gardens, lawns, sports and golf courses. The equipment used is partially adapted from agricultural appliances and partially dedicated gear that is designed specifically for these facilities.

1.2. Surface Irrigation Surface irrigation is the most widespread irrigation technique used on the globe. More than 90% of the 280 million irrigated hectares in the world are irrigated by surface irrigation. Surface irrigation methods can be classified into a number of techniques. The selection of the method depends on factors such as cropping technology, climate, soil type, topography, water availability and distribution facilities, farmers mentality and tradition. The most significant soil factors are the structure and the physical properties of the soil: soil texture, soil permeability; water flow on the soil surface and its movement in the soil; field capacity and wilting point; soil aeration. The most relevant climate factors are precipitation and evaporation rates during the growing season. Thorough consideration of the above-mentioned factors and incorporation of advanced techniques as zero slope leveling, SCADA (Supervisory Control And Data Acquisition) and surge (intermittent, pulsating application of water flow) irrigation, may facilitate achieving, by this “ancient technology”, efficient water use, high yields and good produce quality.

1.2.1. Surface Irrigation Methods

Fig. 1.1. Level Border Strip Flooding 1.2.1.1. Level Border Strip Flooding The level border bed (broad-bed, or paddy) resembles a broad furrow (4 - 18 m wide), bordered by levees, with zero slope across its width and a longitudinal slope not greater than 1%. By opening the floodgate at the head of the bed, or by activating siphons, the bed is filled with water from a ditch or a furrow. This method, which is fit 2

SPRINKLER IRRIGATION

for appropriately leveled topographic structures only, requires some land leveling and a high water flow-rate. Wetting the bed during a short period of time prevents water losses beneath the root zone depth. The performance of the system should be examined by field tests (advance and retreat of water as a function of time). Rice, banana, alfalfa and other field crops are usually irrigated by this method. 1.2.1.2. Leveled Beds between Contour Lines This method is similar to border strip flooding, however the bed walls are contour lines as shown in the illustration to the right. 1.2.1.3. Furrows The water is distributed in the field by means of narrow ditches, each of them delivering water to one or two rows of plants. Obtaining good irrigation efficiency necessitates two stages of watering. In the first stage a high flow-rate is sent to wet promptly the soil surface along the entire furrow. Then a second lower flow-rate is delivered in a longer time period.

Fig. 1.2. Leveled Beds between Contour Lines

1.2.2. Advanced Technologies Zero slope leveling and surge irrigation are two procedures that increase irrigation efficiency in surface irrigation. These procedures can be applied with both flood and furrow irrigation. 1.2.2.1. Dead Level Layout When high precision land Fig. 1.3. Furrow Irrigation leveling, supported by laser sensors is applied, zero slope, dead level layout can be practical. Irrigation efficiency in this layout can be much higher than in the traditional layouts. Width of area between borders is limited to 100 – 150 m. 1.2.2.2 Surge Irrigation The principle of surge irrigation is the splitting of water application to several pulses. The first pulse is of high volume of water. It is aimed to wet as fast as possible the entire length of the irrigated bed or furrow without inducing erosion. That first flow partially seals the upper layer of the soil and enables the next pulses to be of smaller volumes for longer time periods, rendering even depth percolation along the flow path. Modern surge irrigation layouts employ automatic surge valves that direct water in alternating pulses to different sectors of the plot according to pre-planned timetable. 3

SPRINKLER IRRIGATION

2. SPRINKLER IRRIGATION 2.1. Introduction Sprinklers were first introduced at the beginning of the twentieth century as pressurized irrigation emitters for the irrigation of flower gardens. Later-on they were adapted to the irrigation of field crops, plantations and greenhouses. Sprinkler irrigation was extensively expanded after the Second World War when aluminum became a cheap and widely available commodity and flat land, suitable for non-pressurized irrigation became scarce. Sprinkler irrigation enables simultaneous operation of many laterals of sprinklers, facilitates accurate water measurement and regulation of the water application rate to the water intake rate of the soil.

2.2. Advantages a. Sprinkler irrigation is suitable to diverse topographic conditions like uneven lands and steep slopes that cannot be irrigated by surface irrigation. b. A vast selection of emitters and nozzles facilitates the matching of the water application rate to the intake rate of the soil. c. Uniform distribution of water in the field renders high water use efficiency. d. Easy and simple operation, only short training of the operators is required. e. Capability of accurate measurement of the applied water amount. f. Prospective high mobility of the irrigation equipment from one field to another. g. The operation of solid-set and mechaniized systems, minimizes labor requirement. h. Feasibility of frequent - small water dosage applications for germination, cooling, frost protection, etc. i. The closed water delivery system prevents contamination of the flowing water, decreasing the occurrence of emitter clogging. j. Convenient blending of fertilizers with the irrigation water. k. Handy integration with automation and computerized irrigation control devices.

2.3. Disadvantages and Limitations a. b. c. d. e. f. g. h. i. j.

High initial investment. Extra cost of the energy consumed for creation of water pressure. Sensitivity to wind conditions. Water losses by evaporation from soil surface, the atmosphere and plant canopy. Induction of leaf-diseases in overhead irrigation. Hazard of salt burns on wetted foliage in overhead irrigation. Washout of pesticides from the foliage in overhead irrigation. Interference of irrigation with diverse farm activities like tillage, spraying, harvesting, etc. Hazard of soil surface encrustation and enhancement of runoff from soil surface. Water losses in plot margins. 4

SPRINKLER IRRIGATION

2.4. Definitions 2.4.1. Pressure: a force acting on an area, expressed in units of kg/cm2, bars, atmospheres or PSI (Pounds per Square Inch).

2.4.2. Water head: the pressure at the base of a water column, expressed in meter units. The head in the bottom of a water column 10 m. high, is 10 m. = 1 bar. ≈ 1 atm.

2.4.3. Water amount: measured in volume units. In the metric system the common units are liter (l) and cubic meter (m3) (1,000 l = 1 m3).

2.4.4. Water flow-rate (discharge): the amount of water flowing through a certain cross-section per time unit. In the metric system the units are: m3/h or liter/h (l/h).

2.4.5. Wetting diameter: the diameter of a circle of soil surface, wetted by a certain sprinkler = twice the wetting radius of the sprinkler. Measured in meters. 2.4.6. Sprinkler spacing: the spacing between the sprinklers along and between the sprinkler laterals. For example: 12 m x 18 m.

a. Rectangular Position

b. Diagonal Position

Fig. 2.1. Sprinkler Spacing Positions

2.4.7. Irrigation Intensity: the force of the water drops exerted on the soil surface during precipitation. The intensity depends on the number of drops, their size, their velocity and the impact angle at which they hit the soil surface. The intensity is expressed in qualitative terms: high, medium, low.

a. High Intensity – Rough Droplets Fig. 2.2. Irrigation Intensity

b. Low Intensity – Fine Droplets

5

SPRINKLER IRRIGATION

2.4.8. Application (precipitation) rate: the amount of water applied to an area unit per a unit of time: 1 mm/h = 1 m3 per 0.1 Ha/h = 10 m3 per Ha per hour. 2.4.8. Irrigation interval: The time interval between two water applications = the period between the start of one irrigation cycle and the start of the following one. 2.4.9. Irrigation cycle: The period between the beginning and the termination of one irrigation event of a certain area. 2.4.10. Wind velocity: expressed in meters per second (m/sec.) or km/h units.

Fig. 2.3. The Influence of Wind on the Uniformity of Water Distribution

2.4.11. Nominal pipe diameter: The nominal diameter of steel and asbestoscement pipes, up to 10" is the internal diameter, measured in inches (1 inch = 25.4 mm.) In wider diameters, as well as in aluminum, plastic pipes and tubes the nominal diameter is the external diameter, measured in inches in aluminum pipes and in mm. in pipes made of plastic materials. 2.5. Sprinkler Types In the early years, water under pressure had been applied by nozzles mounted along oscillating galvanized cast iron pipes. The oscillating movement was driven by the inherent water pressure in the irrigation system. Another means for water distribution was perforated tin pipes laid on the soil surface.

a. Skinner Oscillating Pipe System

b. Perforated Pipe (Perf-O-Rain)

Fig. 2.4. Outdated Pressurized Irrigation Systems

After Benami & Ofen 1993

Contemporary sprinklers are made of metal and plastic materials. The sprinklers are mounted on metallic or plastic risers of various heights, corresponding to the irrigation technique and the crop canopy height. 6

SPRINKLER IRRIGATION

2.5.1. Sprinkler Classification Sprinklers are classified according to their function, pattern of operation, working pressure, flow-rate, materials from whom they are made, etc. 2.5.1.1. Sprinkler Function Sprinkler function classification is based on the crop and growing technologies, for whom the sprinkler type is designated. 2.5.1.1.1. General use: Impact sprinklers with jet angle of 300, one or two nozzles, are used for overhead irrigation in field crops, forage and vegetables, as well as in overhead irrigation in orchards, in hand move, solid-set and towed laterals. 2.5.1.1.2. Under-canopy sprinklers: used for irrigation in orchards. The jet angle is 40 70. This group is comprised of under-canopy impact-hammers, turbo-hammers, whirling sprinklers, mini-sprinklers, microsprinklers and microjets – rotors, spinners, sprayers and ray-jets (multiple jets). These emitters are used also for solid-set irrigation in vegetables and flowers in the open field and greenhouses and in mechanized irrigation. 2.5.1.1.3. Gun sprinklers: Used for irrigation of wide-scale field crops and forage areas, may be used as stand-alone units, in laterals, moved by hand or installed on self-propelled travelers and in center pivots and lateral move machines, as endguns. 2.5.1.1.4. Part circle sprinklers: These sprinklers are installed at lateral ends, plot margins and in specific situations in mechanized laterals in order to avoid water losses beyond plot borders and wetting of roads and sidewalks. 2.5.1.1.5. Regulated sprinklers: May be pressure-compensated or flow-regulated. Simplifies design and operation in harsh topography conditions. 2.5.1.1.6. Pop-up sprinklers: Used in irrigation of lawns, golf courses and residential areas. 2.5.1.1.7. Small-size impact and turbo-sprinklers: are used for under canopy irrigation in orchards, and overhead irrigation in open field and protected vegetables and flowers. 2.5.1.1.8. Static sprinklers are used in small residental gardens. 2.5.1.2. Pattern of Operation Sprinklers are operated by water pressure. A water jet that is ejected from a nozzle activates the moveable component of the sprinkler. 2.5.1.2.1. Rotating impact sprinkler: The water jet, emitted from the nozzle, hits the hammer arm, pushing it in counter-clockwise direction. A spring returns the arm back. Its strike on the sprinkler body results in rotary movement of the body in the opposite direction. The impact sprinklers are fitted with one, two or three nozzles. This sprinkler type is manufactured in diverse configurations. With a 300 ejection angle it is used for overhead irrigation of field crops and orchards. For under-canopy irrigation of orchards the recommended jet angles are 40-70. Initially. the sprinklers were made of metal, but later-on, plastic materials were also used. The wear of moving parts and nozzles made of reinforced plastic, is much lower than that of metallic ones. Although impact sprinklers are highly reliable, they require strict routine maintenance to guarantee consistent operation along time. 2.5.1.2.2. Turbo-hammer sprinkler: The water jet stirs a grooved wheel that hits the 7

SPRINKLER IRRIGATION

hammer. The impact of the hammer rotates the sprinkler. The turbo-hammer sprinklers are made of plastic material and are used for the irrigation of orchards, vegetables and gardens at low flow-rates.

Fig. 2.5. Impact-Hammer Sprinkler

Fig. 2.6. Turbo-Hammer Sprinkler From "Naan" Brochure

2.5.1.2.3. Gun Sprinklers

Fig. 2.7. Gun Sprinkler (Rain-gun) Big size hammer sprinklers are made of brass with two or three nozzles. The working pressure is high (4 - 8 bars). The sprinkler flow-rate range is 6 - 60 m3/h. Gun 8

SPRINKLER IRRIGATION

sprinklers are used for irrigation of forage and field crops in solid-set schemes, in Center-Pivot and Lateral-Move irrigation machines and as a traveling gun in "standalone" configuration.

Fig. 2.8. Stand-alone Gun-sprinkler with Stabilizer in the Field 2.5.1.2.4. Pop-up sprinklers - commonly used for lawn and golf courses irrigation. The sprinkler pops upwards at the beginning of the irrigation and falls back after shutdown into its underground housing, where it remains in stand-by position until the next irrigation. In the underground stand-by position it allows the undisturbed use of lawns, parks or golf courses, and does not interfere with lawn mowers' operation. There is a wide-range of pop-up sprinkler types, including part-circle sprinklers, as well as rise-ups of various heights. 2.5.1.2.5. Gear-driven sprinklers are used mostly in residential and public lawns irrigation. Some gun sprinklers are also driven by a turbine and velocity reduction gear. 2.5.1.2.6. Rotor and rotary stream sprinklers often incorporate a small water turbine which, by means of reducing gears, provides for slow, continuous nozzle or nozzle head rotation. Gear-drive mechanisms require clean water to prevent clogging and wear.

9

SPRINKLER IRRIGATION

a. Gear-driven b. Part-circle Impact Fig. 2.9. Pop-up Sprinklers

c. Pop-up Sprinkler Irrigating A Lawn

2.5.1.2.7. Static sprinklers – are made of brass or rigid plastic materials, without moving parts. These sprinklers are used mainly in residential gardens. They irrigate a full or partial circle. The wetting range is smaller as compared to rotating sprinklers. Manufacturers' catalogs provide the essential data about the a. Fixed Angle b. Adjustable Angle specifications and performance of the sprinklers. Information is Fig. 2.10. Part-circle Static Sprinklers given about flow-rate (Q), and the effective wetting diameter (D), in the range of the allowed working pressure (P). Additional data relate to the recommended spacing between sprinklers, the precipitation rate and distribution uniformity.

10

SPRINKLER IRRIGATION

2.5.2. Components of Impact Sprinklers 2.5.2.1. Base: It is the connection to the riser. It has internal or external thread, manufactured in diameters of 0.5” - 3". 2.5.2.2. Tube: It is inserted in the base and fixed to the body of the sprinkler. Between the base and the tube there are located 1 - 3 seals that function as bearings to smooth the rotation of the sprinkler and minimize wear from the friction of the tube with the base. 2.5.2.3. Sand protection mechanism: Consists of a thrust spring and an external plastic sleeve that prevents the intrusion of sand and grit from the outside. 2.5.2.4. Body: Accommodates the housings in which the nozzles are fitted and carries the moving parts of the sprinkler. The body can be of one of the configurations: 2.5.2.4.1 Bridge: In some sprinkler types, the hammer is connected to the body by means of a shaft fixed to a bridge between two vertical supports. The sprinkler rotation is activated by the impact of the hammer on one of the supports. The reverting spring surrounds the shaft.

Fig. 2.11. Impact Sprinkler Components

2.5.2.4.2. Crown: Other types of sprinklers are bridge-less. The spring is connected above the hammer by a plastic or metallic crown. Under frost or dusty conditions, an external plastic cover protects the spring. 2.5.2.5. Spring: Stimulates the rotation of the sprinkler by returning the hammer arm that was activated by the water jet that was emitted from the nozzle. In the Bridge Sprinkler, the spring is fixed within a fastening frame while in the Crown Sprinkler the spring is not fixed within the frame. In a Crown Sprinkler, the spring tension can be adjusted to the size of the nozzle and the water head. Springs are commonly made of copper, however when using reclaimed water, stainless steel springs are recommended. 2.5.2.6. Hammer arm: Activates the sprinkler rotation. Wetting range and distribution are determined by the number of strikes per minutes (30-60). There are two types of hammer arms: 2.5.2.6.1. Spoon drive: a rigid arm without moving parts, used in medium and high pressure conditions. 2.5.2.6.2. Wedge (dual action) drive: a plastic wedge is fitted on a shaft at the edge of 11

SPRINKLER IRRIGATION

the arm. Used in low-pressure conditions prone to malfunction for small diameter wetting. 2.5.2.7. Buffer: Absorbs partially the energy of the hammer impact to Minimize the wear of the body by the strikes and acts as a guide to the arm.

a. Spoon Drive

d. Bridge Sprinkler

b. Wedge (Dual Action) Drive

c. Part-circle Sprinkler

e. Crown Sprinkler

f. Protected Crown Sprinkler

Fig. 2.12. Configurations of Impact Sprinklers 2.5.2.8. Nozzles Each sprinkler is fitted with one, two or three nozzles. The nozzle type and size determine the flow-rate, the distribution pattern and uniformity and the droplets size. Nozzles are prone to wear and change of the flow-rate as well as the water distribution pattern. Irrigation water containing sand is abrasive and may expand the nozzle aperture and increase the flow-rate, as well as change the distribution pattern. Plastic nozzles are more resistant to abrasion than metallic ones. There are different types of nozzles. A circular cross-section of the nozzle's aperture, indicates a long range jet while an elliptic or half-crescent cross-section indicates a short-range wetting diameter. Maximum range is achieved by a jet angle of 300 related to the soil surface while in under-canopy sprinklers, 40 and 70 angles are dominant. Nozzle size is expressed as its diameter in mm. Since the nozzle crosssection is not always circular, size definition may be quoted as the nominal size that is equivalent to a nozzle of circular cross-section with an identical flow-rate. Ordinarily, the nozzle size is stamped on the nozzles. In plastic nozzles it is common 12

SPRINKLER IRRIGATION

to distinguish between different sizes by different colors.

Fig. 2.13. Nozzle Types

After S. Elhanani, 1961

The nozzle flow-rate (Q) depends on the water pressure head, the diameter of the nozzle's aperture and its friction coefficient. (Eq. 2.1) Where: Q = Nozzle flow-rate (discharge), expressed as liters per hour (l/h) P = Water pressure head, expressed in m (meters) D = Nozzle nominal diameter, expressed in mm C = Friction coefficient. Its value for small nozzles, up to 5.5 mm. = 0.95. For medium size nozzles, 5.5-8 mm. = 0.9 For large nozzles, over 8 mm. = 0.85. The pressure dependent flow-rate for a certain nozzle is: (Eq. 2.2) Where: Q1 = The flow-rate at the P1 head. Q2 = The flow-rate at the P2 head.

2.5.3. The Jet Angle The angle of the water stream ejected from the nozzle determines the range, the sensitivity to wind and the water distribution pattern. Larger angles, up to 450, render longer range but higher sensitivity to wind. For the irrigation of field crops a 300 angle is common, while for under-canopy irrigation in orchards, the prevalent angles are 40 - 70 .

Fig. 2.14. Jet Angles

13

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a. Impact Sprinklers Fig. 2.15. Low-volume Under-canopy Sprinklers

b. Turbo Sprinkler

2.5.4 Sprinkler Flow-rate Sprinklers are classified into three groups in respect to their flow-rate. 2.5.4.1. Low flow-rate: 20 - 500 l/h. Used in orchards, greenhouses and gardens. 2.5.4.2. Medium flow-rate: 500 - 5000 l/h. Used mainly for overhead irrigation in field crops, orchards, fodder and vegetables. 2.5.4.3. High flow-rate: Above 5 m3/h. Used in wide-spacing positioning and mechanized irrigating machines.

2.5.5. Working Pressure (Head) 2.5.5.1. Low pressure: Up to 2 bar (20 m.). Microjets, microsprinklers, minisprinklers, whirling sprinklers and turbo-hammer sprinklers. 2.5.5.2. Medium pressure: 2 - 5 bar (20 - 50 m.). Impact sprinklers. 2.5.5.3. High pressure: Above 5 bar (50 m.). Gun sprinklers and large impact sprinklers.

2.5.6. Sprinkler Spacing, Selection And Operation There are a number of elementary factors that have to be considered in the selection of sprinklers according to distinct operating conditions: a. The flow-rate and wetting diameter at different degrees of pressure. b. Crop spacing. c. The desired range of the pressure and the recommended spacing between emitters. d. Soil intake rate. The application rate has to be lower than the soil intake rate. e. Wind conditions during the irrigation season. f. Water quality. (Eq. 2.3) g. Wind velocities in the plot have to be considered in the selection of the sprinkler type as well as the spacing between the sprinklers. As the wind velocity is higher, the 14

SPRINKLER IRRIGATION

spacing will be smaller. Table 2.1. Wind Velocity Definitions: No wind Medium wind velocity Strong wind Very strong wind

0 - 1.0 m/sec. 1.0 - 2.5 m/sec. 2.5 - 4.0 m/sec. above 4.0 m/sec. Sprinkler overhead irrigation is not recommended.

Table 2.2. Recommended Spacing between Sprinklers Positioning Rectangular

Diagonal

Wind velocity m/sec

Spacing

No wind

60% of wetting diameter

2

50% of wetting diameter

3.5

40% of wetting diameter

More than 3.5

30% of wetting diameter

No wind

65% of wetting diameter

2

55% of wetting diameter

3.5

45% of wetting diameter

More than 3.5

30% of wetting diameter

The diagonal (staggered) position allows for wider spacing between sprinklers under windy conditions.

