BS 7562-5 Irrigation
Short Description
BS 7562-5...
Description
BS 7562-5: 1993
BRITISH STANDARD
Planning, design and installation of irrigation schemes — Part 5: Guide for irrigation equipment
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BS 7562 7562-5: -5:19 1993 93
Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Agricultural Machinery and Implements Standards Policy Committee (AGE/-) to Technical Committee AGE/30, upon which the following bodies were represented: Agricultural Engineers’ Association British Agricultural and Garden Machinery Association Ltd. Health and Safety Executive Ministry of Agriculture, Fisheries and Food National Farmers’ Union Silsoe College Silsoe Research institute UK Irrigation Association National Rivers Authority Well Drillers’ Association
This British Standard, having been prepared under the direction of the Agricultural Machinery and Implements Standards Policy Committee, was published under the authority of the Standards Board and comes into effect on 15 November 1993 © BSI 07-1999
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Amendments issued since publication Amd. No.
Date
Comments
The following BSI references relate to the work on this standard: Committee reference AGE/30 Draft for comment 88/72250 DC
ISBN 0 580 22447 3
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BS 7562 7562-5: -5:19 1993 93
Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Agricultural Machinery and Implements Standards Policy Committee (AGE/-) to Technical Committee AGE/30, upon which the following bodies were represented: Agricultural Engineers’ Association British Agricultural and Garden Machinery Association Ltd. Health and Safety Executive Ministry of Agriculture, Fisheries and Food National Farmers’ Union Silsoe College Silsoe Research institute UK Irrigation Association National Rivers Authority Well Drillers’ Association
This British Standard, having been prepared under the direction of the Agricultural Machinery and Implements Standards Policy Committee, was published under the authority of the Standards Board and comes into effect on 15 November 1993 © BSI 07-1999
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Amendments issued since publication Amd. No.
Date
Comments
The following BSI references relate to the work on this standard: Committee reference AGE/30 Draft for comment 88/72250 DC
ISBN 0 580 22447 3
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Contents
Committees responsible Foreword 1 2 3 4 5 6 7 8 9 10 11 12
Page Inside front cover ii
Scope Informative references Definitions Sprinkle in-field equipment Trickle/bubbler in-field equipment Pipes and fittings Suction and delivery pipework Valves Flow meters Pump installations Applying chemicals Safety
1 1 1 1 7 9 14 15 18 18 24 24
Table 1 — A classification of irrigation systems used in the UK List of references
Inside back cover
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BS 7562-5:1993
Foreword This Part of BS 7562 has been prepared under the direction of the Agricultural Machinery and Implements Standards Policy Committee and contains recommendations on good practice in the planning, design and installation of irrigation schemes in the UK, together with information and guidance. It is intended for the use of engineers and farmers having some knowledge of the subject. It embodies the experience of engineers successfully engaged on the design and construction of irrigation schemes so that other reasonably qualified engineers may use it as a basis for the design of similar irrigation schemes. This Part of BS 7562 contains information and represents good practice at the time it was written and, inevitably, technical developments may render parts of it obsolescent in time. It is the responsibility of engineers concerned with the design and construction of schemes to remain conversant with developments which have taken place since publication. This standard has been prepared in six Parts as follows. — Part 1: Glossary of terms; — Part 2: Guide for acquisition of site data; — Part 3: Irrigation water requirements1); — Part 4: Guide to water resources; — Part 5: Guide for irrigation equipment; — Part 6: Guide for feasibility and implementation procedures. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations.
Summary of pages This document comprises a front cover, an inside front cover, pages i an d ii, pages 1 to 26, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. 1) In
preparation. --``,,```,,,``,```,``,``````,``,-`-`,,`,,`,`,,`---
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1 Scope This Part of BS 7562 gives guidance on the equipment required for irrigation schemes. It deals specifically with sprinkler and trickle/bubbler irrigation as the most common methods of irrigation in the UK and covers in-field irrigation equipment, pipelines, pump installations, and pump suction and delivery pipework.
2 Informative references This Part of BS 7562 refers to other publications that provide information or guidance. Editions of these publications current at the time of issue of this standard are listed on the inside back cover, but reference should be made to the latest editions.