15

3. MICRO-EMITTERS 3.1. Introduction The term micro-irrigation relates to pressurized irrigation technologies employing water emitters with tiny apertures that deliver water at a low flowrate. The micro-emitters are classified into two principal groups: a. Emitters that distribute water through the air: micro-sprinklers, rotors, spinners, wortex emitters, vibrating emitters, microjets, sprayers, rayjets and foggers. There is no definite difference between sprinklers for irrigation and the microemitters that distribute water through the air in micro-irrigation. There is a controversy about the distinction between macro and micro emitters – the common division boundary is 60 – 120 l/h. b. Emitters that deliver the water directly to the soil – drippers and bubblers. These emitters are not covered in this booklet. The primary use of non-drip microirrigation technology is for the irrigation of Fig. 3.1. Diverse Micro-emitters orchards and greenhouses. Unlike sprinkler irrigation of field crops and vegetables, in which the desired result is rain-like uniform distribution over the entire irrigated area, in orchard irrigation, full cover and even distribution of water, is unattainable and is not necessary. The objective of orchard irrigation is to deliver a uniform amount of water to each tree and to distribute it in compliance with the distribution of the root system in the soil. There are still orchards that are irrigated by overhead sprinklers, particularly for frost and hot spell protection. In these orchards, the sprinklers employed are of the same types that are used for irrigation of field crops. Obviously, because of the interference of the canopy in orchards, an even distribution of water on the soil surface cannot be achieved. Overhead irrigation in orchards is favored when frost protection is a significant factor in the selection of the irrigation technology. However there are many drawbacks in the use of overhead sprinkler irrigation in orchards. It interferes with pest management by leaching the pesticides from the canopy and enhances leaf and fruit diseases. The energy consumption in overhead irrigation is higher than in undercanopy irrigation. The dominant technology in orchard pressurized irrigation, therefore, is under-canopy irrigation by low-volume, low-angle sprinklers, mini and micro-sprinklers, as well as microjets, sprayers and drippers. Recently, the use of micro-sprinklers had been extended to irrigation of vegetables and field crops. Micro-sprinklers are commonly built of rigid plastic materials. They are much smaller 16

and cheaper than conventional sprinklers.

3.2. Micro-emitter Types There are four emitter types: a. Static Micro-emitters b. Vortex Emitters c. Vibrating Micro-jets d. Micro-sprinklers

3.2.1. Static Micro-emitters (Micro-jets) Static micro-jets have no moving components and are classified into three groups: 3.2.1.1. Sprayers – the water stream is fragmented into tiny droplets by means of a static deflector. Water is distributed in a relatively short range and the tiny drops are wind-sensitive. In sprayers, the deflectors form a fine spray, providing uniform coverage that is essential in sandy soils. They are particularly useful for frost protection. However, they are susceptible to wind and bring about relatively high evaporation losses. The deflectors are produced in diverse styles that allow sector coverage from 450 to 3600. 3.2.1.2. Misters and Foggers – water droplets are smaller than in sprayers. Spread range is shorter. Wind sensitivity and evaporation losses are higher than in sprayers. This type is mostly used to increase the humidity in greenhouses and poultry coops, as well as for frost protection in orchards. 3.2.1.3. Multi-jet Emitters (Ray-jets, Fan-jets) – the water stream is splitted into 4 – 20 discrete jets. The wetting range is extended and wind sensitivity is reduced. Absence of moving parts increases its reliability compared with rotating microsprinklers.

a. Static Sprayer

b. Ray-jet

c. Mister

Fig. 3.2. Static Micro-jets

17

d. Fogger

3.2.1.4. Vortex Emitters These emitters have no moving parts. The water whirls in a circular vortex chamber that delivers a low flow-rate through a relatively large opening that reduces clogging hazard. The area wetted by this emitter is smaller than the wetted area by micro-sprinklers. 3.2.1.5. Vibrating Micro-jets Water ejected from a circular orifice strikes a deflector and triggers it to vibrate. The vibration of the deflector creates larger drops than those of sprayers, increases the distribution range and reduces evaporation and sensitivity to wind. The emitter is simple and reliable.

3.2.2. Micro-sprinklers

Fig. 3.3. Vortex Sprayer Fig. 3.4. Vibrating Micro-jet

Micro-sprinklers are manufactured in different configurations. Their distinctive characteristic is the rotation of the deflector or the nozzle around a central shaft. This facilitates wetting of larger area, compared with micro-sprayers. However, the inclusion of moving parts increases the susceptibility to the interference of external factors, as well as wear, tear and breakage of its components. During harvest operations, fruit pickers sometimes step on and break micro-sprinkler emitters and stakes. Herbicide spray booms and other tillage equipment can also damage the emitters. Most types of micro-sprinklers are modular. Many components are interchangeable and enable the modification of flow-rate, range, distribution pattern and droplet size, matching to specific requirements, at low cost.

Fig. 3.5. Modular Micro-emitter – Water Spreading Pattern Deflectors in diverse configurations allow sectorial coverage from 450 to 3600.

18

3.2.3. Micro-sprinkler Types 3.2.3.1. Rotors are manufactured in different configurations. The central shaft with the nozzle is static. The water jet hits a rotating deflector that distributes water in larger area than the vibrating emitters. 3.2.3.2. Spinners - the nozzle rotates and further increases the jet range, that is bigger than that of the rotators. The movement of components in micro-sprinklers increases their sensitivity to the interference of factors like weeds, precipitates and splashed soil particles. It also accelerates wear and tear. The damage danger from herbicide sprayer booms and other tillage equipment increases during harvest operations. Rotors' and spinners' configuration affects their sturdiness. There are two principal forms: unilateral and bilateral supports that hold the rotor/spinner swivel. Bi-lateral support provides improved holding to the rotating spinner or deflector, but the two vertical supports create dry sectors behind them.

a. Micro-sprinkler Components

a. rotor

b. spinner

Fig. 3.6. Rotating Micro-sprinklers

a. Unilateral Support

b. Bi-lateral Support

Fig. 3.7. Micro-sprinklers Configurations

b. Interchangeable Components

Fig. 3.8. Modular Micro-sprinkler 19

Pressure compensating and flow regulated micro-emitters are particularly suitable for irrigation of steep sloping plots. Micro-sprinkler systems require a higher volume of water supply compared with onsurface or buried drip systems. Dedicated micro-emitters had been developed for use on laterals in mechanized irrigation. They will be related in the chapter on mechanized irrigation.

3.3. Emitter Mounting Emitters can be mounted directly on the lateral, attached by a barbed or threaded protrusion. The most prevailing connection to the lateral is by means of a small diameter micro-tube. The vertical position of the emitter is secured by a stake, stabilizing rod or a weight (in upside-down positioning In greenhouses and mechanized irrigation). The emitter is raised 10 – 25 cm above soil surface to prevent water blockong and disturbance in the rotation of the moving parts of micro-sprinklers by weed interference and splashed soil particles. The micro-tubes are 50 – 100 cm long and 4 – 8 mm in diameter. To prevent excessive head losses, tube diameter of at least 6 - 8 mm is required for emitter flow-rates over 60 l/h and when the microtube length is over 60 cm. In greenhouses, micro-sprinklers, misters and foggers are frequently used to increase the relative humidity and lower the temperature of the ambient atmosphere. The misters and the foggers emit tiny droplets and are operated intermittently in pulses. These emitters are often mounted upside-down with the trajectory angle slanted downwards, in order to avoid hitting the glass or plastic ceiling. Threaded micro-emitters are installed on 1/2" – 3/4" rigid PVC risers. Barb microemitters can be mounted directly on the lateral. In greenhouses, micro-emitters may be installed upside down for overhead irrigation and misting. Weights are hung to stabilize them vertically. Micro-sprinklers are prone to clogging, but when clogging occurs it is quickly visually noticed and easily cleaned. Some emitters are equipped with a small integral valve to enable local water shut-down during the cleaning process. Some types of micro-sprinklers are prone to clogging by the eggs and excretions of spiders, ants and other insects. Insect-proof devices have been developed to prevent these obstructions. Spiders are capable of tying up spinners and halt their rotation. Micro-sprinkler operation can also be disturbed by sand that is splashed upward from the soil surface when hit by droplets from adjacent emitter. Blockage that is not removed on time in orchards that employ one emitter per tree may result in lower yields and reduced produce quality.

20

a. Sprayer on b. Upside-down Misters c. Micro-sprinkler on Rod Stake with Stabilizing Weights Fig. 3.9. Mounting Alternatives of Micro-emitters

d. Upside-down Micro-sprinkler

3.4. Water Distribution Patterns The emitter’s water distribution pattern is determined by its outlet (nozzle) and deflector geometry, trajectory angle, droplet size, pressure and flow-rate. The higher the trajectory angle (up to 300) and the larger the droplet size and flow-rate, the larger will be the wetting diameter in the range of the designed working pressure. The patterns of water distribution and wetting depth in the wetted area vary with the emitter type. In some emitters the wetting pattern is triangular. These emitters are suitable for overlapping and full wetting of the soil surface. In some emitters the deeper wetting depth is adjacent to the emitter while in others the water is distributed more evenly in most of the wetted area.

21

Fig. 3.10. Water Distribution by Micro-sprinkler at Different Flow-rates (example)

Fig. 3.11. Multiple-jet (Fan-jet) Emitter's Distribution Patterns From "Bowsmith" Brochure

3.5. Pressure Compensation Micro-sprinklers and micro-jets can be pressure compensating. That facilitates longer laterals and uniform application in harsh topographic conditions.

22

SPRINKLER IRRIGATION

4. THE IRRIGATION SYSTEM 4.1. Introduction The performance of a pressurized irrigation system depends on the available water sources, reservoirs and pumping facilities. The efficiency of energy use and water application is determines by the properties of the pumping unit and the water delivery and distribution network.

4.1.1. The Main Components of the Irrigation System a. b. c. d. e. f. g. h. i.

The pumping unit Supply pipeline Control head Mains and sub-mains Fig. 4.1. Schematic Plot Irrigation System Manifolds Layout After NDSU Extension Publication Laterals Risers Emitters Accessories: Valves, check-valves (backflow preventers), air release valves, vacuum valves, filters, couplers, risers, pressure and flow regulators, fertigation devices, etc.

4.1. The Pumping Unit While the water emitters are the core of the pressurized irrigation system, the pump is its priming element. The pump lifts water from the source (well, river, lake, reservoir, canal, etc.,), increases its energy and governs the capacity and the working pressure in the system. Pumps are activated by electric motors or internal conbustion engines and deliver water under pressure to the irrigation system. Water supply can be attained also from external water suppliers that are responsible for the appropriate pressure head in the connection point with the irrigation system. In some cases, the pressure in the supply connection point is too low and the farmer has to boost the water pressure by means of a booster pump. The energy use efficiency of electric motors is much higher than that of combustion engines. Hence, If electricity is available, it will be the preferred choice. If there is no electricity source, pumps can be operated by a diesel, kerosene or gas motor. The efficiency of the pumping unit is an important factor in water discharge, pressure head and energy costs. 23

Fig. 4.2. Electric Water Pumps

SPRINKLER IRRIGATION

The pumping unit is composed of three major components: The power unit, the transmission to the pump (drive or gear head) and the pump itself.

4.1.1. Pump Performance Terminology 4.1.1.1 Pump performance - Capacity is expressed as volume per time unit, e.g.: cubic meters per hour (m3/h) and the pressure as meters (m.) of head. In the imperial unit system it is designated as gallons per minute (gpm) and feets of head. In general, in a specific pump, a trade-off occurs between head and capacity. Increase in head brings about the decrease in capacity and vice versa. 4.1.1.2. Head refers to gains or losses in pressure due to change in topography and friction in the network. The following terms are used when referring to lift or head: 4.1.1.3. Static Suction Lift - The vertical distance from the water surface in the reservoir/well to the centerline of the pump's impeller. 4.1.1.4. Maximum suction lift - Pumps lift water with the support of atmospheric pressure. The practical suction lift, at sea level, is ~10 m. Later on, the pump imparts additional pressure to the water and discharges it from the casing. 4.1.1.5. Static Discharge Head — the vertical distance from the discharge outlet to the point of discharge or liquid level when discharging into the bottom of a tank. 4.1.1.6. Dynamic Suction Head — the static suction lifts plus the friction in the suction line. Also referred to as Total Suction Head. 4.1.1.7. Dynamic Discharge Head — the static discharge head plus the friction in the discharge line. Also referred to as Total Discharge Head. 4.1.1.8. Total Dynamic Head — the Dynamic Suction Head plus the Dynamic Discharge Head. Also referred to as Total Head. 4.1.1.9. Net Positive Suction Head (NPSH) – the head measured in the suction point. 4.1.1.10. Net Positive Suction Head required (NPSHr) - The minimum head requirement in the pump inlet. It takes into consideration head losses in the suction piping and connections, the elevation and absolute pressure of the fluid in the suction piping, the velocity of the fluid and the temperature, including what goes on in the eye of the pump's impeller. Some of these factors add energy to the fluid as it moves into the pump, and others subtract energy from the fluid. There must be sufficient energy in the fluid for the impeller to convert this energy into pressure and flow. If the energy is inadequate we say that the pump suffers inadequate NPSH. The NPSHr is actually the minimum suction pressure necessary to keep the pumped fluid in a liquid state and avoid cavitation in the pump. 4.1.1.11. Net Positive Suction Head available (NPSHa) The head available at the pump inlet. It has to exceed the NPSH required.

24

SPRINKLER IRRIGATION

4.1.2. Pump Types There is an extensive selection of pump types. Only a few of them are used in water pumping.

Fig. 4.3. Pump Type Classification According to the Hydraulic Institute (HI) Standards All pumps may be divided into two major categories, based on the pattern in which they transmit energy to the pumped fluid: a. Kinetic (dynamic) pumps b. Positive displacement pumps 1) In kinetic pumps, continuously added energy increases the velocity of the fluid. Later on, this velocity is converted into pressure. In centrifugal pumps, energy is imparted to the fluid by centrifugal action, by impeller or lifting action of a screw within a close-clearance bore. 2) In positive displacement pumps, intermittently added energy directly increases the pressure of the fluid. The reciprocating action of one or several pistons, or a squeezing action of diaphragms, meshing gears, lobes, or other moving elements, displaces the pumped fluid from the suction point to the discharge outlet. These pumps have limited capacities and are not suitable for pumping when large volume of water is required for irrigation or drainage. They are used mainly for injection of chemicals into irrigation systems and will be related in the chapter on fertigation. 4.1.2.1. Comparison of the Main Features between Kinetic and Positive Displacement Pumps 4.1.2.1.1. Flow-rate and Pressure Head The two types of pumps behave differently regarding pressure head and flow-rate:

25

SPRINKLER IRRIGATION

a. The Centrifugal Pump's flow varies, dependending on the system pressure (head). b. The Positive Displacement Pump's flow is constant, regardless of the system pressure (head). Generally, Positive Displacement Pumps are capable to generate higher pressure than Centrifugal Pumps. 4.1.2.1.2. Capacity and Viscosity Another significant difference between these two pump types is the effect of viscosity on the capacity: a. In Centrifugal Pumps the flow decreases when the viscosity is increased. Centrifugal Pumps are inefficient at even modest viscosity. b. In Positive Displacement Pumps the flow increases when viscosity is increased. Liquids with high viscosity fill the clearances of a Positive Displacement Pump causing a higher volumetric efficiency. The Positive Displacement Pump is better suited for high viscosity applications. That property is irrelevant to pumping of water, since water viscosity changes only slightly as a function of temperature change. 4.1.2.1.3. Mechanical Efficiency The pumps behave in different patterns considering mechanical efficiency. a. In Centrifugal Pumps changes in system pressure (head), affects significantly the flow-rate. b. In Positive Displacement Pumps changes in system pressure have little or no effect on the flow-rate. 4.1.2.1.4. Net Positive Suction Head - NPSH Another difference relates to the Net Positive Suction Head (NPSH). a. In a Centrifugal Pump, NPSH varies as a function of flow determined by pressure. b. In a Positive Displacement Pump, NPSH varies as a function of flow determined by speed. Reducing the speed of the Positive Displacement Pump reduces the NPSH. 4.1.2.1.5. Pump Velocity a. Since in centrifugal pumps the energy is imparted to the liquid by means of centrifugal force, the pressure generated is proportional to the square of the speed of the impeller. b. A positive displacement pump is simply pushing the liquid against whatever resistance that is put on its way. The speed at which it runs is irrelevant – the pressure it can generate is only a function of how mechanically strong the machine is.

4.1.3. Suction Lift of a Pump The theoretical suction lift or suction head is equal to atmospheric pressure divided by the density of the fluid being pumped. In case of plain water (cold) it is 10.33 meters or 33.9 feet. Hence for other fluids maximum suction lift is:

26

SPRINKLER IRRIGATION

(Eq. 4.1)

4.1.4. Kinetic Pumps Kinetic pumps are dynamic devices that impart the energy of motion (kinetic energy) to a liquid by use of a rotating impeller, propeller, or similar devices. Kinetic pumps are classified into two main groups: a. Centrifugal / Turbine pumps b. Special pump types: centrifugal screw, rotating case, viscous drag and vortex action. 4.1.4.1. Centrifugal Pumps The advantages of centrifugal pumps brought about that they became the pump of choice in water delivery. Compared with positive displacement pumps, the main benefits are smaller size and lower weight. Centrifugal pumps attain much larger flows in a compact device, without pressure and flow pulsations. They are much easier to control, unlike positive displacement pumps in which flow-rate can only be controlled by varying the speed, the flow-rate of a centrifugal pump can be adjusted simply by means of discharge throttling. Centrifugal pumps can be classified by impeller shape and characteristics. Impellers are grouped according to the major direction of flow with respect to the axis of rotation.

a. Cutaway

b. Pump Components

Fig. 4.4. Centrifugal Pump With respect to type of impeller, all centrifugal pumps can be classified into three groups: a. Radial-flow pumps b. Axial-flow pumps c. Mixed-flow pumps Centrifugal pumps can also be classified into four major groups depending on their design and application.

27

SPRINKLER IRRIGATION

a. b. c. d.

Volute pumps Turbine pumps Diffuser pumps Propeller pumps

Centrifugal pumps employ a rotating impeller to move water through a piping system. 4.5. Different Flow Patterns in Centrifugal Pumps The rotating impeller Fig. From Grundfos Pump Handbook increases water pressure by transformation of kinetic energy. As water is drawn into the pump, the rotating impeller releases kinetic energy into the water. When the water exits outward through the impeller vanes, the kinetic energy (velocity) is converted into pressure. Centrifugal pumps must be primed by filling them with water before they can be activated. Water has to flow into the pump when pressure at the center (eye) of the impeller is reduced below atmospheric pressure. Volute pumps and Turbine pumps are the two main centrifugal pump categories that control and maintain water pressure differently. 4.1.4.1.1 Volute Centrifugal Pumps The primary difference between volute pumps and turbine pumps is the presence or lack of diffusion vanes. In volute pumps there are no diffusion vanes, but the outer casing is a spiral. This shape reduces water velocity (and eventual pressure) by creating an equal flow of water as it moves around the spiral toward the discharge nozzle. The spiral is called a volute. Volute centrifugal pumps are used to pump from reservoirs, lakes, streams and shallow wells. They are also used as booster pumps in supply and irrigation pipelines. The impeller converts energy from the motor to the water by centrifugal force. The rotation of the impeller develops centrifugal forces that drive the water towards the impeller's external edge. The impeller is surrounded by a volute casing. The volute or stationary diffuser ring converts the kinetic energy into pressure energy and delivers the fluid to the pump discharge outlet. The horsepower input is proportional to the pumping water discharge and the pressure level. As the resistance of a system increases, the head will also increase. This in turn causes the flow-rate to decrease and will eventually reach zero. A zero flow-rate is only acceptable for a short period without causing to the pump to burn-out. Centrifugal pumps are designed for either horizontal or vertical operation. The horizontal configuration employs a vertical impeller connected to horizontal drive shaft. Horizontal centrifugal pumps are the most common in irrigation systems. They are relatively cheap, require less maintenance, easier to install and more accessible for inspection and maintenance than the vertical pumps. Since centrifugal pumps must be "primed" - completely filled with water, before they can operate, the suction line and the pump have to be filled with water and freed of air. Air tight joints and connections are particularly important on the suction pipe. Priming a pump can be done by hand operated secondary vacuum pumps, internal combustion engine or motor powered secondary vacuum pumps. 28

SPRINKLER IRRIGATION

Vertical centrifugal pumps may be mounted so that the impeller is immersed continuously in the water. In this case, priming is unnecessary. There are self-priming horizontal centrifugal pumps for special purpose use. Self priming is particularly essential where there are frequent electrical power outages. Self priming is requested also with the new generation of control panels for center pivots, where automatic restart is a programmable function. 4.1.4.1.2. Turbine Pumps In a turbine pump, multiple diffusion vanes surround the rotating impeller. As water is released from the center Fig. 4.6. Water Flow in Volute Pump (eye) of the impeller, it spins outwards as the impeller rotates. Around the impeller’s circumference are constructed diffusion vanes - passages that widen gradually and open into a circular or spiral casing. The main role of the diffusion vanes is to gradually reduce the velocity of water. The velocity is transformed into pressure. Once in the outer casing, the water circles around toward the outlet (nozzle), where it exits the pump. Heads over 300 m. are readily developed in a two-stage turbine pump. Vertical turbines have vertical drive shafts and are used to pump water from wells. The impeller has tight axial clearance and pump channel rings that decrease recirculation head losses. The channel rings create a circular channel around the impeller's blades from inlet to the outlet. The liquid entering the channel from the inlet is picked immediately by the vanes on both sides of the impeller and pushed through channel by the shearing action. The repeating process continuously increases water energy.

the up the the

4.1.4.1.2.1. Deep Well Turbine Pumps Deep well turbine pumps are used in cased wells or where the water surface is deeper than the practical limits of a volute centrifugal pump. Turbine pumps are also used with surface water systems. Since in this case, the water intake is continuously below the water surface, priming is not needed. Turbine pump efficiencies are comparable to or greater than most volute centrifugal pumps. They are usually more expensive than volute centrifugal pumps and more complicated to inspect and repair. There are two configurations: a. The pump is connected with a vertical gear shaft to a motor on top b. Submersible motor in water-proof case The turbine pump has three main parts: a. Head assembly b. Shaft and column assembly c. Pump bowl assembly

29

SPRINKLER IRRIGATION

The pump head is normally made of cast iron and designed to be installed on a foundation. It supports the column, shaft and bowl assemblies and provides a discharge outlet for the water. It supports an electric motor, a right angle gear drive or a belt drive. The shaft and column assembly provides a connection between the head and the pump bowls. The line shaft transfers the power from the motor to the impellers and the column that carries the water to the surface. The line shaft on a turbine pump may be either oil or water lubricated. Oil-lubricated pump has an enclosed shaft into which oil drips, lubricating the bearings. Water-lubricated pump has an open shaft. The bearings are lubricated by the pumped water. If the water contains fine sand, oil lubrication is a must. If the water is for domestic or livestock use, it must be free of oil and a water-lubricated pump have to be used. The impeller is enclosed by the pump bowl. Due to its limited diameter, each impeller develops a relatively low head. In most deep well turbine installations, several bowls are stacked in series one above another. This is called staging. A four-stage bowl assembly contains four impellers, all attached to a common shaft and creates four times the discharge head of a single-stage pump.

a. Motor on Top

b. Submersible

Fig. 4.7. Deep-well Verical Turbine Pumps

Impellers used in turbine pumps may be either semi-open or enclosed. The vanes on semi-open impellers are open on the bottom and they rotate with a close tolerance to the bottom of the pump bowl. The tolerance is critical and have to be adjusted when the pump is new. During the initial break-in period the line shaft couplings will tighten, therefore, after about 100 hours of operation, the impeller adjustments should be checked. After 30

SPRINKLER IRRIGATION

break-in, the tolerance must be checked and adjusted every three to five years or more often if sand is suspended in the pumped water.