3 Definitions For the purposes of this Part of BS 7562 the definitions given in BS 7562-1:1992 apply.
4 Sprinkle in-field equipment 4.1 Introduction This is the equipment which is laid out, temporarily or permanently, in the field being irrigated. A wide range of in-field equipment is available but that commonly used in the UK is described in this British Standard. A classification is provided in Table 1. The selection of appropriate in-field irrigation equipment is based on many factors including capital cost, operating cost, labour requirements and suitability for the farm. 4.2 Water application devices 4.2.1 General The function of water application devices is to apply water as uniformly as possible to the crop and soil. The most common application devices used to apply water are rotary impact sprinklers, guns and fixed spray heads. 4.2.2 Rotary impact sprinklers
Sprinklers should be operated within the manufacturers’ specified range of pressures for uniform water application. Sprinkler operation with too high a pressure will cause excessive break up of the water jet, loss of wetted radius and excess water applied near the sprinkler head. Low operating pressure at the sprinkler will result in inadequate break up of the jet, large droplets and uneven application of water. The size of the nozzle(s) determines the sprinkler discharge and the wetted diameter. Nozzle diameters range from 2 mm to 3 mm up to 50 mm. Sprinklers may have one or two nozzles. Common trajectory angles for sprinklers are 24° and 30° measured from the horizontal. Such sprinklers are used on a wide variety of irrigation systems, including hand move and mechanical move equipment. Low angle sprinklers, having trajectory angles ranging from 0° up to about 15° produce a profile which is less subject to distortion by wind but may not be as uniform in application. Typical applications for low angle sprinklers include under tree orchard irrigation and centre pivots operating in windy conditions. The average application rate from the sprinklers (in millimetres per hour) should not exceed the basic infiltration rate (in millimetres per hour) of the soil. This ensures that water infiltrates into the soil thus avoiding the problem of surface water run-off. The uniformity of water application is described by Christiansen’s coefficient of uniformity. Details of the coefficient and its measurement are provided in BS 7459-2. The choice of the most appropriate uniformity coefficient depends largely on the crop being irrigated. The spacing between sprinklers should be as recommended by the manufacturer and shown in performance tables. The wetted patterns from sprinklers should overlap to achieve an appropriate coefficient of uniformity. The degree of overlap will vary according to the water application pattern and the wind conditions.
Rotary impact sprinklers are the devices most in use for spraying water. Sprinklers of varying sizes may be used on a wide range of irrigation systems including conventional and mobile lateral systems, see Table 1. The design and performance requirements for rotary impact sprinklers are described in BS 7459-1 and BS 7459-2.
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BS 7562-5:1993
Table 1 — A classification of sprinkle irrigation systems used in the UK Systems
Conventional systems
Water application devices
— portable — hand move — roll move — tow line — semi-permanent
Mainly use small rotary impact sprinkers, but guns, fixed sprays and bubblers are also used
— sprinkler hop — pipe grid — hose pull
— permanent Mobile gun systems
— hose drag — hose pull
Mainly guns, but in some cases the gun is replaced with a boom device with small rotary impact sprinklers or fixed sprays
Mobile lateral systems
— centre pivot — linear move
Small rotary impact sprinklers or fixed sprays
Spray lines
— stationary — oscillating — rotating
Fixed sprays
Wind will distort the wetting patterns of sprinklers. The amount of distortion depends upon the wind speed and the size of the water droplets. The greater the wind speed and the smaller the water droplets the more distortion will occur. Wind distortion can be counteracted by spacing the sprinklers closer together but care should be taken as this may also increase the application rate. If the application rate exceeds the infiltration rate of the soil, run-off may occur. The direction of the wind may be an additional problem especially if the wind direction changes during the irrigation set. In this situation the best results may be obtained by ignoring the effects of wind altogether and operating the sprinklers on their recommended spacings for low wind speeds. 4.2.3 Guns Guns are large rotary sprinklers which have a large wetted diameter. They are commonly used in mobile systems in the UK but they can also be used in conventional systems. Guns may be used on various irrigation systems either fixed or mobile. They normally have discharges from 10 m3/h up to and above 125 m3/h and operate at pressures from 2.0 bar2) up to and above 8.0 bar. The selection of the operating pressure depends upon nozzle size and type and droplet size required.
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Water droplet sizes from guns may be unacceptably large for certain soil types and crops, causing damage to both soil and crop. Careful selection of nozzle diameter and type and operating pressure should be made to ensure that the resultant droplets are suitable for the soil and the crop. Gun nozzle diameters can vary from 12 mm up to and above 40 mm. Two main types of nozzle are available; ring nozzles and taper nozzles. Ring nozzles are designed to produce acceptable droplet sizes at lower operating pressures. Taper nozzles are designed to produce the maximum wetted throw but droplet sizes are increased. The throw is not only affected by the operating pressure and nozzle diameter and type but also by the construction of the gun. The length of the range tube and its diameter, plus the use of straightening vanes inside the range tube, combine to affect the maximum throw. The application rate tends to be greater than for the small rotary impact sprinklers. The recommended spacing depends upon the wetted diameter, wind speed and direction and the required coefficient of uniformity. Gun spacing recommendations vary according to whether the gun is working on a grid system, a mobile unit or is used on a centre pivot or linear move.