4.1.5. Installation Turbine Pumps

of

Vertical

Deep well turbine pumps must have correct alignment between the pump and the power unit. Correct alignment is made easy by using a head assembly that matches the motor and column/pump assembly. The well has to be straight and perpendicular. The pump column assembly must be vertically Fig. 4.8. Pump Impellers aligned so that no component touches the well casing. If the pump column does touch the well casing, vibration will wear holes in the casing. A pump column out of vertical alignment may also cause excessive bearing wear. The head assembly must be mounted on a good foundation, at least 12" above the ground surface. A foundation of concrete provides a permanent and trouble-free installation.

4.1.6. Submersible Pumps Submersible pumps are particularly advantageous in pumping from exceptionally deep wells. In a conventional vertical wet-pit pump the motor is mounted on top at the surface, in the open air, driving the pump via a line shaft. The deeper the pump is, the longer the line shaft must be. Long shafts, particularly at high speed rotation, are susceptible to problems of misalignment and the intermediate bearings are prone to wear when there are any abrasive particles in the pumped liquid. Submerged motor drives the pump directly. Pumps can be submerged in depth of 2 km and more. Submersible pumps can be installed in caissons wider only slightly than the pump itself. The limiting factor with regard to the minimum diameter is usually the requirement for sufficient liquid circulation around the pump in order to keep the motor cool. A typical submersible pump is a turbine pump close-coupled to a submersible electric motor. Both pump and motor are suspended in the water, thereby eliminating the long drive shaft and bearing retainers required for a deep well turbine pump with motor on top. The pump is located above the motor, and the water enters the pump through a screen positioned between the pump and the motor. In submersible pumps, enclosed impellers are used because the shaft from the electric motor expands when it heats and pushes up on the impellers. The pump curve for a submersible pump is similar to that of a deep well turbine pump with motor on top. Submersible motors are smaller in diameter and much longer than ordinary motors. Because of their smaller diameter, their efficiency is lower than that of motors used with centrifugal or conventional deep well turbine pumps. Submersible motors are classified as dry or wet motors. Dry motors are hermetically sealed with high

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dielectric oil inside for lubrication, to exclude water from the motor. In wet motors the rotor and bearings are open to the well water and operate inside it. If water circulation through the motor is inadequate, it may overheat and burn out. Therefore, the length of riser pipe must be sufficient to keep the bowl assembly and motor completely submerged always and the well casing must be large enough to allow water to easily flow past the motor. Submersible pumps used for irrigation need three phase electrical power. Electrical wiring from the pump to the surface must be watertight with all connections sealed. Voltage at the motor leads must be within ±10% of the motor nameplate voltage. Because the pump is located inside the well, lightning protection should be wired into the control box. Submersible booster pumps can be mounted horizontally in a pipeline. Occasionally they are used as booster pumps in the suction lines of volute centrifugal pumps, where the water level fluctuates significantly along the season. Having a submersible pump in the suction line will convert the head at the inlet of the volute centrifugal pump from a suction head to a positive head.

4.1.7. Pump Stages The head generated by Volute and turbine pumps depends on the number of stages.

Fig. 4.9. Single-stage Pump

Fig. 4.10. Multi-stage Pump

4.1.7.1. Single-stage Pump a. It has one impeller keyed to the shaft. This is generally horizontal but can be vertical also. b. It is usually a low lift pump. 4.1.7.2. Multi-stage pump a. It has two or more impellers keyed to a single shaft and enclosed in the same casing. Pressure is built up in steps. b. The impellers are surrounded by guide vanes and the water is led through a by-pass channel from the outlet of one stage to the entrance of the next stage until it is finally discharged into a wide chamber from where it is pushed on to the delivery pipe. c. Multi-stage pumps are used essentially for high working head and the number of stages depends on the head required.

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4.1.8. Solar Water Pumps and Solar Water Pumping Systems DC powered pumps, are used in typical solar electric systems that have an inverter available. DC powered pumps are used for deep and shallow well pumping, stock tanks, irrigation and many other applications. DC pumps are different in many properties from the AC pumps that are ordinarily used in water delivery systems. DC pumps come in a variety of types: small pressure booster pumps, diaphragm and piston positive displacement pumps for wells, booster pumps, circulating pumps, groundwater sampling pumps etc.

Fig. 4.11. Solar Pumping System These low-power pumps allow building a solar pumping system for a deep well at a modest cost. They are cheaper than windmill operated pumps, and have peak output during dry, sunny weather when water is needed most. They can be installed and pulled by hand. They can pump from wells of very low yield that conventional pumps may suck dry in minutes. Pumps are available that pump as low as 120 l. per hour. Solar energy operated pumps require a dedicated controllers if they are to be powered directly by Photo Voltaic (PV) modules without battery backup.

4.1.9. Variable Speed Drives For years, the common means for decreasing excessive water pumping beyond the requested amount were throttling by valves or release of the excess water to reservoirs. These two techniques are energy wasteful and pose hazard of damage to the water system by excessive pressure. Nowadays, Variable Speed Drives (VSDs), known also as Variable Frequency Drives (VFDs), are extensively used in water pumping. They control the discharge by changing the velocity (rpm) of the impeller/turbine according to water demand and keep the pump operating at high energetic efficiency. It also protects the pump Fog. 4.12. A Variable-frequency Drive Controlls from mechanical damage by excessive a Set of 3 Pumps pressure and enhances its mechanical reliability. The old fashion valve throttling is expensive, contributes to higher energy and maintenance costs, and impairs control loop performance. Employing a throttled control valve, less than 50% open, on the pump discharge outlet, may accelerate component wear and slow valve response. Since Variable Frequency Drives allow pumps to run at slower speeds, the Mean Time Between Failures (MTBF) is extended.

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4.1.10. Selecting an Efficient Pumping Plant The efficiencies of individual pump types vary among types, manufacturers and models. The minimum acceptable pump efficiency is in the range 75-85%. Once the operating pressure (head) and system capacity (in m3/h) have been determined, pump characteristic curves should be consulted to select the most efficient pump for the specific requirements. 4.1.10.1. Power-unit Efficiency. Power-unit efficiency is important in pumping plant performance. As mentioned before, power sources are of two types: (a) internal combustion engines (either direct drive engines used solely for irrigation or tractors equipped with a power takeoff to drive pumps) and (b) electric motors. Power-unit efficiency is the efficiency with which chemical energy stored in the fuel (for internal combustion engines) or electrical energy (for electric motors) is converted to mechanical energy to drive the pump. Where electricity is available, it is the most efficient power source. The efficiency of electric motors ranges from about 80% for motors under 7.5 hp. to over 90% for motors of 75 hp. or more. Internal combustion engines are much less efficient. Diesel engine efficiencies range is 25-37% and kerosine engines are only 20-26% efficient. The difference in operating costs among various types of power units and pumps over the lifetime of the pumping plant, must be weighed against any savings in initial investment. η) 4.1.10.2. The Pump Efficiency (η The efficiency of a pump is determined by its hydraulic and mechanical performance. It is defined as the ratio of the useful power delivered by the pump (Water Kilowatts) to the power supplied to the pump shaft (brake horsepower). The efficiency of the pump is expressed as percentage or decimal fraction.

4.1.11. Maintaining Irrigation System Efficiency Well-designed irrigation systems with properly sized pumping plants will normally meet or exceed performance standards during initial use. However, over the lifetime of the system, mechanical components of the system wear, reducing the overall effficiency of the system. The common causes of low overall effficiency are discussed below. 4.1.11.1. Internal Combustion Engines. Each percentage decrease in engine efficiency increases fuel consumption by 3-5%. Pump engines should be tuned-up at the beginning of each irrigation season to ensure effficient performance. Air and fuel filters should be changed at manufacturers' recommended intervals. 4.1.11.2. Electric Motors. A buildup of dirt or oil, obstruction of cooling vents, worn or dragging motor bearings, and voltage surges caused by lightnings can cause electric motors to overheat. Overheating often leads to shorted wires in the winding and is the most common cause of low motor efficiency. Voltage surges can also cause damage to or misalignment of phases in three-phase motors, resulting in low motor efficiency. Misaligned shafts between motor and pump and over-tightened packing glands or seals can also reduce efficiency. Low efficiency caused by extended use (wear) can sometimes be corrected by replacing the accumulator brushes or having the motor rewound. In the case of small motors (20 - 25 hp. or less) it is usually more practical to replace the entire motor. Electric motors should be

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protected from rain and direct sunlight. 4.1.11.3. Matching System Components. Often, irrigation systems are altered from their original design, resulting in mismatching of components. Alterations such as adding or deleting sprinklers or laterals are often made without making corresponding adjustments to the pumping plant. A change in the depth of water in deep wells where the static head has declined, can alter the pumping conditions so that the pump no longer operates in the desired efficiency range. In some cases, the pump can be adjusted to resume operation within the recommended range. On turbine pumps the bowls can be adjusted and the impellers trimmed. If wear is excessive, bowls and impellers should be replaced. If an internal combustion engine is used, the system can sometimes be adjusted by changing the operating speed.

4.1.12. The Pumping Unit Efficiency The overall "wire-to-water" efficiency of a pumping plant is the relationship between the energy consumed (in kWh) and the amount of water or other fluid being delivered (m3/h) at a given pumping head (m.). The greater the overall efficiency of the pumping plant, the lower the overall pumping costs will be. The efficiency of the pumping unit depende on the efficiency of its 3 comonents: the power unit (electric motor or internal combustion engine), the pump and the transmission between them. The efficiency is the ratio of the output energy to the energy of input to the system. The output and the Input are expressed in terms of Water Kilowattes (WKW) of power being generated by the pump. WKW = Flow x TDH / 360

(Eq. 4.1)

Where: Flow is in m3/h TDH (Total Dynamic Head, another term for pressure) at the Best Efficiency Point (BEP) on the pump curve is expressed in m. of water head. Hence: WKW = m3/h Χ TDH/360 As mentioned before, the efficiency of electric motors is 75% - 95%. Internal combustion engines are much less efficient. Kerosine engines efficiencies is 20 – 26% and in diesel engines 25% - 37%. The efficiency of the transmission system (gears, shafts, pulleys, etc.) that transmit power to the pump can approach 95% – 97%. The efficiency of the pump itself is in the range of 75% - 85%. Efficiency under 70% commits checking and repairing the pump. Thus, the potential efficiency of an electric powered pumping plant if correctly designed, installed, and maintained is in the range of: (75% - 85%) x (95% - 97%) x (75% - 85%) = 60% - 70%

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Referring to the example in the curve at right, and putting in the numbers : M3 / HR X TDH / 360 = 68 x 76 / 360 = 14.36 WKW. The curve shows a 60% efficiency so: 14.36 water kilowatts / 0.60 efficiency = 23.93 Kilowatts required. If this number is lower than shown on the pump performance curve, the efficiency of the plump is questionable. As an example:

Fig. 4.13. Pump Efficiency Curve If the pump performance curve showed a requirement for a 30 Kilowatt input, the actual efficiency would be: 14.36 water horse power / 30 Kilowatts required = 48 % actual efficiency. A pump can operate over a wide range of flow and pressure combinations. That is, the same pump may be able to draw 250 m3/h at 20 m. head pressure or 125 m3/h at 30 m. head. However, each combination of flow and pressure (the combination is termed the “operating condition”) will result in a different pump efficiency. E.g., at 240 m3/h and 20 m. head, the pump may be operating at 80% efficiency. However, at 120 m3/h and 30 m. head it is operating at only 65% efficiency. These differences in efficiency are due to the physics of water flow through an individual pump, while a specific flow-rate may result in more or less turbulence than another. 4.1.12.1. Power Units The pump drive transmits power from the power generating unit to the pump. The line shaft of electric-driven pumps is connected directly to the motor shaft, eliminating the need for a pump drive. When the pump is driven by an internal combustion engine, the pump drive is a right-angle gear drive, that may change the RPM of the pump. The efficiency of a right-angle gear drive is about 95%. Belt drives may vary in efficiency from 85 to 95%. Calculation of the power requested on the pump shaft

N= QXH 270Xἠ

(Eq. 4.2)

Where: N = the requested power (HP)

Q = the pump discharge - m3/h. H = total required head (lift+friction losses+topographic losses+working pressure) m. (1 m. = 0.1 bar). η = the pump efficiency (decimal fraction). Conversion of the HP. Units to KW units as it is customary with electric motors is attainable by the ratio 1 HP = 0.7457 KW.

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4.1.13. Cavitation Cavitation can damage pumps, valves and other accessories. Pump cavitation is the formation of cavities on the back surface of an impeller, resulting in loss of contact between the impeller and the water being pumped (Walker, 1972). Cavitation occurs when the local static pressure is below the vapor pressure of the fluid. After the water enters a pump, its velocity increases, causing decrease in the head within the pumping unit. If the head falls too low, the water will vaporize, forming bubbles in the liquid. These bubbles collapse violently as they move to areas of higher pressure. The collapse of the bubbles occurs at sonic speed ejecting destructive micro jets of extremely high velocity, up to 1000 m/s, strong enough to cause severe wear of the pump components, particularly impellers. Pressure reduction occurs due to: a. inadequate submergence of the pump water intake; b. too high impeller speed that creates extremely low pressure behind the impeller; c. constrained pump intake route; d. high water temperatures which decrease the pressure needed to vaporize the water. As mentioned before, the pressure required to operate a pump satisfactorily and avoid cavitation is called Net Positive Suction Head (NPSH). The head available at the pump inlet has to exceed the NPSH required (NPSHr). The required NPSH is specified by the pump manufacturer. Cavitation is a common problem in pumps and control valves - causing serious wear, and damage. In pumps, Impeller surfaces and pump bowls will pit and wear. Cavitation reduces the life-time expectancy of the components. This may happen when the fluid accelerates in a control valve or around a pump impeller.

4.1.14. Pump Curves Pump manufacturers provide for each pump a set of curves from which The performance of the pump can be evaluated. In selecting a pump, one of the concerns is to optimize pumping efficiency. It is good practice to examine several performance charts at different velocities to learn if a specific model is more efficient than others. Whenever possible, the lowest pump speed should be selected, as this will decrease wear and tear of the rotating components. The available curves are: Performance, Efficiency, Horsepower¸ NPSH Requirement and System curve.

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Fig. 4.14. A Scheme of Pump Curves

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4.1.14.1. Performance Curve A performance curve is a plot of Total Head vs. flow-rate for a specific impeller diameter and speed. The plot starts at zero flow. The head at this point corresponds to the shut-off head of the pump. Starting at this point, the head decreases until it reaches its minimum. This point is sometimes called the run-out point and represents the maximum flow of the pump. Beyond this, the pump cannot operate. 4.1.14.2. Efficiency Curves The pump's efficiency varies throughout its operating range. This information is essential for calculating the motor power. The B.E.P. (Best Efficiency Point) is the point of highest efficiency of the pump. All points to the right or left of the B.E.P have a lower efficiency. The impeller is subject to axial and radial forces, which get greater the further away the operating point is from the B.E.P. These forces manifest themselves as vibration dependent on the speed and construction of the pump. The point where the forces and vibration levels are minimal is at the B.E.P.

Fig. 4.15. An Example of Pump Curves Plotted on One sheet 4.1.14.3. Horse-power Curves The horse-power curves are shown on the chart and give the power required to operate the pump within a certain range. For example (Fig. 4.16.), all points on the performance curve to the left of the 2 hp curve will be compatible with a 2 hp motor. All points to the left of 3 hp curve and to the right of the 2 hp curve will fit to a 3 hp motor. Fig. 4.16. Horse-power Curves The horsepower can be calculated from data of the Total Head, flow and efficiency at 38

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the operating point. 4.1.14.4. N.P.S.H. Requirement Curves The pump manufacturer specifies the minimum NPSH required (NPSHr). in order for the pump to operate at its designed capacity. The NPSHr becomes higher as flow increases, and lower as flow decreases. The meaning is that more pressure head is required at the pump suction for high flow than for low flow. Since NPSH is a head term, it is independent of the fluid density and is expressed as absolute fluid column height. 4.1.14.5. System Curve The system curve is a plot of the Total Head vs. the flow for a given system. The higher the flow, the greater the head required. The shape of the system curve depends on the type of system being considered. The system curve is superimposed on the pump performance chart. The Total Static head is constant and the friction head, equipment head and velocity head are flow dependent. The calculation of Total Head at different flow-rates produces a plot of Total Head vs. flow that is called the system curve.

Fig. 4.17. Critical Points on the Pump Curve

The operating point is the point on the system curve corresponding to the flow and head required. It is also the point where the system curve intersects the performance curve. The design system curve is usually calculated with some extra flow capacity

4.1.15. Pump and Well Testing Pump testing is an important testing procedure. It is typically done when the pump is disconnected from the irrigation system. A flow-meter, pressure indicator and valve are installed on the pump exit. The pump is started and the valve is gradually partially closed, until the design system pressure is attained. The system is allowed to run for a period of 15 minutes, and then the valve is fully opened and closed again in order to obtain enough points to draw a pressure / flow curve. The static water level should be recorded at each flow point. The net positive suction pressure of the pump should be determined to ensure that the pump is immersed deep enough in the well to prevent cavitation. It is recommended that pumps and wells will be tested every 2 years when are operated full-season.

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5. PIPES AND ACCESSORIES 5.1. Introduction In pressurized water supply and irrigation systems, Water delivery and distribution is done by means of pipes and tubes. Actually, a pipe is a hollow cylinder in a specified length. Most pipes have circular cross-section. Pipes may be also of rectangular cross-section, but those pipes are used in construction and not for water delivery. Apart from water delivery, pipes are used for conveying different fluids – oil, gas, slurry, industrial liquid compounds and in some circumstances also powders. The terms pipe and tube are commonly used interchangeably. In most of the world the common term is pipe. In the USA, there is a distinction between pipes that are manufactured to international or national standards and are specified by outer nominal diameter and schedule that indicate the wall thickness. Tubes are made to custom sizes, in a broader range of diameters and tolerances and are specified by outer diameter (OD), inside diameter (ID) and the exerted wall thickness. In pipes the schedule indicates the wall thickness that determines the allowed working pressure. In tubes, the working pressure is defined more explicitly by the class definition of the allowed working pressure in bars or kilopascals (KPa). Pipes are made of a variety of materials: Metals: cast iron, ductile cast iron, carbon steel, galvanized steel, wrought steel, stainless steel, aluminum and copper. Concrete, ceramic and compound materials: reinforced concrete, ceramic, asbestos cement. Plastic: PolyVinyl Chloride (PVC), UPVC (Unplasticised PVC), CPVC (Chlorinated PVC), PolyEthylene (PE), PolyPropylene (PP), Glass Reinforced Polyester (GRP).

5.2. Pipe materials 5.2.1. Iron, Steel and Copper Cast iron was in extensive use in the early years of pressurized irrigation. Due to its vulnerability to corrosion, its life expectancy time-length was relatively short. Pitting and rust accumulation on the inner wall surface decreased the wall smoothness and increased friction head losses in the flowing liquid. Ductile cast iron had improved pipe performance but corrosion remained a severe disturbance. Carbon steel further improved pipe functioning. Later on, in order to avoid corrosion, the inner wall surface was coated by reinforced cement that kept wall smoothness and prevented corrosion. Steel pipes are expensive and are used mainly in water supply networks. In underground installed pipes, the outer wall surface is coated with asphalt, to avoid damage to the outer surface by corrosive elements in the soil. Stainless steel is too expensive to be used in irrigation and water supply networks. Copper is used mainly in residential and industrial plumbing. In irrigation systems, copper small diameter tubes are utilized in hydraulic control devices of automated systems. Galvanized tin pipes were used in the past in hand-move irrigation but were replaced by aluminum pipes.

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5.2.2. Aluminum The use of aluminum pipes for irrigation commenced after WWII. They replaced the galvanized tin pipes used in hand-move irrigation. Their low weight and sturdiness eased the operation of hand-move systems. High quality pipes were manufactured from corrosion resistant aluminum known as alclad aluminum. Aluminum pipes are manufactured in two technologies. In one of them, pipes are produced from aluminum flat sheets that are rounded and welded. The other technology is extrusion, in which seamless pipes are produced.

5.2.3. Asbestos-cement Pipes made of asbestos-cement were in wide-scale use in water supply networks and as mains for irrigation. The use of these pipes is now prohibited because it was found that asbestos fibers are carcinogenic, endanger workers in the production line and may disintegrate by some chemicals inherent in the water and endanger the users.

5.2.4. Concrete Concrete pipes are used mainly in drainage and sewage systems.

5.2.5. Plastic Materials 5.2.5.1. Overview After the introduction of aluminum pipes that were used mainly in hand-move irrigation, began the production of pipes made from plastic materials for use as replacement of galvanized iron pipes as laterals and single emitter extensions as well as replacement to carbon-steel pipes in water supply networks and as distributing mains, sub-mains and manifolds in the irrigated parcels. Plastics are solid materials comprised of one or more polymeric substances that can be shaped by molding or extrusion. Polymers, the basic ingredient of plastic materials, are a broad class of materials that include natural and synthetic substances. In professional terminology, polymers are frequently defined as resins. For example, a PolyEthylene (PE) pipe compound consists of PE resin combined with colorants, stabilizers, anti-oxidants and other ingredients required to protect and enhance the quality of the material during the fabrication process and the operation in the field. Plastic materials are divided into two basic groups: thermoplastics and thermosets, both of which are used for the production of plastic pipes. Thermoplastics include PolyEthylene (PE), PolyPropylene (PP), PolyButylene and PolyVynil Cloride (PVC). These materials can be re-melted by heat. The solid state of thermoplastic materials is the result of physical forces that immobilize polymer chains and inhibit them from slipping past each other. When heat is applied, these forces weaken and allow the material to soften or melt. Upon cooling, the molecular chains stop slipping and are held firmly against each other in the solid state. Thermoplastics can be shaped during the molten phase of the resin and therefore can be extruded or molded into a variety of shapes, such as pipes, flanges, valves, sprinklers and microsprinklers components, drippers and other accessories. Thermoset plastic materials are similar to thermoplastics prior to a chemical reaction (“curing”) by which the polymer chains are chemically bonded to each other by new

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cross-links. That is usually performed during or right after shaping of the final product. Cross-linking is the random bonding of molecules to each other to form a giant threedimensional association. Thermoset resins form a permanent insoluble and infusible shape after applying heat or a curing agent. They cannot be re-melted after shaping and curing. This is the main difference between thermosets and thermoplastics. As heat is applied to a thermoset component, degradation occurs at a temperature lower than the melting point. Thermosetting resins can be combined with reinforcements to form strong composites. Fiberglass is the most popular reinforcement and fiberglassreinforced pipes (FRP and GRP) are a common form of thermoset-type pipes. 5.2.5.2. Polyethylene Polyethylene (PE) is the most prevalent material in pipes and laterals in pressurized irrigation systems. There are four types of PE, classified by material density: Type I – Low Density (LDPE), 910 – 925 g/l Type II – Medium Density (MDPE), 920 – 940 g/l Type III – High Density (HDPE), 941 – 959 g/l Type IIII – High Homo-polymer, 960 and above g/l Two percent, by weight, of carbon black agent are added to increase pipes’ resistance to the detrimental impact of exposure to ultraviolet (UV) sun radiation. Another classification relates to the working pressure that the pipe withstands (PN). Common grades of PN used in irrigation are: 2.5, 4, 6, 10, 12.5 and 16 bars (atm). Certain thin-walled laterals withstand lower PN: 0.5 – 2 bar. The pressure tolerance depends on pipe material density and wall thickness. Tolerance data published by the manufacturers relate to standard temperature of 20 C0. At higher temperatures, the tolerance decreases significantly, hence pipes are tested at twice the designated working pressure. Plastic pipes are designated according to their external diameter, in mm. In the USA and some other countries, pipe diameter is marked in imperial inch units (“). 1” = 25.4 mm. Pipe wall thickness is designated in mm units (in the USA by mil units. Mil = 1/1000 of inch). 1 mil = 0.0254 mm. Laterals are commonly made of LDPE (PE – 32 grade) while delivering and distributing pipes of diameters greater than 32 mm are mostly made of HDPE. HDPE pipes are further classified according the grade of the material: PE-63, PE-80, PE-100. The higher the grade, the higher the pipe quality and pressure tolerance. Table 5.1. PE (PolyEthylene) Pipes for Agriculture PE type LDPE LDPE LDPE LDPE LDPE HDPE HDPE HDPE

ND (Nominal Diameter) 6 mm 4 – 10 mm 12 – 25 mm 12 – 25 mm 16 – 32 mm 32 – 75 mm 40 – 140 mm 75 – 450 mm

Applications Hydraulic command tubing Micro-emitter connection to laterals Thin-wall drip laterals Thick-wall drip laterals Micro and mini emitter laterals Sprinkler laterals Main lines and submains Water supply and delivery networks

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PN - m 40 – 120 40 – 60 5 – 20 25 – 40 40 – 60 40 – 60 40 – 100 60 - 160

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Table 5.2. LDPE Pipes Internal (Inner) Diameter and Wall Thickness - mm PN OD ↓

25 m

40 m

60 m

80 m

100 m

mm

ID

Wall thickness

ID

Wall thickness

ID

Wall thickness

ID

Wall thickness

ID

Wall thickness

12 16 20 25 32 40 50

9.8 13.2 17.0 21.8 28.8 36.2 45.2

1.1 1.4 1.5 1.6 1.6 1.9 2.4

9.6 12.8 16.6 21.2 27.2 34.0 42.6

1.2 1.6 1.7 1.9 2.4 3.0 3.7

9.2 12.4 15.4 19.4 24.8 31.0 38.8

1.4 1.8 2.3 2.8 3.6 4.5 5.6

8.6 11.6 14.4 18.0 23.2 29.0 36.2

1.7 2.2 2.8 3.5 4.4 5.5 6.9

8.0 10.6 13.2 16.6 21.2 26.6 33.4

2.0 2.7 3.4 4.2 5.4 6.7 8.3

Adapted form Plastro brochure

ND = Nominal Diameter OD = External (Outer) Diameter. In plastic pipes, mostly equivalent to the ND. ID = Internal (inner) Diameter

Table 5.3. HDPE Pipes Internal (Inner) Diameter and Wall Thickness - mm PN

25 m

40 m

60 m

80 m

100 m

160 m

OD

mm ID 12 16 20 25 32 40 50 63 75 90 110 125 140 160 180

46.8 59.8 71.2 85.6 104.6 118.8 133.0 152.0 172.2

Wall thickness

1.6 1.6 1.9 2.2 2.7 3.1 3.5 4.0 4.4

ID

28.8 36.8 46.0 58.2 69.2 83.0 101.6 115.4 129.2 147.6 166.2

Wall thickness

1.6 1.6 2.0 2.4 2.9 3.5 4.2 4.8 5.4 6.2 6.9

ID

21.8 28.2 35.2 44.0 55.4 66.0 79.2 96.8 110.2 123.4 141.0 158.6

Wall thickness

1.6 1.9 2.4 3.0 3.7 4.7 5.5 6.6 8.1 9.2 10.3 11.8

ID

16.8 21.1 27.2 34.0 42.6 53.6 64.0 76.8 93.8 106.6 119.4 136.4 153.4

Wall thickness

1.6 1.9 2.4 3.0 3.7 4.7 5.5 6.6 8.1 9.2 10.3 11.8 13.3

ID 12.8 16.2 20.4 26.2 32.6 40.8 51.4 61.4 73.6 90.0 102.2 114.6 130.8 147.2

Wall thickness

1.6 1.9 2.3 2.9 3.7 4.6 5.8 6.8 8.2 10.0 11.4 12.7 14.6 16.4

ID 8.6 11.6 15.4 18.0 23.2 29.0 36.2 45.8 54.4 65.4 79.8 90.8 101.6

Wall thickness

1.7 2.2 2.8 3.5 4.4 5.5 6.9 8.6 10.3 12.3 15.1 17.1 19.2

Adapted form "Plastro" brochure

5.2.5.3. PVC Pipes PVC (PolyVinyl Chloride) is a rigid polymer. Addition of plasticizers renders flexibility to tubes made of soft PVC. PVC pipes are sensitive to UV sun radiation. Soft and flexible, they are used mainly in gardening and landscape. In agriculture and water supply systems, rigid PVC pipes are mainly used for water delivery and distribution. PVC pipes are installed only underground to avoid damage from UV radiation. Currently, un-plasticized PVC (UPVC) pipes are manufactured with improved UV and pressure surges tolerance. PVC pipes appear in discrete 4 – 8 m long segments and have to be attached in the field. The working pressure of rigid PVC pipes is 6 – 24 bars (60 – 240 m).

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Table 5.4. PVC Pipes for Agriculture ND

PVC type Soft PVC

6 mm

Soft PVC

Applications

PN - m

Hydraulic command tubing

40 – 80

6 – 10 mm

Micro-emitter connection to laterals

40 – 60

Soft PVC

12 – 25 mm

Tapes and thin-wall drip laterals

5 – 20

Rigid UPVC

½” – 4”

Rigid UPVC

63 – 1000 mm

Risers

40 – 100

Supply networks, main lines, submains

40 – 240

When PVC pipes are installed in heavy or stony soil, it is recommended to pad the trench with sand to prevent damage to the pipe wall by swelling soil pressure and contact with sharp protrusions of stones. Table 5.5. Internal Diameter and Wall Thickness of PVC Pipes 60 m

PN------>

80 m

100 m

OD - mm

ID - mm

Wall thickness mm

ID - mm

Wall thickness mm

ID - mm

Wall thickness mm

63 75 90 110 140 160 225 280 315 355 400 450 500

59.0 70.4 84.4 103.2 131.4 150.2 210.2 262.8 295.6 333.2 375.4 422.4 469.4

2.0 2.3 2.8 3.4 4.3 4.9 6.9 8.6 9.7 10.9 12.3 13.8 15.3

58.2 69.2 83.0 101.6 129.2 147.6 207.8 258.6 290.8 327.8 369.4 415.6 461.8

2.4 2.9 3.5 4.2 5.4 6.2 8.6 10.7 12.1 13.6 15.3 17.2 19.1

57.0 67.8 81.4 99.4 126.6 144.6 203.4 253.2 285.0 321.2 361.8 407.0 452.2

3.0 3.6 4.3 5.3 6.7 7.7 10.8 13.4 15.0 16.9 19.1 21.5 23.9

5.2.5.3.1. Lay-flat Hoses Flexible PVC lay-flat hoses can be used as mainlines and sub-mains as well as feeding pipes in mechanized irrigation systems. The hose is impregnated with antiUV radiation protecting agents. When the water is shut-off, the hose lays flat on the ground and can be crossed-over by tractors and other farm machinery. The lay-flat hoses can be laid out on the soil surface or in a shallow trench. These hoses are available in diameters of 75 – 200 mm. 5.2.5.4. Fiberglass Pipes In addition to UPVC and HDPE pipes, reinforced fiberglass pipes are used to deliver water under high pressure from the water source to the irrigated area, as a substitution for steel and asbestos-cement pipes. GRP (Glass Reinforced Polyester) fiberglass pipes are manufactured in diameters of 300 – 3600 mm and PN grades of 40 – 250 m. They are particularly useful in delivery of reclaimed water.

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5.3. External and Internal Pipe Diameter The internal diameter (ID) of a pipe can be calculated by deducting twice the wall thickness from the external diameter (OD). In most cases, the designated nominal pipe diameter (ND) is its external diameter. Friction head losses of water flow in the pipe are determined by the internal diameter. It is imperative to check whether the designated diameter is nominal (mostly external) or internal, when using nomograms, on-line calculators and design software.

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6. COUPLERS 6.1. Connectors (Fittings) Connectors are made of metal or plastic materials. They may be two-sided straightthrough or angular units, T or Y shaped triple outlets, four-sided crosses or multioutlet splitters.

6.1.1. Aluminum Couplers Aluminum couplers are used for connecting two pipes. In some couplers there are outlets for sprinkler risers.

a. Hermetic Couplers

b. Detached Band Coupler

c. Elbow

Fig. 6.1. Hermetic and Detached Band Couplers Hermetic couplers are used to connect pipes in main supply lines and sub-mains that will be laid in the field at least for one whole season. Dual band couplers are widely used. They are manufactured in diameters of 1.5, 2, 3, 4, 5 and 6".The coupler is attached to the pipe by means of two clamps and two rings. There are rubber seals at both the inlet and the outlet of the coupler to prevent leakage during irrigation and to facilitate drainage after water shut-off. There are distinct seals for high and for low pressure. The couplers are reliable, easily detached from the pipe for transportation on trailers, symmetrical in construction and easy to assemble. In towlines the couplers are affixed to the wheels or to slide supports. Drainage of the pipe after water shutoff can be accomplished through a drain valve that is mounted in the middle of the pipe

Fig. 6.2. Single Latch Couplers Single latch couplers are manufactured in 1, 1.5, 2, 3, and 4" diameters. They are permanently fixed by screws at the end of the pipe. They are used mainly in handmove and tow systems, due to their convenient dismantling.

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In each style of couplers there are different models such as starter elbows for connecting the lateral to the hydrant; elbows; reducing adapters for changing diameters, end plugs, etc. Adapters made of Al-Pb metal alloy should be installed as an isolating interface between Fig. 6.3. Valve Adapters aluminum couplers to components made of other metals to prevent the fusion of the metal with the aluminum.

Fig. 6.4. Adapter Made of Al-Pb Metal Alloy

For hand-move laterals in high-canopy crops, like maize, there are quick couplers that facilitate fast disconnecting of the riser from the lateral. Risers are made of galvanized iron, aluminum or P.V.C. One or both edges are threaded. The common risers for sprinklers are of ½", ¾” and 1” diameter.

Fig. 6.5. Aluminum Lateral Assembly

6 . 1 . 2 . Po l y p r o p y l e n e Co u p l e r s

Fig, 6.6. Plastic and Metal Connectors Their functions are identical to those of aluminum couplers. They are manufactured in diverse sizes and shapes.

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There are two main groups: external and internal couplers. In the external type, the pipe is inserted into the coupler and is held by one or more grooved rings. The internal type is inserted inside between two pipe segments. There is also a combination of the two methods - external and internal fasteners in one unit. The external type is the most prevalent form used in sprinkler irrigation. These couplers are cheap, manufactured from rigid plastic materials such as polypropylene, which provide strength and endurance.

Fig. 6.7. Lock Fastened Polypropylene Connectors

Sprinklers are attached to the laterals in three modes: a. On a riser fastened into a saddle fitting, mounted straight on the lateral. The saddle has to guarantee the vertical position of the riser. b. By means of a tube and a vertical support that allows a certain flexibility in spacing. This type of connection ensures the vertical position of the sprinkler independently of the position of the lateral. c. Directly on a saddle. Couplers have diverse forms like head elbows, "T", angle, etc. Quick bayonet couplers are used for connection of risers to aluminum and plastic pipes, to valves and other diverse water outlets. a. Polypropylene Fig.6.8. On-line Saddles

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b. Aluminum

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7. REGULATION AND CONTROL 7.1 Introduction An important advantage of pressurized irrigation over surface irrigation is the ease and convenience of regulation and control of the given water amount. The most basic level of regulation is accomplished by: a. Selection of competent equipment according to the requirements of water flow capacity and working pressure grade of pipes, water distribution pattern of emitters, etc. b.

Manual opening and shutting of the water flow.

7.2. Supply Pipelines The supply pipeline delivers the water from the source to the irrigated plot. The pipes are made of coated or noncoated steel or plastic materials like P.V.C., Polyethylene, Polypropylene and Fig. 7.1. Water Supply Network fiberglass. The diameter of the supply pipeline ranges from 3” (75 mm) to 14” (350 mm) diameter. The pipes have to resist pressure surges. The working pressure ranges from 8 to 20 bar (80 – 200 m.). Contemporary water supply networks are monitored and controlled by sophisticated equipment that facilitates efficient water supply and billing, when applicable More advanced levels of control employ automatic valves and controllers, pressure and flow regulators, air-release and vacuum valves, check valves, computers and communication devices

7.3. The Control Head The control head is composed of the accessories that manage the irrigation and the fertigation process. A basic control head may contain the valve and a filter, if needed. The more sophisticated control heads Fig. 7.1. Typical Control Head contain a computerized controller, fertilizer injector, pressure regulator, air-release valve, etc.

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7.4. Regulation and Control Devices 7.4.1. Valves Valves control the flow of the water in irrigation systems. Valves are used for on/off control, regulation of pressure and flow rate and the prevention of back-flow. Valves can be operated manually or automatically by means of mechanical, hydraulic or electrical mechanisms. There are diverse types of valves that have been developed for miscellaneous service requirements.

Fig. 7.3. Valve Types 7.4.1.1. Actuators

Valve

Valves can be operated manually or automatically by means of mechanical, hydraulic or electrical actuators.

Fig. 7.4. . Manual Actuators

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7.4.1.2. Globe Valves The globe valve is the most prevailing valve used in irrigation systems. Its name stems from it globular appearance. In addition to on/off tasks, globe valves are used for throttling and flow control. They demonstrate linear flow response to partial closing. They can be kept open in any degree from fully open to fully closed. The globe valve is controlled by a rising-shaft. The construction of the valve drives the water to make two 90° turns when passing throug h the fully open valve. Hence, pressure losses in the globe valve are higher than in a fully open gate and ball valves. Significant pressure loss is the main drawback of this valve type.

a. Schematic View

b. Direct-flow Body

c. Y Body

Fig. 7.5. Globe Valve

The major components of globe valves are: a. b. c. d. e.

The body. The bonnet. The valve seat and valve plug, or trim. The valve spindle (stem) which connects to the actuator. The sealing assembly between the valve stem and the bonnet.

The principal pattern of globe valve operation is the perpendicular movement of the disk away from the seat. When the disk approaches gradually to the seat ring, the valve is gradually closing. This way of work provides the globe valve good throttling capability for flow regulation. Generally, globe valve yields much less seat leakage than gate valves. The disk-to-seat ring contact is better at right angle and that ensures the tight sealing in shut-off mode. 7.4.1.2.1. Types of Globe valves Globe valves are manufactured in three forms: a. Line valve with straight flow pattern – The connections (flanges or threads) are along the same line. b. Y valve - the connections are in the same line, however the valve disc and the valve plate together are at an angle and the outward shape is of the English letter “Y.” c. Angular valve – The inlet and the outlet have a 900 angle between them.

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Fig. 7.6. Angular Valve

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Most globe valves are built with a single seat. In large globe valves, delivering high volume of water, much force is requested on the actuator for shut-off. If that force is not available (with some electric or hydraulic actuators) a modified double seat valve is requested.

Fig. 7.7. Single-seat Globe Valve

Fig. 7.8. Double-seat Globe Valve

Adapted from Control Valves by Spirax Sarco

Adapted from Control Valves by Spirax Sarco

The double-seat valve has two valve plugs on a common spindle, with two valve seats. The valve seats can be kept smaller and the forces are partially balanced. Although the differential pressure is trying to keep the top valve plug off its seat, it is also trying to push down and close the lower valve plug, so, the force needed for shut-off is smaller than in single-seat valve. Globe valves are built from bronze, cast iron, steel and plastic materials. They are operated by manual or hydraulic actuators. 7.4.1.2.2. Advantages of Globe Valves a. Long service life. b. Very little valve lift is required to attain full flow (unlike gate valves). c. A change in direction of the fluid flow can be done (unlike gate valves) in the angular valve type. 7.4.1.2.3. Drawbacks of Globe Valves a. b. c. d. e.

High head losses caused by the diverted water flow. Large valves require considerable power to operate. Relatively heavy weight compared with other valves with the same flow rating. Large opening necessary for the disk assembly. Cantilevered mounting of the disk to the stem.

7.4.1.3. Angle and "Y" Valves Angle and "Y" valves have less pressure losses than direct-flow globe valves. In the angle valve there are fewer angles compared to the globe valve and the water makes only one 90° turn. In the "Y" valve the water has t o turn twice, as in the globe valve, however, the angles are of 45° only. The flow path is nearly as free as in the gate valve.

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7.4.1.4. Gate Valves The gate valves are used mainly for on/off service. They are not suitable for gradual opening and closing tasks. A disk or wedge attached to the valve spindle regulates the water flow. The common type has a risingspindle that facilitates visual indication how far the valve is open, since the threaded portion of the a. Side View b. Cutaway spindle is exposed. Fig. 7.9. Gate Valve The on/off action is slow. Faster action can be achieved by sliding the spindle up or down with support of a mechanical lever. Since most of the shut-off activity takes place when the valve is almost closed, the flow control profile is not linear. That poses difficulties to regulate the water flow in a partially open position. 7.4.1.5. Ball Valves The ball valve is compact and employs a spherical flow control element. It is operated in 90° rotations. When fully opened, the b all valve has a full flow pattern with minimum head losses. Due to the non-linear flow nature in partial closing, ball valves are used only for on-off tasks and not for flow regulation unless specifically designed for throttling.

a. Side View

b. Diagonal View

Fig. 7.10. Ball Valve Cutaway

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7.4.1.6. Butterfly Valves In a butterfly valve, the flow-control element is a disk pivoted on an axis in the valve casing. The disk is turned parallel to the flowing water when the valve is fully open, resulting in small friction losses. Butterfly valves are simple and compact, and have good throttling capability. The flow response to the shut-off of the flow control element is not linear.

a. Cutaway

b. Main Components

Butterfly valves offer Fig. 7.11. Butterfly Valve economy, particularly in larger sizes and in terms of flow capacity per invested money. Big butterfly valves require large or high-output actuators (if are actuated hydraulically or electrically). Soft-seat assembly is obtained by means of a rubber liner or by an adjustable soft ring in the body or on the face of the disk. 7.4.1.7. Piston Valves Piston valves have a piston-shaped closure member that intrudes into or withdraws from the seat bore. The sealing takes place between the lateral faces of the piston and the seat bore. A fluid-tight contact between these faces is attained by a packing that forms part of the valve bore or the piston. When the valve is being opened, flow cannot start until the piston has been completely withdrawn from the seat bore. When the valve is being closed, the piston tends to wipe away any solids that had been deposited on the seat. Piston valves may handle fluids that carry solids in suspension. If damage occurs to the seating, the piston and the seat can be replaced on the place.