1 bar = 105 N/m2 = 105 Pa.
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BS 7562-5:1993
Guns may be used for full or part circle irrigation. Full circle irrigation would usually be applicable to fixed grid irrigation systems. Mobile gun systems usually use part circle applications of 270° to 300° arc. Guns may also be used on the end of centre pivots and linear move machines to irrigate an arc of 180° or less. There are two main types of drive systems used for rotating the gun. Impact drives operate using the water flow that leaves the nozzle moving an impact arm up and down or sideways causing the gun to rotate. Gear drives operate by passing a small quantity of the main supply through or over a turbine gear drive assembly. This causes the gun itself to rotate via a gear mechanism. The drive mechanism may be affected by water quality. Care should be taken with gear drive systems to ensure that grit or other particles do not cause the drive system to fail. Filtration equipment may be required for some systems. Guns normally operate with trajectory angles between 18° and 25°. Low angle guns may be used on applications where wind affects the gun performance, but the wetted diameter of the gun is reduced. Adjustable trajectory guns may be suitable for certain situations such as operating in high wind conditions where reduced wind drift is required. The part circle mechanism fitted to guns should provide adequate adjustment to cover the range of arcs required. Usually the range is between 45° and 330°. When returning to the start position, the reverse action of impact driven guns may occur at high speed. In this case the riser assembly should be strong enough to resist the forces. Operator safety should be considered where there is a risk that a gun may hit the operator when fast reversing. Slow reverse action sectoring devices are often now used on guns and these produce less strain on the connection assemblies.
The thrust forces resulting from gun operation may be high due to the flows and pressures used and the construction of the riser is critical for correct gun performance. The riser strength should be sufficient with its support to prevent flexing of the riser which may cause either failure or poor gun performance. Risers used on grid systems should be designed with adequate support structures to ensure that when the gun is operating the riser is sufficiently stable. The riser should be of suitable diameter to ensure that the velocity of water through it is not excessive causing high turbulence which may affect the performance from the gun. Risers fitted to the trolley units used on self travellers should be sufficiently strong to resist breakage. The trolley base should be so designed that there is no risk of tipping over when operating under normal irrigation conditions. 4.2.4 Fixed spray heads Fixed spray heads may be used to apply water either to the total ground area or to a specific area around a plant. Spray jets may be used on conventional irrigation systems, such as under tree irrigation and also on centre pivots and linear move machines. 4.3 Sprinkle irrigation systems NOTE The irrigation systems most commonly used in the UK are listed and classified in Table 1.
4.3.1 Conventional systems 4.3.1.1 General Conventional systems are the most common type of system in use and comprise pipes, small rotary impact sprinklers and risers which are moved, often by hand, around the field to complete an irrigation. A characteristic of this type of system is that the pipes and sprinklers are stationary during irrigation and then moved between irrigations.
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BS 7562-5:1993
4.3.1.2 Portable The most basic and simplest system is the portable hand-move system. The pipes and sprinklers are all portable and moved by hand for each irrigation. As this tends to be very labour intensive, several developments have been made to this system to reduce the labour input. If the field layout allows, the laterals which carry the sprinklers should be laid along the contours to ensure as little pressure variation as possible caused by difference in height. The lateral may be operated down the slope provided that the maximum pressure variation along the lateral does not exceed 20 % of the sprinkler’s recommended operating pressure. If the slope would cause a greater pressure variation, then pressure regulators should be fitted to the sprinklers to produce correct operation. A pressure regulator may be fitted under the sprinkler inlet connection or a pressure regulating/flow controlling nozzle may be inserted at the nozzle. Sprinkler laterals may be laid out up the slope where this is the only possible layout. Pressure regulating or flow regulating devices should be fitted to the sprinkler where the pressure variation along the lateral is greater than 20 % of the sprinkler’s recommended operating pressure. Ideally, sprinkler laterals should be laid out at right angles to the prevailing wind for a more u niform irrigation. This should take preference over layout in relation to contours. The number of irrigation sets per day depends on the depth of water to be applied at the rate per hour and the time it takes to move the sprinkler laterals. The fewer the number of irrigation sets per day and the longer the number of hours per set the greater will be the total possible operating hours per day. The application rate (in millimetres per hour) relates to the application heads applying water on a unit area operating on a grid system, either square, rectangular or triangular The application rate per hour calculated here is used to estimate the total depth applied during the irrigation set. Several factors affect the sprinkler spacing, both along the lateral and between laterals. These include wind speed, coefficient of uniformity, application rate, the crop and the soil. Sprinkler spacing should be reduced according to wind speed. The lateral pipe diameter is chosen so that the pressure loss along the lateral is less than 20 % of the recommended operating pressure of the sprinkler. In this way the changes in pressure will not seriously affect sprinkler performance and uniformity.