Fig. 7.12. Piston Valve Like globe valves, piston valves allow good flow control. If precise flow adjustment is required, the piston may be fitted with a needle shaped extension. Piston valves are also used for stopping and starting flow when flow resistance due to tortuous flow occurs. 7.4.1.8. Diaphragm Valves Diaphragm valves are flex-body valves in which the valve is composed of a rigid and flexible sections. The flexible section is consisted of a diaphragm which, in connection with an actuator, represents the closure member. In diaphragm valves the flow passage is not obstructed by moving parts and is free of crevices.

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The seat is a rigid body section and may consist of: a. A weir across the flow passage, or b. The wall of a straight-through flow passage. The weir in the flow passage is designed to reduce flexing of the diaphragm to a minimum, in order to guarantee long diaphragm life, while providing a smooth and streamlined Fig. 7.13. Diaphragm Valve Components Adapted flow passage. The short stroke of the from Valve Types by Valvias valve permits the use of plastics such as PTFE for the diaphragm. The back of the diaphragm is lined with an elastomer, which supports a uniform seating stress during valve closure. Since the diaphragm area is large compared with the flow passage, the fluid pressure imposes a correspondingly high force on the raised diaphragm. Diaphragm valves with a straightthrough flow passage require a more flexible diaphragm than weir-type diaphragm valves. In weir-type diaphragm valves the water a. Weir Type b. Straight-through is separated from the shaft and shaft Type collar by the flexible diaphragm. The diaphragm is forced against the weir to Fig. 7.14. Diaphragm Valves close the valve. The fully open valve has only small pressure losses.

Fig. 7.15. Diaphragm Valve Working Pattern

7.4.2. Control Valves – Functioning and Actuation In addition to simple tasks of water opening, shut-off and flow throttling, valves accomplish more complicated tasks like: flow-metering, flow and head regulation, backflow prevention, air-release from the pipes, fertilizer injection, filter flushing, etc.

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Since the mid-fifties, many valves are controlled by programmed controllers and computers. The operation instructions actuate the valves by means of hydraulic or electric actuators. There are also small diameter control valves that are actuated mechanically by the inherent water flow in the valve

Fig. 7.16. Control Valves Actuators These control valves are combinations of valves and actuators. The most prevalent valves are of the flexible diaphragm type that is controlled by an electric valve (solenoid) or hydraulic actuator. Piston valves are used in smaller scale. Power to the actuators is transmitted as an electrical current through wires, through wireless devices or as hydraulic pressure through small diameter tubes. The controllers are classified as normally open (NO) and normally closed (NC) groups. Normally Open means that the valve remains open when the power source is off. The normally closed type remains closed when the power source is off. The normally closed type is safer since when the power supply is impaired, the water is closed. On the other hand, this type has greater pressure losses. 7.4.2.1. Electric Control of Hydraulic Valves In many cases, the driving power of the control element is hydraulic pressure that is activated by the electrical current delivered to the actuator. The flow control element can be in the form of a piston that shuts and opens the flow path in the valve. The piston actuator can also serve as a flow regulator. 7.4.2.1.1. Solenoids The solenoid valve, which is commonly used in irrigation systems, employs an electromagnetic force to drive the piston directly or to activate the piloting action that opens the valve. The conversion of electric pulses into mechanical energy by which the actuator closes or opens the water is done by means of solenoids. Solenoid actuated valves provide for automatic open- Fig. 7.17. Cutaway of Solenoid Valves close valve positioning. Most solenoid actuated valves have a manual override that

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allows manual operation of the valve. Solenoids position the valve by attracting a magnetic slug attached to the valve stem. In single solenoid valves, spring pressure acts against the motion of the slug when power is applied to the solenoid. These valves can be arranged such that power to the solenoid either opens or closes the valve. When power to the solenoid is removed, the spring returns the valve to the opposite position. Two solenoids can be used in one valve to apply both opening and closing by switching power to the appropriate solenoid. Single solenoid valves are termed fail open or fail closed depending on the position of the valve when the solenoid is de-energized. Fail open solenoid valves are opened by spring pressure and closed by energizing the solenoid. Fail closed solenoid valves are closed by spring pressure and opened by energizing the solenoid. Double solenoid valves typically fail "as is." That is, the valve position does not change when both solenoids are de-energized. Modern solenoid valves offer fast operation, high reliability, long service life, and compact design.

a. Fail-closed (Normally Closed)

b. Fail-open (Normally Open)

Fig. 7.18. Scheme of Solenoid Operation

Fig. 7.19. Fail-closed (NC) Solenoid Valve – Components and Working Pattern In one working procedure, the solenoid is acting directly on the main valve. In other cases, a small, fully functioning solenoid valve known as a pilot is used to actuate a larger valve. While the second type is actually a solenoid valve combined with a

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hydraulically actuated valve, they are sold and packaged as a single unit referred to as a solenoid valve. Piloted valves require much less power to be activated, but they are noticeably slower. Piloted solenoids usually need full power at all times to open and stay open, where a direct acting solenoid may only need full power for a short period of time to open it, and only low power to hold it open.

a. Blow-out

b. Working Pattern

Fig. 7.20. Hydraulic Control Valve 7.4.2.2. Hydraulic Control of Valves The structure of a hydraulic controller or actuator is similar to that of the electrical control valve but the power is transmitted by a pressure change above the diaphragm or piston actuator. This change of pressure is transmitted through the hydraulic control tubing or by partial diversion of water flowing through the valve. Most of the hydraulic control valves are normally open. Functionally, hydraulic valves, like the electrical ones, fall into two categories: Normally Open (N.O.) and Normally Closed (N.C.). a. Normally Open (N.O.) valve stays open until the control chamber is filled with water under system pressure. When the chamber is full, the valve shuts-off. b. Normally Closed (N.C.) valve is kept closed by the water pressure in the mainline. In case of a rupture in the command line, the closure is secured by pressure of a spring. The valve is opened when a tiny valve at the top of the control chamber opens, releasing water from the control chamber into the atmosphere. Normally closed hydraulic valves have higher head losses, but they are safer to use, as the valve remains closed even if the command tube is torn or plugged.

7.4.3. Check-valves Check valves are used to prevent the back-flow of water in irrigation and water supply networks. The control element has a variety of forms: ball, disk lift, tilting disk, flipper or a swinging disk. The water passage is kept open by the pressure of the water flowing in the ordinary direction. It blocks the passage for back-flow by the gravity force or by spring action when the pressure downstream is higher than upstream. The pressure caused by back-flow or the weight of a water column in the pipe presses the control element against the seat to seal the passage and prevent flow in the reverse direction. 58

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a. Check-valve Fig. 7.21. Check Valves

b. Check-valve Cross-section

c. Dual Back-flow Check-valve

7.4.4. Pressure Relief Valves

Fig. 7.22. Pilot-controlled Hydraulic Pressure Relief Valves Pressure relief valves protect the irrigation network from excessive pressure. They are opened quickly and release small amounts of water to relieve excess pressure in the system. They can be closed by means of a spring-loaded disc or hydraulic pressure. In some types of valves, the spring can be adjusted to a predetermined pressure limit. Excess pressure partially opens the valve and releases some water. Fast Pressure Relief Valves are automatic control valves designed to provide a solution to the typical problems associated with spring loaded relief valves when constant drifting of relief adjustment occurs. The valve is comprised of accurate relief pressure setting that remains constant, opening to full capacity on minimum pressure rise in the pipe line. Regulated rate of closure provides smooth closure without causing pressure surges.

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The Pilots can be grouped to 3 sets: 7.4.4.1. Pressure Reducing Pilot Valve It is a direct acting pilot valve, actuated by a pressure responsive diaphragm, which seeks to reach equilibrium between hydraulic and set spring forces. When used in a pressure reducing circuit, The pilot-modulate closes as downstream pressure rises above set point. An internal restriction device acts as an upstream flow restrictor. 7.4.4.2. Pressure sustaining pilot valve This is a 2-way direct acting pilot valve, actuated by a pressure responsive diaphragm, which seeks to reach equilibrium between hydraulic and set spring forces. 7.4.4.3. Fast Pressure Relief Pilot Valve This pilot integrates all principal functions of a 2-Way control circuit in a single assembly. It is a direct acting pilot valve, actuated by a pressure responsive diaphragm, which seeks to reach equilibrium between hydraulic and set spring forces. The pilot opens as upstream pressure rise above set point.

Fig. 7.23. Pilot Valves

7.4.5. Pressure Regulators

a. Pressure Regulator–Blow-out

b. Six Unit Assembly

c. Hydraulic Controlled Pressure Regulator

d. Pressure Regulators of Different Capacities Fig. 7.24. Pressure Regulators Pressure regulators are used where low and constant pressure is necessary for the proper function of pressure sensitive components, such as laterals and emitters. They are used in systems with pressure fluctuations to maintain constant pressure downstream of the regulator. Pressure regulators are also used in harsh topography conditions for equalizing the head in emtters. There are two types of pressure regulators. Simple mechanical devices regulate the pressure against a spring, while

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in the more sophisticated devices the pressure is controlled hydraulically by a diaphragm or piston. Table 7.1. Flow-rate of Spring Actuated Pressure Regulators The pressure regulator’s structure is similar to that of Model Flow-rate – m3/h the diaphragm and springMin. Max loaded relief valve. Low flow-rate 0.11 3.0 The water flow is throttled by the action of a spring at (one spring) 0.8 5.0 the top of the diaphragm (2 Springs) 1.6 10.0 and the counter-pressure of the water on the lower face 2" X 4 (4 Springs) 3.2 20.0 of the diaphragm. The water 4.8 30.0 from the high-pressure side 2" X 6 (6 Springs) of the valve is diverted into 3" X 10 (10 Springs) 8.0 50.0 the chamber above the diaphragm to compensate for the compression of the spring as the upstream pressure changes. This action throttles the controlling valve and keeps the pressure at the preset level.

7.4.6. Air-release Valves Trapped air is a critical problem in irrigation and water supply networks and may cause severe damage to certain components of the system. Air intrudes into the system when pumping is primed or when the water is shut-off by the main valve and the local valves remain open. The air enters through the emitters into the drained network. At the start of the irrigation event, the flow of air through the water-meter may bias the metering and in extreme cases may heat and melt the impeller blades. Another effect of trapped air in pipelines is the water hammer caused by the compressed air that may burst the pipes if the pressure surge surpasses the working pressure of the system. Prevention of trapped air damage can be attained by the use of airrelease valves. The valves should be installed in the higher points in the irrigation system, where the trapped air is accumulating in the pipelines.

Fig. 7.25. Cross Section of Air-release Valves

The air-release valve acts by means of a float. When the pipeline is empty or partially full with water, the float is lying down leaving the orifice in the top of the casing open, enabling the flow of air outside and inside. After the system had been filled with water, the float takes its upper position and seals the aperture. There are two basic types of air-release valves:

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7.4.6.1. Kinetic Air Valve This valve is designed to release large amounts of air under low pressure. It is useful at the beginning of the irrigation event when large amounts of air have to be released from the system in a short time. It is also used to enable the high volume back-flow of air into the network after the water shut-off, in order to avoid a vacuum in the pipelines. This valve is not functional at high pressure conditions, when the system has been completely filled with water. 7.4.6.2. Automatic Air Valve This valve functions in low as well as in high-pressure conditions, but it can release only small volume of air. Its main function is to release the small amounts of air that are liberated from the water due to changes in temperature and pressure during the irrigation term. 7.4.6.3. Combined Air Valve This valve incorporates the two air valve types in the same housing and can fully answer the changing demands for air-release from irrigation networks as well as suction of air when water is shut-off.

7.4.7. Atmospheric Vacuum Breakers These are small devices, ½” – 1” in diameter that break the vacuum at water shut-off and do not allow air to escape from the system when water drains from the irrigation system and the pressure in the pipelines falls below the atmospheric pressure. Air relief valves introduce air into the irrigation system when its pressure equals or falls below the atmospheric pressure and function as vacuum breakers.

7.5. Valve Capacity Water flowing through a valve looses energy by the friction with the valve b. Non-flow State walls and its other components. a. Flow State When the free passage cross- Fig. 7.26. Atmospheric Vacuum Breakers section area is larger, wall smoothness is higher and the bends in the flow way are fewer, the capacity of the valve will be higher. By convention, the flow factor (Kv) relates to the hourly discharge that causes head-loss of 10 m. (1 atm). Where: Kv – Flow Factor (m3/h at 1.0 bar pressure drop) (Eq. 7.1) Q – Flow-rate (m3/h) Dp – Pressure drop (bar) S – Specific gravity of the fluid (for water = 1.0)

7.6. Automation 7.6.1. Overview In modern irrigation systems, automation is an essential constituent of the operating system. It saves manpower and facilitates precise and on-time application of water and nutrients.

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Automation relies on four basic components: sensing and measuring devices; control and regulation appliances; input and output tools; and communication between the different components. Time and quantity controllers are the two basic tools of automation. 7.6.1.1. Classification Automation systems can be classified according to the extent of control: a. P o in t automation means an automatic device mounted directly on the valve, exclusively controlling this valve with no relevance to other valves or systems. b. L o c a l automation: Several valves in the plot that are controlled and coordinated by one unit. c. Ce n t ra l automation: A number of local automation units that are connected to and controlled by a main central unit. 7.6.1.2. Functions Automation can be activated at diverse levels of sophistication: a. Shut-off of water flow. Water opening is done manually. b. Time-based automatic opening and shut-off of the water. c. Time determined irrigation start according to time, shut-off after a preset water amount had been delivered. d. As above plus feedback and recording of the delivered water amount. e. Control of irrigation combined with fertilizer application (fertigation), with or without recording of water and fertilizer amounts. f. Sequential operation of valves, one after another, in the plot. g. Irrigation control that relies on information obtained from monitors and sensors. E.g.: Temperature, wind, rain, soil moisture, water head etc. h. Control of water sources in correspondence with irrigation demands. i. Integrated control of water sources and irrigation. j. Integrated design and operation and control of irrigation systems.

7.6.2. Flow-meters

a. Waltman Flow-meter

b. Flow-meter Cross-section

Fig. 7.27. Flow-meters

63

c. Flow-meter Output

with

Electric

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The flow-meter is the basic appliance for the monitoring and control of water application in pressurized irrigation systems. It is the only means that facilitate irrigation control in quantitative terms. The common flow-meter consists of a casing containing a horizontal or vertical impeller. The impeller is rotated by the flowing water and transmits its rotational motion to a measuring scale mounted on top of the casing. The scale is calibrated and counts the actual water quantity that passed through the casing. The flow-meter displays the readings of the delivered water amount visually or, by means of an electric output device, sends the information to irrigation controllers, computers or data-loggers.

7.6.3. Metering-valves (Hydrometers) The metering-valve is a combination of a water meter with a hydraulic valve. The desired volume of water to be applied is dialed in. The valve is closed automatically after the assigned volume of water has been delivered. The actuator in the meteringvalve can be of diaphragm or piston type. A diaphragm is less sensitive to dirt in the water, but can be torn in pressure surges and may wear due to chemical degradation.

Fig. 7.28. Hydrometers – Cross-section From Bermad Brochure

The hydrometer can be operated manually or controlled by a remote computer or controller by means of hydraulic, electric or wireless communication.

7.6.4. Control Patterns Two basic types of control patterns that are applied in irrigation systems: a. Open control loop systems that implement only a preset action. b. Closed control loop systems that collect feedback from sensors, make decisions and apply the decisions to the irrigation system. 7.6.4.1. Open-control Loop Systems In open control loop systems, decisions are taken by the operator who presets the controller according to the desired performance. The devices that require external manual intervention are referred to as open loop systems. In time-based open loop control systems, the irrigation duration is preset. The basic control parameters are irrigation timing, intervals and 64

Fig. 7.29. Hydrometer – Manual and Remote-controlled Dial From Bermad Brochure

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watering time-span. A combination of time and amount-control employs the clock to start the irrigation and terminates the irrigation after the preset volume of water has been applied. Open loop control systems are inexpensive, readily available and flexible but require frequent manual resetting to attain efficient water application. 7.6.4.2. Closed-control Loop Systems In a closed-control loop, the operator presets the general layout. The control system makes the decisions when and how much water to apply. Feedback is sent in real-time to the controller from one or more sensor units. Closed loop controllers acquire environmental parameters, such as soil-moisture, temperature, radiation, wind-velocity and relative humidity. The data are compared to the preset program and the decision is made whether irrigation should be applied or not. The decision can be based on the measurement of soil-moisture and calculation of the water consumption of the plants.

7.6.5. Irrigation Timers An irrigation timer is based on a clock unit that activates one or more units of the irrigation system at preset times. Irrigation timers may provide several of the following functions: a. A c l o c k / t i m e r measures the time for the irrigation schedule. b. A c a l e n d a r s e l e c t o r allows presetting the days in which the system has to be operated. c. S t a t i o n t i m e s e t t i n g allows the presetting of start time, day and hour and duration of application for each station. d. M a n u a l s t a r t allows the operator to start the automatic cycle, overriding the preset schedule. e. M a n u a l o p e r a t i o n of each station allows the operator to manually start the irrigation cycle without changing the preset schedule. f. M a s t e r s w i t c h controls the activation of the whole irrigation system. g. S t a t i o n s k i p is used to exclude specified stations from the next irrigation cycle. h. M a s t e r valve controls back-flow prevention equipment automatically terminates irrigation in case of a failure in the system.

and

i. P u m p s t a r t l e a d connects the pump start solenoid to the actuator of each station. Thus the pumping control is synchronized with the irrigation control. The timers can be electromechanical or electronic. 7.6.5.1. Electromechanical Controllers Electromechanical controllers are based on an electrically powered clock and mechanical switching to activate the irrigation valves. They are reliable and are not affected by spikes in the power supply. In case of power outage, the programmed schedule will not be erased. However, the scheduling options are limited, compared with electronic controllers. 7.6.5.2. Electronic Controllers Electronic controllers rely on solid state and integrated circuits to actuate the clock/timer, memory and control functions. Some of these systems are sensitive

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to the trustworthiness of the power supply and to spikes, surges and brownouts. These controllers are modular and contain many options at a relatively low cost. Time-based devices are widely used in home-gardens, nurseries and propagation houses. Irrigation lasts for relatively short periods, and lack of precision in water amount, due to pressure fluctuations, is not crucial. Improved accuracy can be maintained by keeping constant pressure with the combination of a buster pump and pressure regulators.

7.6.6. Computer-based Irrigation Control Systems A computer-based control system consists of a combination of hardware and software that manages both irrigation and fertigation by a closed control loop. The system monitors the measured variables, compares them with the target status, makes decisions about the actions to be taken and carries them out. 7.6.6.1. Sensors A sensor is closing an electrical circuit response to change in a specific measured parameter. There are two basic types of sensors: a. continuous b. discrete. 7.6.6.1.1. Continuous sensors transmit a continuous electrical signal, such as voltage, conductivity, capacitance, or any other measurable electrical current. Continuous sensors are used where values taken by a state variable are required and an on/off state is not sufficient, for example, to measure pressure fluctuations in the system. 7.6.6.1.2. Discrete sensors are basically mechanical or electronic switches that indicate on/off states. Discrete sensors are useful for indicating thresholds, such as the opening and shut-off of devices. They can indicate when a threshold of a state variable has been reached. Examples of discrete sensors are a float switch in a storage tank and a switching tensiometer that detects if soil moisture is above a defined threshold. The variables measured in computer-based control systems are: Flow rate, pressure, soilmoisture, air temperature, wind velocity, solar radiation, relative humidity, electrical conductivity and the pH level of the irrigation water. 7.6.6.2. A/ D Inter face Since computer systems work internally with digits, the electrical signals sent from the sensors have to be converted from analog to digital data. The conversion is accomplished by Analog-to-Digital (A/D) interfaces. Discrete signals resulting from switch closures and threshold measurements are registered in memory. Continuous electrical (analog) signals are converted to binary numbers of the sensed variable. Conversion accuracy is affected by the resolution of the conversion equipment. 7.6.6.3. Computer Types The A/D conversion hardware is directly connected to the computer system. The computer system may be a PC or a dedicated programmed controller. 7 . 6 .6 . 4 . Func ti ons of the Ce ntr a l Com pute r The fast development and price drop of microcomputers enables high sophistication in automatic control of irrigation. The new irrigation computers and controllers use industry standard microprocessors as well as standard memory boards and 66

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terminals. This configuration enhances the integration of irrigation scheduling, operation and control at the same unit. Conditional operation, relating to the feedback information that is transmitted from the local units and from sensing units in the field, is now a common routine, as well as the integrated management of the whole irrigation system, from water source to the last end-valve in the field. 7.6.6.5. Communication Apart from point automation, in which the automation control unit is mounted directly on the end valve, in all other automation systems, a communication link connects sensors with the control unit to the end valve. In some circumstances, a multi-stage communication linking is necessary. Signals between the control unit and the end units can be sent as hydraulic or electric pulses. The electric pulses can be transmitted by wire or wireless. In some circumstances, for short distance, hydraulic communication is advantageous compared with electric communication. There is no need for an external energy source and in hydraulically operated wide-diameter valves; there is no need for conversion of electric signals to hydraulic signals by means of solenoid. The control water tube of 4 - 8 mm. diameter pipe is cheaper than electric cable. The drawbacks of hydraulic communication are topography interference, vulnerability to mechanical damage and air penetration. In the past the length of communication lines was restricted to a few hundred meters. Latelr-on, accessories have been developed that facilitate longer lines and overcome the topographic differences. Another drawback of hydraulic communication is the one-way communication pattern that does not enable transmission of feedback information back to the main unit. Electric pulses can be transmitted by cables or by wireless devices. Cable communications are prone to mechanical damage. Due to cost reduction, improved credibility and elimination of broadcasting interference, the wireless communications are favored on cable communications. Direct operation of the end-valves by electric pulses takes place only in homegardens and nurseries, where valves are usually of small diameter. In widediameter valves the operation of the valve is hydraulic. The electric signal is converted by means of a small solenoid that controls operating water supply to the hydraulic valve. 7 . 6 .6 . 6 . Confi gur a ti on Local automatic systems control the irrigation timetable and the fertigation device. In sequential automatic systems, a main controlling unit is optional. In sequential irrigation, the shut-off of one hydraulic valve sends a hydraulic signal which opens the subsequent hydraulic valve. In more sophisticated systems, the sequence is controlled by a central controller. There are two basic models of wired central automation: a. Star b. Ring 67

Fi g. 7 . 30 . Loca l I r r i ga ti on Contr ol l e r

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7.6.6.6.1. Star Configuration each local unit is connected directly to the central unit. The cable is of the twinwire type that enables the central unit to send signals as well as to supply energy to the field units. If feedback information is required, a triple-wire cable has to be installed. 7.6.6.6.2. Ring Networks All the field units are chain connected in a ring by one cable to the central unit. The cable is of the multi-wire type in which each local unit is connected by two or three wires to the central unit. Another setup is based on twin-wire cable. Both the two cables are connected to each one of the local units. The computer of the central unit is scanning continuously the local units with high frequency pulses, identifying each unit, feeding it with the relevant information and picking up feedback information. In this configuration, the field equipment is cheaper but a high level computer is required. In the last decade, most of the wired communication systems are replaced by wireless ones.

7.6.7. Supervisory Control And Data Acquisition (SCADA) In the last decade, Supervisory Control And Data Acquisition (SCADA) software applications in Water & Irrigation systems are increasingly used. The SCADA system is a remote control and status indicator of the water distribution equipment that provides early warning of system malfunction. When failure occurs there is immediate detection of water leakages and pressure fluctuations. This enables immediate response to changes in demand, maintenance of adequate pressure, flow-rates, pump-functionality and overall system performance.

Fig. 7.31. SCADA Control System Adapted

Adapted from "Motorola" Brochure

Sophisticated SCADA systems support various communication infrastructures:

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a. Radio Communication Channels: conventional VHF (136-174 MHz), conventional UHF (403-470 MHz), 800/900 MHz, Microwave, Digital Radio, Cellular Networks, Satellite Systems, Wi-Fi (WLAN) systems, Spread Spectrum b. Wire Line: point-to-point, multi-drop, auto-answer/dial-up operation over PSTN lines. c. Ethernet (TCP/IP): Direct connection to a 10baseT Intranet that will be provided by the user. d. Serial Communication: RS-232 and RS-485 Communication to an external DTE/DCE device. The use of advanced communication protocols, sophisticated RTUs (Remote Terminal Units), contemporary control center software packages and utilization of the internet, improves the overall performance of the Water Distribution system by providing: a. Enhanced control and monitoring of pump & Fig. 7.32. RTUs Connected to Field-unit (FU) by Cable valve stations (as well Adapted from Motorola Brochure as other stations and output types) b. Prompt access to data for managers and operators, wherever they are located (at a station, the control room or any other place) from the control center’s alarms and reports c. Graphical User Interface (GUI), which provides a user-friendly and intuitive interface with the control constituents. d. Full monitoring and control of field elements (valves, pumps and other I/O status/failures etc) e. Equipment’s operation 1. Water supply conditions 2. Other conditions and controlled elements 3. Reports and historical data f. Water supply (daily, weekly, monthly, yearly, etc.) 1. Water pressure, low, level, quality etc. 2. Pump operation, valve operation, etc. 3. Power consumption (overall/per pump) g. Alarms 1. Pump failures (overload, temperature, etc.) 2. Power supply failures

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3. Sudden pressure changes, water quality variations, etc. Due to the miniaturization of the electronic components, the wireless broadcasters, transmitters and receivers, the recently developed field units are compact and reliable. 7.6.7.1. Field Units The field units are the end points of the automation system. They include RTUs that directly control the valves, fertigation device, etc; or connected to sensors of soil moisture, chemicals in soil solution and climate. Field Units (FU) that can connect several RTUs enable higher level of control. When many RTUs and/or FUs are connected to one control center, Field Interface Unit (FIU) can be used as the communication interface unit between the control center and the RTUs or FUs. It will be located at the control room and connected to the computer/server via a serial line. The FIU communicates with the RTUs and the FUS over the available project’s communication links (radio, line etc). Many types of I/O (Input/Output) modules are available (Digital Input, Digital Output, Analog Input, Analog Output, Mixed Digital and Analog Inputs and Outputs etc.) enabling simple connection to diverse measuring and control devices such as hydraulically or electrically operated valves, water meters, flow and level meters, rain gauges, EC/pH sensors, flushing filters etc., as well as other devices (relays, general alarm contacts, analog sensors etc.) 7.6.7.2. Internet Mediated Communication In the last decade, the internet provided new capabilities for SCADA communication. Using wireless internet communication enable central and local control, monitoring and data acquisition from any point on the globe, without distance limits.

70

Fig. 7.33. Internet Mediated SCADA Network Adapted from Motorola Brochure

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8. WATER TREATMENT AND FILTRATION 8.1. Introduction Irrigation water quality is defined by its physical, chemical and biological characteristics. The introduction pf micro-irrigation, in particular drip irrigation, posed new challenges for water treatment and filtration. The narrow water passageways in the micro-emitters are exceptionally sensitive to irrigation water quality and are prone to clogging. Although the water passageways in conventional sprinklers are much wider than those of the micro-emitters, the utilization of the new developed filters and the adoption of strict water treatment, improved the performance of sprinkler irrigation systems too. Water pumped from ponds, lakes, rivers, streams, canals and dam reservoirs, contains high loads of impurities. Water pumped from sand aquifers contains great amounts of suspended sand. Sand and silt separation is often performed as a pre-treatment in settling ponds and tanks or by vortex sand separators. a. Physical Quality Parameters: 1. Suspended solid mineral particles 2. Organic matter 3. Live zooplankton b. Chemical Quality Parameters: 1. Salt content 2. The concentration of precipitate-forming ions 3. pH level 4. Nutrition elements content c. Emitter Clogging Factors 1. 2. 3. 4.

Particulate matter Biological living organisms and their debris Chemical precipitates Combinations of the above mentioned factors

Poor system design and management increase the hazard of emitter clogging. Preventive water treatments against clogging are comprised of sedimentation, filtration and complimentary chemical treatments.

8.2. Particulate Matter Sprinklers are prone to clogging by relatively big solid particles but suspended organic matter can stuck to some components and upset the rotating motion. Microemitters are clogged by particles of sand, limestone and other debris too large to pass through the narrow water passageways. Clogging may also occur when small particles stick together to form larger aggregates. Even tiny particles such as suspended clay, which would not cause problems as discrete particles, can initiate clogging if they flocculate to form larger aggregates. Suspended sand particles in the water can cause wearing of the shaft and metallic nozzles in sprinklers.

8.3. Biological Substances Emitters can be clogged by particles of organic matter that block the water passageways. Clogging may be induced by secretions of organisms such as algae and microscopic bacteria. Certain algae are small enough to pass through filters and 71

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emitter passageways as discrete entities, but may flocculate in pipelines to form aggregates large enough to clog emitters. Bacteria are small and do not cause clogging; however, they can precipitate compounds of iron, sulfur and other chemical secretions that clog the emitters. Some bacteria secrete slime that acts as an adhesive platform for the buildup of clay, algae and other small particles into bigger aggregates. Iron and sulfur bacterial slime is a widespread problem. Iron-precipitating bacteria are nourished by the dissolved ferrous iron in irrigation water. These bacteria stick to the surface of suspended soil particles and oxidize the dissolved iron. The oxidized iron precipitates as insoluble ferric iron. In this process, a slime called ochre is created and stick with other substances in pipelines to clog the emitters. Specific bacteria that oxidizes hydrogen sulfide and convert it into insoluble elemental sulfur, creates sulfur slime, a white or yellow stringy deposit formed by oxidation of hydrogen sulfide that is present mainly in shallow wells. The slime clogs emitters either directly, or by acting as an adhesive agent for other small particles.

8.4. Chemical Precipitates Chemical clogging of emitters frequently results from precipitation of one or more of the following cations: calcium, magnesium, iron and manganese. These materials may precipitate from the solution and form scales that partially or fully clog emitters. Precipitation can be triggered by changes in pH, temperature, pressure, water flow velocity and reaction with ions that are injected into the irrigation water by fertigation as well as by exposure to atmospheric oxygen. Table 8.1. Relative Clogging Potential of Micro-emitters by Water Contaminants Water characteristic pH TDS (Total dissolved solids) - ppm Suspended solids - ppm Manganese - ppm Iron - ppm Hydrogen sulfide - ppm Bacteria population - per ml

Minor 50,000

After Blaine Hanson. 1997

8.5. Water Hardness Water containing substantial concentrations of Ca++, Mg++ and Fe++ is regarded as “hard water”. Hard water can precipitate poorly-soluble carbonates in the irrigation system. Water “hardness” is expressed as a calcium carbonate concentration equivalent in mg/l units. Hardness is calculated by measuring the content of the above mentioned Cations, summing up their concentrations expressed in meq/l and multiplying by 50 (the equivalent weight of calcium carbonate). Example: Calcium equivalent weight ≈ 20 Calcium concentration in the water: 120 mg/l ≈ 120/20 = 6 meq/l Magnesium equivalent weight ≈ 12 Magnesium concentration in the water 60 mg/l ≈ 60/12 = 5 meq/l Total 11 meq/l 72

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Water hardness = 11 meq/l X 50 = 550 mg/l Calcium Carbonate Equivalent The most prevalent precipitate from hard water is calcium carbonate. However when fertigating with fertilizers that contain phosphorous and sulfur, calcium phosphate and calcium sulfate (gypsum) may also precipitate. Similar reactions precipitate magnesium bi-carbonate.

8.5.1. Iron and Manganese in Water Iron is often dissolved in groundwater as ferrous bi-carbonate. When exposed to air, or to activity of iron bacteria, the iron is oxidized, precipitates and can plug microemitters. Manganese is occasionally present in irrigation water, but at lower concentrations and with lower activity as a clogging factor than iron.

8.6. Biochemical Oxygen Demand (BOD) Organic matter suspended in the water is decomposed by microorganisms that consume oxygen along the process. The quantity of oxygen consumed by these organisms in breaking down the organic matter is designated as the Biochemical Oxygen Demand or BOD. BOD is a consistent indicator for clogging hazard of microemitters by suspended organic matter. Raw sewage and low-quality reclaimed water have high levels of contamination and consequently high BOD values.

8.7. Filtration Because of the narrow water passageways in microemitters and the slow water-flow velocity, micro irrigation systems are susceptible to clogging much more than conventional sprinklers. As mentioned before, prevention of clogging necessitates high-level filtration and complimentary chemical and physical water treatments.

8.7.1 Screen (Strainer) Filters Screen filters' features are defined by filtration degree, filtration surface area and filtration ratio. 8.7.1.1. Filtration degree is designated in microns or mesh number. The filtration degree in microns indicates the diameter of the biggest ball-shaped particle that can pass between the screen wires. 8.7.1.2. Mesh number counts the number of wires along a 1" (25.4 mm) length of the screen. The two concepts are not fully inter-convertible.

Fig. 8.1. Screen Filter From Netafim Brochure

Perforation width may differ between two screens with the same mesh number due to different wire thickness. Approximate conversion from one indication mode to another is done by rule of thumb: mesh number x microns ≈ 15,000. Example: Screen perforation 120 Mesh. What is the filtration degree in microns? 15,000/120 = 125 micron 73

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When selecting the filtration Table 8.2. Screen Perforation Examples degree, the dimensions of the Mesh No. Hole size – Wire thickness water passageways in the microns microns emitter and the character of 40 420 250 water impurities should be 50 300 188 considered. When the 80 177 119 impurities are suspended 100 149 105 inorganic solids (sand, silt, 120 125 86 chemical precipitates), the 155 100 66 maximum perforation diameter 200 74 53 should be 25%-30% of the sprinkler's nozzle or the micro-emitter's water passageway diameters. When the impurities are organic and biological materials, the maximum perforation diameter should not exceed 10%-20% of the water passageway diameter in the emitters. Screen filters are most suitable for water with inorganic impurities, while high loads of organic and biological impurities commit other types of filters since the impurities may quickly clog the screen. There is wide selection of screens. In selecting screen type, water quality and emitter water passageway structure have to be considered. Perforated steel screen is the strongest structure but its effective filtration ratio is the lowest. It Perforated Steel Wedge Wire is used mostly in filters that are installed to protect the Fig. 8.2. Screen Patterns pumping unit when the pumped water contains coarse soil particles, gravel and stones.

Woven Wire

Woven wire is the most prevalent type of screen. Its effective filtration ratio is the highest, but the structure is the least robust. Wedge wire strength is intermediate and it is only rarely used. One of the main disadvantages of screen filters is the fast accumulation of dirt on the screen's surface. The accumulated dirt increases the head losses and may trigger collapse of the screen. Monitoring the pressure difference between the filter inlet and outlet is necessary to scrutinize excessive dirt accumulation on the screen. The filter has to be flushed and cleaned when the pressure difference between inlet and outlet approaches 5 m. (0.5 bar).

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Fig. 8.3. Head Losses in Clean Screen Filters Adapted from "Odis" brochure

8.7.2. Disc Filters Disc filters are suitable for filtration of water containing mixed, inorganic and organic impurities. The casing is made of metallic or plastic materials. The filtering element is a stack of grooved plastic rings, tightened firmly by a screw on cap or by a spring that is compressed by a water-piston. Water is filtered as it flows from the perimeter into the stack inner space through the grooves. The intersections of the grooves provide in-depth filtering. Coarse particles are trapped on the external surface of the stack. Finer particles and organic debris stick to the inner grooves. Disc filters have a higher dirt-retention capacity than screen filters. The definition of the filtration degree is identical to that of screen filters and is usually indicated by the color of the discs.

Fig. 8.4. Disc Filter

8.7.3. Media Filters Media filters protect emitters when using water with a high organic load from open water bodies or reclaimed water. Wide-body (0.5 - 1.25 m in diameter) media containers are made of epoxy-coated carbon steel, stainless steel or fiberglass.

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Fig. 8.5. Media Filters The filtering media are of 1.5 - 4 Table 8.3. Sand Particle Size and Mesh Equivalent mm size mm basalt, gravel, Sand No. Effective sand Mesh equivalent crushed granite particles or fine size – mm range silica sand of 0.3 – 1.5 mm Crushed Silica 12 1.1. – 1.2 80 - 130 effective size. The organic Standard Sand 0.9 – 1.0 100 - 140 impurities adhere to the surface 6/20 of the media particles. The Crushed Silica 16 0.6 – 0.7 155 - 200 accumulated dirt should be U.S. Silica 80 0.6 – 0.7 160 - 200 back-flushed routinely in order Crushed Silica 20 0.28 170 - 230 to eliminate excessive head losses. The filtration degree is defined equivalently to that of screen and disc filters.

8.7.4. Sand Separators High loads of sand and other solid particles should be removed before getting to the main filtration system. There are two methods of sand separation. The traditional practice was based on sedimentation of solid particles by slowingdown water flow in closed settling tanks or open basins. Closed tanks conserve the water

Fig. 8.6 Sand Separator - Working Pattern

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pressure while the use of open settling basins requires re-pumping of the treated water into the irrigation system. Centrifugal (vortex) sand separators deposit sand and other suspended particles heavier than water by means of the centrifugal force created by tangential flow of water into a conical container. The sand particles thrown against the container walls by the centrifugal force settle down and accumulate in a collecting chamber at the bottom. The collector is washed out manually or automatically. Clean water exits through an outlet at the top of the separator. Each separator has an optimal flow-rate range in which the most of the suspended particles are removed without excessive head-losses. At lower flow-rates, more sand remains suspended in the water.

Fig. 8.7. Hydro-cyclone Sand Separator – Head-losses and Optimal Flow-rates From "Odis" brochure

8.7.5. Filter Characteristics 8.7.5.1. Reliability Disc filters' reliability is higher than that of screen filters. Collapse of the filtration element is uncommon. In screen filters, the screens are prone to be ripped due to corrosion and to collapse by pressure surges. The screen-supporting frame has to withstand these pressure surges. 8.7.5.2. Capacity and Head-losses Water loses pressure as it flows through a filter. The extent of head-losses depends on the filter design, filtering degree, flow-rate and the level of dirt accumulation. Normally, for a specific filter type and size, the finer the filtration degree, the lower the nominal discharge. This is due to faster dirt accumulation and higher head-losses. 8.7.5.3. Key Screen Filter's Attributes 8.7.5.3.1. Diameter: Designates the diameter of the water inlet and outlet. 8.7.5.3.2. Filtration Area: The total surface area of the filtration element. The required filtration area for moderately dirty water is 10 - 30 cm2 for each 1 m3/h of flow-rate for sprinkler irrigation and 25 - 60 cm2 for micro-emitters 8.7.5.3.3. Perforation Area: The total open area of perforations.

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8.7.5.3.4. Effective Filtration Ratio: The ratio between the perforation area and the filtration area. 8.7.5.3.5. Filter Ratio: The ratio between the perforation area and the inlet crosssection area. The higher the above mentioned parameters, the higher the filter capacity. The nominal capacity of other types of filters is defined according to the permissible headlosses. Table 8.4. Nominal Filter Capacity – Examples Make Odis Arkal Arkal Arkal Amiad Amiad Odis Netafim Netafim

Filter type & diameter

Filtration grade microns 60-400 100-400 75 25 80-300 100-250 60-400 60-200

2” screen 2” disc 2” disc 2” disc 3” screen 3” disc 4” screen 4” gravel 6” sand separator

Capacity m3/h 15-25 25 16 8 50 50 80 60-120 140-230

Nominal filter capacity designates the flow-rate at a head loss of 2 m (0.2 bars) in a clean filter. As dirt accumulates, the head loss increases. Filter cleaning is required when the head-loss amounts to 5 m. (0.5 bars). As mentioned before, a minimalhead-loss of 1.5 m (0.15 bar) is required for acceptable sand separation by hydrocyclone sand separators but the recommended head-loss range in these separators is 2.5 - 5 m (0.25 - 0.5 bar). Dirt accumulation capacity is the lowest in screen filters, higher in disc filters and the highest in media (sand and gravel) filters.

8.7.6. Flow Direction The direction of the water flow through the filtration element is an important feature. In disc filters, water flows from the perimeter inwards. This pattern exposes to the flowing water the greater external surface area of the disc stack that is able to retain a much greater quantity of coarse particles than the smaller inner surface area. In screen filters, flow from inside outside is more suitable for self-cleaning mechanisms and is less vulnerable to screen collapse by pressure surges. Some models of screen filters have two filtering elements: an external preliminary coarse strainer that traps the coarse particles, and an internal finer screen for final filtration. In these Filters, flow direction is from the perimeter inwards. Some filter designs include nozzles in the inlet to induce tangential flow of water that drives the dirt to the distal end of the filter where it is flushed-out intermittently or trickles out continuously. In media filters, water enters from the top and exits from the bottom after crossing the filtering media that lies on a perforated plate. Back-flushing is accomplished in the opposite direction – from the bottom upwards. To facilitate proper back-flushing, the media fills no more than 2/3 of the tank volume, so that it can be lifted and agitated during the back-flushing process.

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8.7.7. Filter Cleaning As mentioned before, filters have to be cleaned routinely before contaminants accumulation causes excess head losses or may cause collapse of the filtration element. Filters can be cleaned manually or automatically. 8.7.7.1. Manual Cleaning Conventional screen filters have to be disassembled. Each component has to be flushed. The integration of the screen and its supporting frame has to be checked. Torn screens have to be replaced. Some screen filters are equipped with mechanism that enables manual cleaning without disassembling the filter.

a. Disassembled b. Rotating Brushes (BrushAway) Screen Filter

c. Rotating Suction Nozzles (ScanAway)

Fig. 8.8. Manual Cleaning of Screen filters From Netafim and Amiad Brochures

Fig. 8.10. Continuous Flushed Circulatingfilter

Fig. 8.9. Manual Hose Flushing of a Disc-filter

In disc filters, the discs, that are fastened in the stack have to be relieved and separated from each other, prior to flushing. The best way of cleaning conventional disc filters is to flush the stack with water from a hose, after the release of its fastening knob. The separation of the discs by the water flow enables the removal of the impurities from the discs' grooves. 8.7.7.2. Automatic Flushing and Cleaning Diverse automatic cleaning mechanisms have been developed. The cleaning process is either continuous or pulsated. Continuously self-flushing screen filters maintain a flow of filtered water without the build-up of head losses. The dirt is continuously removed from the screen by a 79

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tangential, spiraling downward water flow, which flushes the debris into a collecting chamber at the bottom of the casing. The accumulated dirt is drained manually, constantly by a bleeder, or is automatically released when a preset water differential between the water inlet and outlet had been built. In most of them the pressure differential is monitored and the self-cleaning process is activated when the preset pressure differential had built-up. The intervals between flushing events may be also controlled by a timer.

a. High-capacity Automatic Filter

b. Compact Automatic Filter

Fig. 8.11. Automatic Screen Filters with Scanning Nozzles The cleaning process is carried on for a preset time length. The cleaning and flushing mechanism is powered by the inherent pressure of the system or by an electric motor. Rotating brushes or sucking nipples clean the screen. For coarse screens, of over 200-micron filtering degree, brushes are sufficiently efficient while for finer screens under 200 microns, cleaning by rotating suckers is more effective.