Normally sprinkler laterals should not exceed 100 mm in diameter as bigger pipes are much heavier and are more difficult to move around the field. Pipe lengths usually used for sprinkler laterals are either 6 m or 9 m. Pipes that are 6 m are lighter in weight, are easier to connect and disconnect and are preferred, especially if large diameter laterals a re used. Sprinkler risers should be of sufficient height to allow the sprinkler to irrigate over the top of the crop and should be adequately supported to avoid bending and vibration as the sprinkler rotates. Both aluminium and steel lightweight galvanized steel pipes may be subject to corrosion if fertilizers or other chemicals are applied through the irrigation system. The manufacturer of the pipe and fittings should be consulted if this practice is considered. The ease of connection and disconnection of coupling lateral pipes should be considered carefully when selecting the type to be used. Couplings that can be operated by one person may be favoured where labour is short. Sprinkler risers may have either permanent or quick coupling connections to the sprinkler lateral. The type of riser used depends upon the method of operation of the system, the riser height and the stability required. The following briefly describes types of portable hand-move systems. a) Roll-move system The roll-move system comprises a sprinkler lateral mounted on wheel assemblies so that the lateral forms the axle for the wheels. The sprinkler lateral is stationary while irrigating. The water supply to the lateral is closed off when it is moved. A power unit provides the power source for driving the wheels. It is preferable that the system is operated in level fields to alleviate potential problems that may be caused by uneven ground. If used on sloping ground, the system should be aligned with the lateral at right angles to the land contours. If it is operated running parallel to the contours there is a risk that the unit may run down the slope while the system is operating. Brake equipment may be fitted to the wheel assembly to prevent this happening. A balance weight self-levelling device is included in the connection for each of the sprinklers to ensure that the sprinkler operates in the vertical position when irrigating.
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BS 7562-5:1993
b) Towline system
4.3.1.4.4 Hose-pull system
The towline irrigation system uses equipment similar to that used for the conventional hand move portable system. The lateral pipe is mounted on wheeled bases so that it can be towed from one irrigation set position to another. Special fittings are required for the base of the sprinkler pipe and also to support the pipe couplings.
A hose-pull system comprises a sprinkler complete with a stand and support assembly connected to the lateral by a flexible hose. The assembly can operate in several different positions from one connection point working on a grid layout.
Usual diameters on towline sprinkler laterals are 75 mm and 100 mm. Larger diameter pipe may be heavy to pull and therefore more difficult to move. Smaller diameter pipe may not have the strength suitable for the pulling operation.
Mobile systems are distinct from conventional systems because they are moving when applying irrigation water rather than being stationary. This usually improves application uniformity. It also greatly reduces the labour required for irrigation.
4.3.1.3 Permanent systems When sufficient laterals and sprinklers are provided to cover the whole irrigated area so that no equipment needs to be moved during the irrigation season the system is called a solid-set system. The pipes are laid out at the beginning of the season and collected at the end. When the pipes and sprinklers are left in place from season to season the same system is generally referred to as permanent. It is usually used on permanent crops such as orchards. 4.3.1.4 Semi-permanent systems 4.3.1.4.1 General This range of systems has some equipment which is permanently fixed whilst other equipment is moved around the field. Generally this increases the capital cost of the system but greatly reduces the labour required for operations. 4.3.1.4.2 Hop systems A hop system combines the basic characteristics of the portable hand move system with the ability to move the sprinklers to alternative positions along the lateral. This reduces the number of times that the laterals are moved. It may be possible to operate for a greater number of hours per day using this system. The application rate is calculated for a single sprinkler head application as there is no immediate overlap between the sprinklers. Application rates are therefore suitable for a wide range of soils and crops.
4.3.2 Mobile gun systems 4.3.2.1 General
Mobile gun systems use a large single gun type sprinkler to apply water. 4.3.2.2 Hose-pull system This system uses a hard hose which is wound onto a large diameter drum and a gun sprinkler mounted on a trolley. The equipment is operated by towing out the gun and trolley to the furthest position for irrigation in the field. The system is started up and as the gun and trolley irrigate, the hose drum rotates slowly to wind in the hose and the gun. For subsequent set positions the hose drum may simply be rotated or may be moved to another hydrant point position. 4.3.2.3 Hose-drag system
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The hose-drag system comprises a gun mounted on a chassis with a cable drum winding mechanism, a length of winding in cable and anchor and a length of flexible lay-flat hose. The irrigation system operates by positioning the chassis, complete with gun, at the end of the field. The tow cable is pulled out to the other end of the field and anchored. The flexible hose is connected to the chassis and to the water supply valve point. As the gun irrigates, the cable drum gradually winds in, pulling itself along the cable and at the same time dragging the lay-flat hose behind it. If a central water supply valve is used for the supply of water, the irrigation unit can cover twice the area as it is able to irrigate both sides of the valve point. For example, if the machine uses 200 m of hose then it is possible to cover a 400 m wetted strip per irrigation set. 4.3.3 Mobile lateral systems
4.3.1.4.3 Pipe grid systems
4.3.3.1 General
A pipe grid system consists of a complete field layout of pipes, made of either aluminium or lightweight galvanized steel. The pipes, usually 25 mm diameter, are normally laid down at the beginning of the season. Only the sprinklers are moved to complete the irrigation cycles.
Many new irrigation systems have been developed in recent years to try and combine the advantages of conventional sprinkler systems with the mobility of rainguns. These are called mobile lateral systems because they use laterals which move continuously while irrigating.
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BS 7562-5:1993
4.3.3.2 Centre pivot systems
4.3.4 Spraylines
This comprises a lateral pipe supported by a series of towers on wheel drive assemblies. The lateral rotates slowly around a central point irrigating a circular area.
4.3.4.1 General
Centre pivots can usually irrigate large areas up to 100 ha with one machine and can be highly automated. The maximum length of lateral depends on the construction features of the centre pivot and the configuration of the pipe spans. Pivots with 125 mm diameters usually have a limitation of up to 400 m length. Although normally the most economic centre pivot unit is one that rotates in a circle it is also possible to irrigate part circles and to have corner systems and end gun units connected and to the centre pivot. End guns add additional capacity to the machine so that it can irrigate into corners of rectangular fields and awkward field shapes. Due to normally high coefficient of uniformity from a centre pivot irrigation system, it may be practicable to apply chemicals and fertilizers through the irrigation system. ` ` , , ` ` ` , , , ` ` , ` ` ` , ` ` , ` ` ` ` ` ` , ` ` , ` ` , , ` , , ` , ` , , ` -
Sprayline irrigation equipment uses fixed spray heads and may be fixed upon supports above ground level. It can either be static, oscillate from side to side or rotate while irrigating. 4.3.4.2 Fixed/oscillating system The area irrigated by sprayline equipment is usually small in comparison with other types of irrigation system. Small diameter fixed spray nozzles are installed on the lateral and so it may be necessary to use a filter at the water source to avoid blockage. Spraylines apply water at low application rates. Variation of application rate can only be achieved by using different size nozzles or a change of pressure, but the range of nozzle sizes is limited. The sprayline operates at relatively low pressure and therefore pressure regulating or pressure compensating facilities are not normally used. Thus fields should be as level as possible along the run of the sprayline lateral pipe to avoid excessive pressure variation.
Application head accessories include drop arms, drop pipes and booms. Drop arms may be used in conjunction with spray nozzles to allow the water to be applied near the soil surface and to the top of the crop. The effects of windrift and evaporation may be reduced by this procedure.
Sprayline equipment usually uses piping with a diameter of either 25 mm, 32 mm or 50 mm. Due to the small diameter of the sprayline, flow rates that can be achieved per sprayline are relatively low.
Booms may be connected to the centre pivot pipe spans to enable water to be applied at low pressure as a fine even spray pattern using spray heads. The use of a boom allows the application of water over a wider area and should reduce the instantaneous application rate and improve the infiltration rate into the soil.
Wind may adversely affect performance due to the small spray droplets discharged from the nozzles. To counteract some of the effects of wind on the spray it may be possible to offset the nozzles and/or the oscillating mechanism so that better irrigation is achieved.