Fig. 8.12. Automatic Flushing of Disc-filter Adapted from "Arkal" brochure Automatic flushing of disc filters requires the release of the discs in the stack. The Spin-Kleen mechanism combines release of the stack tightening-screw, backflushing by water counter-flow, and spinning of the relieved discs by the water stream that flushes the dirt from the grooves to a draining valve that opens automatically. 80

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Media filters are flushed automatically by backflow from the bottom that floats the accumulated dirt and releases it out through the drain valve on top. The reverse-flow is activated automatically when the preset pressure differential has been reached. Automatic flushing of media and disc filters requires counter-flow of filtered water. To meet this requirement, filters operate in arrays and the flushing of filters is sequential, one after another.

Fig. 8.13. High-capacity Media-filter Array

Fig. 8.14. Back-flushing of Media-filters

8.7.8. Filter Location Sand settling tanks are installed ahead of the pump while sand separators are installed just downstream of the pump. In highly contaminated water, multi-stage filtration is required. An automatic screen, disc, media filter or a filtration array of several filters should be installed at the pumping site or the main control head. Backup control screen or disc filters should be installed at the head of each irrigating sector. With moderately contaminated well water, one filtration stage at each zonal valve may be sufficient.

8.8. Supplementary Water Treatments With micro-emitters, in addition to filtration, complementary chemical treatments should be performed on the irrigation water to prevent the clogging of the emitters. Oxidation and acidification are the prevalent complementary treatments. Oxidation decomposes organic matter, prevents formation of slime by sulfur and iron bacteria, blocks development of algae and eliminates infestation by pathogens. Acidification eliminates chemical precipitation and dissolves in-built precipitates in the irrigation system.

8.8.1. Chlorination Chlorine, the common oxidizing agent appears in three forms: a. Solid tablets containing 90% chlorine. b. Liquid sodium hypochlorite (NaOCI) containing 10% chlorine. c. Gaseous chlorine. This form is cheap and efficient but is unsafe in use and commits strict pre-caution measures in application. 81

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When ferrous iron is present in the water, one ppm (part per million) of chlorine is required per each ppm of iron to kill iron bacteria and precipitate the iron from the water. When hydrogen sulfide is present, 9 ppm of chlorine are needed per each ppm of sulfur to kill the sulfur bacteria, prevent slime growth and precipitate the sulfur from the water. The precipitates formed in theses processes, must be retained by the control filters at the zonal irrigation control heads to prevent clogging of the emitters. Effective chlorinating decomposes organic materials and blocks the development of algae and plankton in the laterals and the emitters. 1 - 2 ppm of residual chlorine detected at the distal ends of the laterals indicates adequate chlorination. To maintain these residual levels, chlorine concentration in the water at the injection point should range between 3 – 15 ppm, depending on the impurity load and duration of injection. Levels higher than 15 ppm can harm the diaphragms in certain hydraulic valves.

8.8.2. Acidification Acidification of water is required when "hard" water containing high concentrations of bi-carbonates is used for irrigation with micro-emitters. The injected acid neutralizes the transient hardness and immerse calcium carbonate precipitates. Acid can be applied with ordinary fertigation equipment or by a dedicated metering pump. The common acidifying agents are sulfuric, nitric, hydrocloric and phosphoric acids. Chlorination of acidified water is more effective than chlorination of alkaline water, reducing the chlorine requirement. Hence if both chlorination and acidification are done simultaneously, acidification will be applied first, followed by chlorination. Mixing acid with chlorinating agents is forbidden since it can induce a toxic chemical reaction. Commonly, chemical treatments are implemented upstream from the filtration system. The impurity load is reduced and the decomposed material is trapped in the filters. The narrower the water passages in the emitters, the greater the need for chemical treatments. That rule is excluded when, as mentioned before, the oxidation of iron and sulfur bacteria forms solid particles that have to be retained by control filters in the irrigation zonal heads.

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9. FERTIGATION 9.1. Introduction Fertigation is the technology of applying nutrition elements via the irrigation water by injection of fertilizer solutions into the irrigation system. Contemporary fertigation technology emerged at the sixties of the 20th century, following the introduction of commercial drip irrigation. Prior to that era, direct application of nutrition elements to the water had been implemented only in hydroponics growing systems. Later it was realized that crops benefit of fertigation in all the pressurized irrigation technologies and in some circumstances, although rarely, in surface irrigation too. The combined application of water and fertilizers through the irrigation system increases the efficiency of fertilizer utilization, raises yields, improves produce quality and minimizes environmental pollution caused by excess fertilization.

9.1.1 Advantages of Fertigation a. Improved efficiency 1. Uniform distribution with irrigation water 2. Better synchronization with crop demands i. Adjustment of amounts and ratio between nutrients along the growing season 3. Deeper penetration of the nutrients into the soil 4. Avoiding nutrient losses from soil surface b. c. d. e.

Avoiding soil compaction by fertilizer spreaders Avoiding damage to canopy and yield Reduction of fertilizer losses Additional functionality 1. Application of herbicides and pesticides via the irrigation water

9.1.2. Limitations and Risks in Fertigation a. b. c. d. e. f.

Hazard of backflow of nutrient solution into the drinking water supply network Only fully soluble fertilizers are applicable Hazard of corrosion, precipitate-formation and clogging in the irrigation system Use of dangerous acids and inflammable materials Costly investment in accessories and storage installations Incorrect application may cause damage to crop, nutrient losses by leaching beneath the root-zone and contamination of underground water resources g. Hazard of foliage and fruit scorching in overhead irrigation h. Large storage volumes are needed for nutrient solutions

9.2. Technologies of Fertigation A variety of technologies have been developed for injecting fertilizers into the irrigation system.

9.2.1. Patterns of Injection 9.2.1.1. Fertilizer Concentration a. Decreasing along time (Fertilizer tank) b. Uniform – pulsating (piston and diaphragm pumps) c. Uniform – constant (venturi, internal mixing pumps, mixers)

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9.2.1.2. Energy Sources a. Inherent pressure of the irrigation system b. External energy sources 1. Electricity 2. Internal combustion engines 9.2.1.3. Injector Types a. Pressure differential b. Venturi (suction) c. Fertilization pumps

9.2.2. Fertilizer-tank Throttling the water flow in the control head creates pressure differential that diverts a fraction of the irrigation water through a tank containing the fertilizer solution. A gradient of at least 1 – 2 m. (0.1 – 0.2 bars) is required to redirect an adequate stream of water through a connecting tube of 9 – 12 mm diameter. The tank, made of corrosion-resistant enamelcoated or galvanized cast iron, stainless steel or fiberglass, has to withstand Fig. 9.1. Fertilizer-tank From "Odis" brochure the irrigation network working pressure. The diverted water is mixed with solid soluble or liquid fertilizers. When solid fertilizers are used, the nutrient concentration remains more or less constant, as long as a portion of the solid fertilizer remains in the tank. Once the solid fertilizer had been fully dissolved, continuous dilution by water gradually decreases the concentration of the injected solution. 9.2.2.1. Fertilization-tank Advantages a. b. c. d. e. f.

Simple construction and operation Low cost (of small units) Extensive field experience No need of external energy source Good mobility Wide dilution ratio

9.2.2.2. Fertilization-tank Limitations a. b. c. d. e.

Head losses by throttling High cost of large units Non-uniform nutrient concentration along the period of application Fertilizer replenishment is needed prior to each application Integration with automation is problematic

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f. The tank and the accessories have to withstand the mainline operating pressure

9.2.3. Venturi Injector Suction of the fertilizer solution is created by water flow through a constricted passageway. The high flow velocity of water in the constriction reduces water pressure below the atmospheric pressure so that fertilizer solution is sucked from an open tank into the constriction through a small diameter tube.

Fig. 9.2. Venturi Injector

Courtesy "Netafim"

Venturi devices are made of corrosion-resistant substances such as copper, brass, stainless steel and plastic materials. The injection rate depends upon the pressure loss, which ranges from 10% to 75% of the irrigation system's pressure and is determined by the injector type and operating conditions. Venturi devices require extra pressure to allow for the necessary pressure-loss. Maintaining a constant pressure in the irrigation system guarantees uniform nutrient concentration in the irrigation water along the application period. The customary head-losses are above 33% of the inlet pressure. Double-stage Venturi Fig. 9.3. By-pass Venturi Installation injectors have lower pressure-losses downward Courtesy "Netafim" to 10%. The suction-rate depends on the inlet pressure, pressure-loss and the diameter of the suction tube. It can be adjusted by valves and regulators. Suctionrates vary from 0.1 l/h to 2000 l/h. Venturi injectors are installed in-line or on a bypass. In greenhouses, the water flow in the bypass may be boosted by an auxiliary pump. 9.2.3.1. Venturi Suction Injector Advantages a. b. c. d. e. f. g. h.

Simple to operate, easy to install, no moving parts Wide-range of flow-rates (in different models) Low cost of small devices, The solution is sucked from an open tank Good mobility Constant suction-rate (in constant pressure regime) Easy integration in automation Cheap, open to the atmosphere tanks may be used Corrosion resistance

9.2.3.2. Venturi Suction Injector Limitations a. High head-losses b. Sensitivity to pressure fluctuations c. Narrow discharge-range of each model

9.2.4. Injection Pumps Fertilizer pumps are driven by electricity, internal combustion engines, tractor PTO or hydraulically by the inherent water pressure in the irrigation system.

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9.2.4.1. Pump Injectors Advantages a. b. c. d.

Uniform nutrient concentration along the fertigation process Easy control of amount and concentration of the nutrient solution Convenient integration with automation No pressure losses

9.2.4.2. Pump Injectors Limitations a. b. c. d. e. f.

High initial cost Complicated operation Wear of moving components Suitable only with fertilizer solutions Some models need external power source Some models emit surplus driving-water outside

9.2.4.3. Hydraulic Pumps Versatile devices, reliable and feature low operation and maintenance costs. A diaphragm or piston movement injects the fertilizer solution into the irrigation system. Water-driven diaphragm and piston pumps combine precision, reliability and low maintenance costs. 9.2.4.3.1. Hydraulic Pump Types a. Piston pumps b. Diaphragm pumps c. Internal-mixer pumps

Fig. 9.4. Piston (left) and Diaphragm (right) Hydraulic Pumps From "Amiad" Brochure

Fig. 9.5. No-drain Internal-mixer Hydraulic Pump From "Dosatron" brochure

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Fig. 9.6. Piston Pump Installation on Control-head 9.2.4.3.2. Injection Control Hydraulic pumps used in fertigation can be automated. A pulse transmitter is mounted on the pump. The movement of the piston or the diaphragm's spoke sends electrical signals to the controller that measures the delivered volume. Measurement can also be performed by small fertilizer-meters installed on the injection tube. Fertilizer-meter is a modified water-meter, corrosion resistant and precise in measurement of small solution quantities. The controller allocates fertilizer solution according to a preset program. In glasshouses, simultaneous application of a multi-nutrient solution is routine. When the distinct chemical compounds in the fertilizers are incompatible and cannot be combined in a concentrated solution due to the risk of decomposition or precipitation,

Fig. 9.7. Fertilizer Solution Meter with Pulse Transmitter From "Arad" Brochure

Two or three injectors are installed inline one after another, in the controlhead. The application ratio between the injectors is coordinated by the irrigation controller. In high-income crops grown in glasshouses on detached media, the irrigation water is mixed with fertilizers in a mixing chamber (mixer). 9.2.4.3.3. Centrifugal Pumps Centrifugal pumps are used when high capacity is needed or the fertilizer

Fig. 9.8. Mixer Array From "Odis" brochure

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solution is turbid. 9.2.4.3.4. Roller Pumps Roller pumps are used for precise injection of small amounts of a nutrient solution. Their life-span is relatively short due to bearings' corrosion by the injected chemicals. 9.2.4.4. Electric Pumps 9.2.4.4.1 Electric Pumps Advantages a. b. c. d.

Precise and reliable Suitable for extremely low dosage Conveniently integrated with automation Wide range of flow-rates

9.2.4.4.2. Electric Pumps Limitations a. Need of external energy source b. Fails in blackout occasions

Fig. 9.9. Electric Pump Electric pumps are inexpensive and reliable. Operation costs are low and they are readily integrated into automatic systems. A wide selection of pumps is available, from small low-capacity to massive high-capacity pumps. The working pressure is 10 - 100 m. (1 – 10 bars). Electric piston pumps are exceptionally precise and suitable for accurate mixing in constant proportions of a number of stock solutions. Variable speed motors and variable stroke length allow for a wide range of dosing from 0.5 to 300 L/h.

9.3. Injection Site Options:

9.3.1. Injection at the Main Control-head - the most convenient and costeffective alternative.

9.3.2. Injection at Sub-main Heads - a common practice in field crops. 9.3.3. Injection at the Control-head of Each Block – more expensive than the above-mentioned alternatives.

9.4. Control and Automation Dosing patterns:

9.4.1. Quantitative Dosing: a preset amount of fertilizer is injected into the irrigation system during each water application. Injection may be initiated and controlled automatically or manually.

9.4.2. Proportional Dosing: maintains a constant predetermined ratio between the irrigation water and the fertilizer solution. Pumps inject the fertilizer solution in a pulsating pattern. Venturi injectors apply the fertilizers continuously and in constant concentration.

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9.5. Avoiding Corrosion Damage Most fertilizer solutions are corrosive. Accessories exposed to the injected solution should be corrosion-resistant. The injection device and irrigation system must be thoroughly flushed after fertilizer injection.

9.6. Back-flow Prevention Whenever the irrigation system is connected to a potable water supply network, strict precautions should be taken to avoid backflow of fertilizer-containing irrigation water.

9.6.1. Back-siphonage occurs when low pressure in the supply line is created by an excessive hydraulic gradient in undersized pipes in the supply line, a break in the supply line, pump or power failures. 9.6.2. Back-pressure occurs when the pressure in the irrigation system is higher than in the water supply network. This happens when booster pumps are used for pressure increase in the irrigating area or when the irrigated area is topographically higher than the local water supply tank. An atmospheric vacuum breaker can be installed beyond the last valve to allow air entry downstream when pressure falls. A pressure vacuum breaker has an atmospheric vent valve that is internally loaded by a spring. This valve is unsuitable for fertigation systems operated by an external source of energy. Vacuum breakers are effective only against back-siphonage and do not prevent back-pressure. A dual check valve assembly has two check valves in tandem, loaded by a spring or weight. The device is installed upstream from the injection system and is effective Fig. 9.10. Tandem Back-flow Preventer against backflow caused by both back-pressure and back-siphonage. A reduced pressure backflow preventer is also consisted of two internally loaded check valves separated by a reduced pressure zone. When pressure downstream is higher than the pressure upstream, water is released to the atmosphere and does not flow backwards.

9.7. Chemical Aspects of Fertigation a. Interaction between fertilizers and irrigation water b. Interactions between fertilizers 1. 2. 3. 4.

Precipitation Decomposition Antagonism Synergism

Diverse interrelations prevail between chemical agents immersed simultaneously in water. When fertilizer solution is injected into the irrigation water, the cations and anions that compose the fertilizer react with the cations and anions inherent in the water. Some

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reactions may create insoluble compounds that precipitate and may clog filters and emitters. That mostly happens with phosphoric fertilizers injected into calcium and magnesium rich water (hard water) of high pH level. Chelates of iron and manganese may decompose when mixed with acid fertilizers. Other patterns of interrelations are antagonism and synergism between ions. Generally, ions of the same type of electrical charge (+ or -) are antagonistic to each other and compete in absorption and bio-reactions in the plant. For example: high level of potassium induces magnesium deficiency and vis versa. Table 9.1. Electric Charges of Nutrients

Between ions with different sign may exist synergism – positive impact on each other. For example, simultaneous presence of potassium and nitrate in solution increases absorption of both ions.

CATIONS Ammonium Potassium Calcium Magnesium Iron

NH4+ +

ANIONS Nitrate NO3Phosphate H2PO4HPO4= Sulfate SO4= Molibdate MoO4= Borate B4O7=

K Ca++ Mg++ Fe++ Fe+++ Zinc Zn++ Manganese Mn++ Copper Cu++ Sodium Na+ Chloride

The chemical aspects have to be considered when nutrient application with fertigation is scheduled.

9.8. Safety

Many fertilizers are corrosive. Some of them may be toxic, carcinogenic or inflammable. Dealing with fertilizers commits caution measures.

Cl-

a. When dealing with fertilizers, one has to wear protective clothes and to use goggles, gloves and boots. b. When diluting acids, the acid has to be poured slowly into a great amount of water, to avoid heating and boiling of the solution. Water will be never poured into the acid. c. Some of the fertilizers are inflammable. No weeds and garbage are allowed in the injection site and storage vicinity.

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10. FLOW-RATE – WATER HEAD RELATIONSHIP 10.1. Water Head In pressurized irrigation systems, water exists under pressure. The water pressure is a key factor in these systems' performance. For sake of convenience in calculation, the term head, is preferred in dealing with pressure in irrigation systems. Water head is actually the potential (or the free energy) that the water retains to accomplish work. The work done is mostly the delivery of water from one point to another through the irrigation network. The water potential is related to a reference point. By definition, the reference point is the atmospheric pressure at sea level at standard ambient temperature (250C). Pressure can be expressed in different unit systems. Table 10.1. Pressure and Water Potential Units

DEFINITION

UNIT

SUB-UNITS

CONVERSION

Pressure / water potential

Bar

=100 Centibars

0.99 Atm.

Pressure / water potential

Atmosphere (Atm)

≈100 Centibars

1.01 Bar

Pressure / water potential

Kilopascal (kPa)

= 1000 Pascal

0.01 Bar=1 Centibar

Head

Meter

=100 cm

0.1 Atm. ~ 0.1 Bar

Pressure / water potential

PSI

≈0.068 Atm. ≈0.68 m

As mentioned before, for simplicity and convenience in irrigation systems design, the preferred unit system is the dynamic head, expressed in meters (m) height of water column. This unit system incorporates the effects of topography and friction losses in pipes on the dynamic head, at each point of the irrigation system. Water dynamic head can be referred to as the hydraulic potential energy of the water. Water flowing in pipes loses energy by friction with pipe walls and other components of the irrigation system. The friction losses can be classified in two categories: a. Longitudinal Friction Losses (hf): arise from the friction of the water with the pipe walls. The losses accumulate along the pipe. b. Local Losses (ht): are created by the turbulence that occurs by sudden changes in the flow pattern, as in abrupt change in pipe diameter, the flow through a valve or a filter, bends in the pipeline, etc. These losses are local but have to be taken into account and added to the longitudinal losses. The total water head, measured at a specific point of the irrigation system, is composed of three ingredients:

10.1.1. Elevation Head (z) Elevation head is derived from the topographic position, the relative height of a given point above or below a point of reference. For example, if the main valve in the plot is positioned 5 m above the distal end of the plot, the measured static (elevation) head at the distal end will be 5 m higher than the static head measured at that valve. Static head is the pressure measured at a point in the water system when no water flow is taking place. 91

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10.1.2. Dynamic Head The dynamic head is the head measured in a certain point in the irrigation system, when water flow. The requested total dynamic head is the sum of the operating pressure, the friction head losses within the irrigation system and the pumping lift, if applicable. In a properly designed irrigation system, the total dynamic head should be the same in each concurrently irrigating subunit to ensure uniform water distribution in the irrigated sub-plots.

10.1.3. Velocity Head Flowing water has kinetic energy (velocity head) represented by V2/2g where V is the velocity expressed in m/sec and g is the gravitational constant 9.81 m/sec2. The velocity head can be expressed in m. units. Squaring V by itself (V x V = V2) results in units of m2/sec2 which divided by g in m /sec2 units, expresses velocity head in the same units as dynamic head, namely the height of water column in m. units.

10.2. Head Losses As mentioned before, head-losses result from friction between the pipe walls and water as it flows through the system. Obstacles - turns, bends, expansions and contractions, etc., along the water flow route, increase head losses. The extent of head losses is a function of the following variables: a. Pipe length b. Pipe diameter c. Pipe wall smoothness d. Water flow-rate (discharge) e. Water viscosity

10.2.1 Friction Losses As mentioned before, there are two types of friction losses: Major (longitudinal) losses: losses in water flow along straight pipes. Minor (local) losses: are created by the flow at bends and transitions in different accessories. If the flow velocities are high through many bends and transitions in the system, the minor losses can build-up and become substantial losses. 10.2.1.1. Longitudinal Friction Loss es The calculation of friction head losses in pipes is based on the following data: a. The friction coefficient (for convenience - C) of the pipe, which is a constant value for a specific pipe and depends on the smoothness or roughness of the inner surface of the pipe wall. b. The internal pipe diameter d, the greater the diameter, the smaller the friction losses in a given flow-rate. c. Flow-rate Q, the greater the flow-rate, the greater the friction losses. d. Pipe length L, the greater the length, the greater the friction losses. The common equation used to calculate friction losses of water flow along a pipe is known as the Hazen-Williams equation. 92

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Q J( ‰) = 1.131 × 10 12 × ( )1.852 × D −4.87 C

(Eq. 10.1)

Where: J (‰) = head-loss (m. per 1000 m. length) Q = flow-rate (m3/h). C = friction coefficient (indicates inner pipe wall smoothness, the higher the C coefficient, the lower the head losses). D = inner pipe diameter (mm) The Hazen-Williams equation is valid in a narrow range of temperatures and flow patterns. The friction coefficient C that depends on the smoothness of the internal pipe wall may decrease along time, due to corrosion in non-coated steel pipes and accumulation of precipitates in all types of pipes. In small diameter laterals, the Darcy-Weisbach equation gives more accurate results in calculating head losses. Most commonly it takes the following form:  LV 2   (Eq.10.2) Hf = f   D2g  Where: Hf = Head-loss – m. f = Darcy-Weisbach friction factor L = Pipe length – m. V = Flow velocity – m/sec D = Inner pipe diameter – m. g = gravitational acceleration (9.81 m/sec2) Table 10.2. Friction Coefficients C (Hazen-Williams)

Pipe material

f - mm (Darcy-Weisbach)

PVC and PE

0.0015 - 0.007

140-150

Asbestos-cement

0.3

130-140

New steel

0.045 – 0.09

110-120

5 year old steel

0.15 – 4.0

80-90

Steel with internal concrete coating

0.3 – 1.0

110-120

Concrete

0.3 – 5.0

90-100

Both the Hazen-Williams and Darcy-Weisbach equations include a parameter for the smoothness of the internal surface of the pipe wall. In Hazen-Williams, it is the dimension-less C coefficient and with Darcy-Weisbach the roughness factor f, expressed in mm. In Hazen-Williams equation, as the C coefficient is higher, head losses will be lower. On the opposite, in the Darcy-Weisbach equation, higher values of the friction factor f indicate higher head-losses. The head losses can be expressed graphically by the slope of the Piezometric line along the length of the flow path. In the category of friction losses, the Piezometric line declines 93

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gradually and is depicted as a straight, sloping line, descending in the flow direction. An abrupt, vertical decline of the Piezometric line expresses local losses. There are no local losses at all in section (1) - (2) of the pipe shown in Fig. 10.1. The only head loss in this section is the friction loss. This loss is expressed by the incline of the Piezometric line along the section; the value of the loss hf equals the drop of the Fig. 10.1. Graphic Presentation of Friction Head energy line in section (1)-(2). As there are no changes in the values of C, d and Q, the value of the friction loss per a length unit is constant and increases uniformly in the flow direction along the pipe. The friction loss per longitudinal unit (the hydraulic gradient) is commonly expressed by the letter J. Its value is calculated by: (Eq.10.3) From Fig. 10.1., it is explicit that J is indeed the incline of the Piezometric line. It is usually expressed in percentage (%), per-mil (0/oo), or in the form of a decimal fraction. Example: if in Fig. 10.1 L = 100 m . , E1 = 101.5 m . , E2 = 100.0 m , Then:

J is the hydraulic gradient and is absolutely independent of the slope of the pipe! 10.2.1.2. Minor (local) Head-losses Minor head-losses are expressed as an equivalent length factor that adds a virtual length of straight pipe of the accessory diameter to the length of the pipe under calculation. Specific cases of local pressure losses: 10.2.1.2.1. Emitter Connecting Tubes Disturbance to Water Flow in Lateral Some micro-emitters are connected to laterals by means of small diameter tubes with barbed or screwed protrusions. These protrusions disturb water flow in the lateral and induce increased head losses. The rate of disturbance to the flow is designated by the coefficient Kd. The range of Kd is 0 – 2.00 (and sometimes higher). As this value is higher, head-losses increase. The Fig. 10.2. Feeding Micro-tube Connection value of Kd depends on the size and nature of the protrusion and the inner cross section of the lateral.

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10.2.1.1.2. Head Losses in the Connecting Tubes Micro-sprinklers and micro-jets utilize occasionally small diameter micro tubes of 4 – 8 mm inner diameter for connection between the lateral and the emitter. The smaller cross-section may generate considerable head losses in relatively short tubes of 50 – 100 cm. Decrease of pressure below the requested operation pressure may distort the optimal distribution pattern of micro-sprinklers and micro-jets. To prevent excessive head losses, emitters with a flow-rate higher than 30 l/hour will be connected to the lateral with tubes having a minimum inner diameter of 6 mm. 10.2.1.1.3. Head-losses in Valves and Accessories As mentioned before, head losses in accessories are often designated as the losses in equivalent length of a virtual pipe having the same diameter as the accessory. Nomograms of head losses as a function of flow-rate appear in commercial brochures and manuals. Certain producers designate a flow factor to valves and similar accessories. This value indicates the flow-rate that creates head losses of 10 m. (1 bar) while flowing through the accessory. Kv =

Q (∆p )0.5

(Eq. 10.4)

Where: Kv – flow factor, m3/hour flow-rate with head-loss of 1 bar Q – flow-rate, m3/hour ∆p – pressure drop, bars

Fig. 10.3. Head-losses in Hydraulic Valves (example)

Example: Kv = 50; What is the head loss when Q = 30 m3/h Manipulation of Eq. 10.04: ∆p = (Q/Kv)2 ∆p = (30/50)2 = (0.6)2 = 0.36 bar = 3.6 m. 10.2.1.2. Total Dynamic Head (TDH) The total dynamic head that has to be created by the pump is the sum of the pumping suction lift (the difference between water surface height at the source, and pump height), the requested working pressure in the emitters, and friction losses within the irrigation system. The energy consumed per pumped unit of irrigation water depends on the total dynamic head output of the pump and its pumping efficiency. As mentioned above, the total dynamic head depends on: a.

The vertical distance that the water is lifted

b.

The pressure required in the emitters' inlets

c.

The friction losses that are created by the water flow from the water source through the pipelines and accessories such as valves and filters. 95

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As mentioned before, pumping system efficiency depends upon the pump maintenance level, its power unit effectiveness, and the efficiency of power transmission between them. The power input required by the pump is calculated with the formula below: N=

Q ×H 270 × η

(Eq. 10.5)

Where: N = required input - HP Q = pump discharge – m3/h H = total dynamic head – m η = pump efficiency – expressed as a decimal fraction Example: Q = 200m3; H = 150 m; η = 0.75. N = 200 X 150/(270 X 0.75) = 148 HP When measuring pressure, it should be remembered that the pressure gauges are calibrated to read 0 (zero) at atmospheric pressure (about 1 bar). This is important in the operation of devices such as Venturi suction injectors.

10.3. Operating Pressure The operating pressure is the pressure required at the emitters to guarantee effective performance and uniform water distribution. The range of the appropriate operating pressure of the emitter is defined and published by the manufacturer in the operating manual. The type of emitter and its operating pressure have to be taken into account in irrigation system design and irrigation scheduling. The design of the distributing pipelines has to guarantee the appropriate operating pressure in the emitters. The term ‘working pressure’ (PN) refers to the maximal allowed pressure in a component of the irrigation system (pipe, filter, etc.) that will not result in damage to the element by excessive pressure. There are different procedures for calculation of head losses. In the past, slide rulers and nomograms were routinely used. Nowadays, most system designers use dedicated software and on-line calculators. Head-losses in distributing pipes with multiple outlets differ from head-losses in nondistributing pipes. When using m. (meters) as head units, head-loss values are expressed in % or ‰ of pipe length. The actual head-losses are obtained by multiplying the percentage/ per-mil value by the pipe length (in m. units). Christiansen friction factor (F) is used to calculate the head losses in pipes with multiple outlets such as distributing mains and sub-mains, manifolds and laterals. This factor accounts for the decrease in flow along the lateral and depends upon the number of outlets (N) and the exponent (m = 1.76) of the flow-rate (Q) in HazenWilliams equation. The formula for calculating this factor is as follows: F = 1/(m+1) + 1/(2N) +((m-1)0.5/(6N)2)

(Eq. 10.6)

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For a lateral with more than 10 emitters, F ≈ 0.40 can be used regardless of the friction loss formula utilized. The head-loss due to friction in laterals is then determined by:

Table 10.3. Multiple Outlets Factor F Number. of outlets

F

Where:

1

1.00

Hf is the head-loss due to friction in the lateral.

5

0.410

Hp is the head-loss due to friction of the same flow-rate in a nondistributing pipe of the same diameter and length.

10

0.384

Hf = F× ×Hp

(Eq. 10.7)

20 0.373 As mentioned before, in laterals where connecting tubes are 0.368 inserted, molded inside or nailed with the stem protruding into 40 the inner cavity of the lateral, the protrusions disturb the water 100 0.366 flow and increase the head losses. These additional head losses are designated by Kd – the disturbance coefficient. The values range from zero to 2.0 and higher. When these values are high, the disturbance to flow and the derived head losses are substantial and commits a shorter lateral length.

10.4. Hydraulic Characteristics of Emitters Pressure variations have a different effect on the flow-rate of various emitter types. The impact depends on design and construction. The relationship between the operating pressure and the flow-rate of the emitter is calculated via the following equation: Q = k× × Px

(Eq. 10.8)

Where: Q = emitter flow-rate – l/h k = emitter discharge coefficient – depends on the configuration of the water path in the emitter and the units of pressure and flow-rate. P = Pressure at the emitter's inlet – m. x = emitter discharge exponent The emitter exponent indicates the relationships between the pressure and the flow-rate of the emitter. The range of emitter exponents is 0 – 1. in most sprinklers the exponent is around 0.5.

Table 10.4. Effect of the Emitter Discharge Exponent on Pressure – Flow-rate Relationship Exponent

0.4

Pressure change - % 10 20 30 40 50

Flow-rate change - % 3.9 7.6 11.1 14.4 17.6

0.5

4.8 9.5 14.0 18.3 22.5

0.6

5.9 11.6 17.1 22.3 27.5

0.7

0.8

6.9 13.6 20.2 26.6 32.8

7.9 15.7 23.3 30.9 38.3

The larger the emitter exponent, the more sensitive is the flow-rate to pressure variations. A value of 1 means that for each percentage change in pressure there is an identical percentage change in flow-rate. An exponent value of 0 (zero) means that the emitter's flow-rate is not affected by pressure changes. That happens in compensating emitters above the regulating pressure threshold.

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10.5. Calculation of Head Losses As mentioned before, slide rulers, tables, nomograms, hand-held and on-line calculators as well as dedicated software can be used to calculate head losses. Manufacturers publish tables and nomograms showing the head losses in their products. Valve producers use the Kv Flow Factor that designates the discharge of the valve in m3/h units at 10 m (1 bar) head loss.

10.6. Technical Data Sprinkler and micro-emitters manufacturers provide detailed technical data in catalogs or on-line, about the flow-rate - pressure relationships of their products. These data should be used for determining lateral length and the pressure required at the lateral inlet. In taking decisions, the convention of maximum allowed flow-rate difference below 10% between emitters in a simultaneously irrigated area has to be followed. Manufacturers provide tables indicating the acceptable lateral length in a plateau and selected slopes for a given emitter and lateral combination that keeps the head differences in the allowed range of ± 5% around the average flow-rate.

10.6.1. Pressure Measurement An adequate pressure regime in the irrigated area is a prerequisite for optimal irrigation. Each type of emitter has its allowed pressure range in which the water distribution is satisfactory. Deviation from the allowed range decreases the efficiency of water application. The pressure can be measured at fixed measuring points by mounted pressure gauges or by portable pressure gauges that are fitted to measure the pressure in the sprinkler nozzle. Another device is a portable pressure gauge, equipped with a needle that can be inserted into specific nipples that have been installed on specific accessories in the irrigation system like elbows, plugs, fertigation devices, etc.

10.6.2. Calculation of Longitudinal Head Losses

Fig. 10.4. Pressure Measurement

The calculation of the predicted head losses is essential in the design of a new irrigation system. It is particularly important in the comparison of the actual performance of the irrigation system with the designed performance. The discharge of the emitter is related to the pressure according to the formula: (Eq. 10.9) When: Q = Emitter discharge, m3/h P = Sprinkler pressure, bar. d = Nozzle nominal diameter, mm C = Coefficient dependent on the sprinkler structure. Its average value is 0.9.

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Table 10.5. Head-losses in Non-distributing Aluminum Pipes, m. Head per 100 m. of Pipe Length (without Outlets) Discharge M 3/h 2 3 4 6 8 10 15 20 30 35 40 45 50 55 60 80 90 100 120 150 180 200 250 300 350 400 425 450

2”

Nominal Diameter 4” 6”

3” 0.32 0.71 1.24 1.89 3.54 5.69 13.32 20.95 49.50 63.00

0.02 0.09 0.16 0.23 0.44 0.72 1.66 2.62 6.07 7.82 9.70 11.71 14.39 17.02 21.18 34.50 44.60

0.01 0.03 0.05 0.09 0.17 0.39 0.63 1.40 1.82 2.28 2.78 3.36 3.94 4.90 8.05 10.42 12.90 19.31 29.90

0.03 0.07 0.19 0.23 0.30 0.37 0.44 0.51 0.60 1.06 1.36 1.68 2.58 3.89 5.02 6.23 9.18 14.60 18.90

8”

0.01 0.04 0.05 0.06 0.08 0.10 0.12 0.15 0.26 0.33 0.40 0.58 0.92 1.20 1.50 2.19 3.48 4.51 5.11 6.14 6.85

The calculation of head-losses can be done with the Hazen-Williams formula. In daily life, tables, nomograms, specific slide-rules and computer software facilitate the determination of head losses. Example: L = 500 m., Q = 60 m3/h, d = 6” It is found in the table above that at flow-rate of 60 m3/h in 6” aluminum pipe, the head-loss is 0.6 m. per 100 m. length (0.6%). The head-loss in 500 m. length will be 0.6 X 500/100 = 3 m. 10.6.2.1. Head-losses in Laterals The results obtained from the tables and the nomograms relate to a blind pipe without outlets. Discharge of water from outlets along the pipe decreases the accumulating total head loss in the pipe, compared with a non-distributing pipe. In this case the calculation of the head losses along the pipe can be done incrementally between the outlets. 99

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A shortened procedure facilitates the calculation of the head losses in laterals by the multiplication of the head loss in blind pipes by the F coefficient. As mentioned before, the value of the F coefficient depends upon the number of outlets along the pipe and the distance of the first emitter from the entrance to the lateral. This procedure is valid if the discharge of each emitter and the intervals between the emitters along the lateral are equal. In table No. 10.6, (a more detailed version of table 10.3). the F coefficient in laterals is presented. X=1 indicates that the distance between the sub-main/manifold and the first emitter is equal to the intervals between the emitters along the lateral. X=1/2, indicates that the distance between the sub-main and the first emitter is half of the distance that exists between the emitters along the lateral. Example: L = 114 m. distance from the sub-main to the first sprinkler 6 m. Intervals between sprinklers – 12 m. d = 2”, Sprinkler discharge – 1.5 m3/h. What will be the head-loss in the lateral? The number of sprinklers along the lateral is 10. 114m. – 6m. of the initial section = 108m. 108m./12m. (The interval between the sprinklers) = 9 segments = 10 sprinklers. The total nominal discharge of the lateral: 1.5 m3/h X 10 = 15 m3/h. The head-loss in non-distributing 2” lateral will be (from table 10.5): For 100 m. length 13.32 m. For 114 m . length: 1 3 . 3 2 m . X 114/100 =1 5 . 1 8 m. From table No. 10.6. The F coefficient for 10 emitters (third columns X=1/2) = 0.353. The actual head loss is: 1 5 . 1 8 m . X 0.353 = 5.36m. The F coefficient range is from 0.5 for two outlets to 0.33 for more than 100 outlets.

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Table 10.6. F Coefficient in Laterals Number of X=1 X = 1/2 Emitters 1 1.0 1.0 2 0.625 0.500 3 0.518 0.422 4 0.469 0.393 5 0.440 0.378 6 0.421 0.369 7 0.408 0.363 8 0.398 0.358 9 0.391 0.355 10 0.385 0.353 11 0.380 0.351 12 0.378 0.349 13 0.373 0.348 14 0.370 0.347 15 0.367 0.346 16 0.365 0.345 17 0.363 0.344 18 0.361 0.343 19 0.360 0.343 20 0.359 0.342 22 0.357 0.341 24 0.355 0.341 26 0.353 0.340 28 0.351 0.340 30 0.350 0.339 40 0.345 0.338 50 0.343. 0.337 100 0.338 0.337 >100 0.333 0.335

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10.6.2.2. Pressure and Topography The topography in the field affects the pressure in the irrigation system. Elevation of 1 m. in topographic height decreases the pressure by 1 m. (0.1 atm.). Downward decline of 1 m. increases the pressure by 1 m. The slope along the pipe can be expressed in %. That facilitates the calculation of the combined effect of friction in pipes and topography in each point in the field. 10.6.2.3. Nomograms and Slide-rulers In daily use, the common practice of head-loss determination is accomplished by the use of nomograms, slide-rulers and computers.

Fig. 10.5. Slide-ruler for Head-loss Calculation in Pipes 10.6.2.4. Head Losses in PVC and PE Pipes The calculation of head losses in PVC and polyethylene pipes is similar to that of aluminum pipes. Since the plastic pipes are designated by their nominal external diameter, it is necessary to know the wall thickness. Knowing the external diameter and wall thickness facilitates the calculation of the internal diameter and the net crosssection of the pipes. These values are required for the calculation of head losses according to the Hazen-Williams formula and for the use of the common head-loss nomograms, in which the internal diameter is the related parameter. As mentioned before, in plastic pipes, as the nominal working pressure is higher, the wall thickness has to be greater and hence the internal diameter and the free crosssection will be smaller. For example, in PE pipes of 50 m m . of 4, 6 and 8 bars. working pressure classes, the greatest internal diameter is in the grade 4 pipe and the smallest is in the grade 8 pipe. For the same flow-rate, the higher head-losses will occur in the 8-grade pipe and the lower in the 4-grade pipe. Two distinct nomograms are given on page 104 for the most prevalent PE pipe diameters of rigid (high density) and soft (low-density) PE pipes. Calculation example: (using the Hazen-Williams nomogram) The head -loss of a 3" aluminum sprinkler lateral with 16 sprinklers, positioned 12 m apart, has to be calculated. The nominal (average) sprinkler flow-rate (discharge) is 1.5 m3/h; the length of the lateral is 186 m. The friction coefficient [C] of the pipeline is 120.

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Solution: The cumulative discharge of 16 sprinklers with an average discharge of 1.5 m3/h per sprinkler is 24 m3/h. A line is drawn in the "Nomogram for The Determination of the Hydraulic Gradient in Pipes" (to the right), from the point A of 24 m3/h on the flow-rate (Q) scale, through the point indicating the pipeline diameter (D) = 3" on the diameter scale. The drawn line meets the axis of the nomogram in point B. Second line is drawn from the point C that indicates 120 on the C coefficient scale through the crossing point B, which is already marked on the nomogram axis. The line is stretched to the J (head-loss) scale. The point D on the J scale indicates head-loss of 43‰, namely 43 m. per 1000-m length of the pipe. For a 186 m long whole pipeline the head loss is 43 x 186/1000 | 8 m. But the sprinkler lateral is a distributing pipeline. We have to multiply 8 by the F coefficient. The first sprinkler is mounted on the end of the first aluminum 6 m. long pipe, the distance from the sub-main to this sprinkler is a half of the distance between the sprinklers along the lateral that is 12 m. From Table 10.6. F Coefficient in laterals, in the X=1/2 column, it is found that F coefficient for 16 outlets on the lateral is 0.345. Multiplication of this figure (0.345) by 8 m. (the head-loss in 186 m. of non-distributing lateral, depicted from the nomogram) indicates head-loss of 2.76 m. in the lateral. 8 x 0.345 = 2.76

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Fig. 10.6. Nomogram for Hazen-Williams Formula

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Fig. 10.7. Nomograms for Head-loss Determination In Polyethylene Pipes

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Fig. 10.8. Nomogram for Local Hydraulic Gradient Determination in Accessories

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Fig. 10.9. Nomogram for Calculation of Head-losses in LDPE Pipes. Class Designation Relates to the Working-pressure (PN) in bar. 1 bar = 10 m Adapted from "Plassim" brochure

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Fig. 10.10. Nomogram for Calculation of Head-losses in HDPE Pipes. The Class Designation Relates to the Working-pressure (PN) in bar. 1 bar = 10 m. Adapted from "plassim" brochure

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Fig. 10.11. Nomogram for Calculation of Head-losses in PVC Pipes. The Class Designation Relates to the Working-pressure (PN) in bar. 1 bar = 10 m. Adapted from "Plastro" brochure

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11. WATER MOVEMRNT AND DISTRIBUTION IN THE SOIL 11.1 Introduction The soil has two fundamental functions in growing plants. a. The substrate in which the plant is anchored by means of its root system. b. A source of water and nutrients. Optimized irrigation has to provide water in equal amounts to each of the plants in the irrigated area. Two patterns of water spread on soil surface with pressurized irrigation technologies are recognized. a. Uniform coverage of the irrigated soil surface. b. Localized wetting of the soil surface in such a way that each plant receives equal amount of water. The first pattern is implemented in sprinkler irrigation of field crops, some types of vegetables and overhead irrigation in orchards. The second pattern is common in under-canopy irrigation in orchards and in drip irrigation in all the crops. In order to optimize the irrigation design and management, certain soil properties have to be carefully taken into account.

11.2. Soil Properties 11.2.1. Soil Texture Accurate water application has to be adjusted to soil properties. The soil is created by decaying of rocks into tiny soil particles. The soil preserves its crumbled shape and porosity, with particles that vary in size and are classified according to international conventions. Table 11.1. Soil Classification According to Particle Diameter Fraction

Diameter in mm.

Clay