4.3.3.3 Linear-move system The linear move irrigation system comprises irrigation equipment which is designed to irrigate a square or rectangular area whilst moving slowly across the field. System components are similar in construction to the centre pivot using tower spans, and lateral pipes connected to the tower spans. Water is either fed to the centre of the machine or supplied to one end, being taken from either an open ditch or canal or from water supply points or hydrants on a pressurized main. A central power unit, which may comprise a pump unit on an open water supply system, uses a generator unit to provide the electrical power for operating the linear move.
The sprayline is usually supported above the crop either on short or tall trestles or spikes.
The irrigated area per set depends upon the length of the sprayline lateral and the width between the subsequent sprayline operating positions. A typical area of 0.1 ha per irrigation set is approximately the maximum possible from this type of irrigation equipment per sprayline lateral. 4.3.4.3 Rotating spraylines A rotating sprayline comprises an irrigator unit fitted with booms which rotate by the water pressure from the jets fitted to the booms. The unit is stationary during irrigation. At the end of the set the system is closed down and the unit moved to its subsequent position.
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BS 7562-5:1993
5 Trickle/bubbler in-field equipment 5.1 Introduction Trickle/bubbler irrigation uses emitters or bubblers to apply water locally to individual plants. The systems operate at low pressure and equipment is usually laid out over the complete area to be irrigated and may irrigate either the complete ground area or a percentage of the total ground area depending on the location of emitters. Trickle irrigation is sometimes referred to as drip irrigation. 5.2 Water application devices 5.2.1 Emitters The function of emitters (sometimes called drippers) is to apply water to the roots of the plant. They are described in detail in ISO 9260. The operating flow range for an emitter is usually 2 l/h to 12 l/h. The discharge selected depends upon the crop irrigation requirements, the plant spacing and the soil type. The usual range of emitter operating pressure is between 0.5 bar to 1 bar. Some devices operate over a wider range, up to 2 bar, especially those devices which are pressure compensating. The sensitivity of emitters to clogging plays an important part in their correct performance. The manufacturer should recommend the maximum particle size filtration requirement for emitters to operate correctly. The susceptibility of emitters to clogging from chemical deposits and algae growth should be considered carefully to ensure that the correct type of device is selected. Emitters may have a built-in filter system which is able to remove some suspended material from the water flow. Self flushing emitters also have the ability to flush particles with the irrigation water.
Turbulent flow emitters (sometimes called drip tapes) regulate water flow by dissipating energy in friction against the walls of the water passage. They are less susceptible to clogging and pressure variations and unaffected by changes of water temperature within normal operating limits. Vortex emitters are less pressure sensitive than turbulent flow emitters. They are generally more susceptible to clogging by soil particles or other contaminants due to their very small water passages and need higher quality filtration and efficient management of maintenance procedures. Pressure compensating emitters (either laminar or turbulent flow devices) utilize the inlet pressure to modify the flow path size, shape or length. The pressure compensating devices are able to deliver the design flow rate over a wider range of inlet pressures. The elastomeric material used in the emitter may change its property as it ages. If the trickler is used over undulating ground where there is a variation in height along the laterals then pressure compensating emitters should be used.
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Self-flushing emitters may often be pressure compensating as well. At low pressures, up to about 0.5 bar, the emitter will flush, and at about 0.8 bar to 1 bar the emitter operates in the correct drip mode. The pump capacity and irrigation system design should be such that the system will operate correctly when the emitters are flushing. Emitters automatically self-flush, they may also be manually flushed.
Trickle irrigation systems may be installed above or below ground. On above ground installations the emission devices can be checked and visually seen to be operating, but may be damaged by either persons or animals. Growth of algae at the outlet of the emitters may occur but this depends on the design of the emission device.
Not all of the root zone of the crop needs to be wetted with trickle irrigation. The percentage of wetted area irrigated depends upon the type of crop. For wide-spaced crops, wetting may only need to cover 33 % to 50 % of the soil area, while close grown crops may require 100 % wetting of the ground area.
Trickle irrigation laterals may be installed underground using mole ploughing techniques or by individual narrow trenching. Tubing may be connected to the emitters to bring the water from the emitter up to ground level or water may pass directly from the emitter into the soil to the root zone of the crop.
Note that this does not mean that only 33 % to 50 % of the water needs to be applied. The crop still requires the same amount of water irrespective of the application method.
5.2.2 Bubblers
Laminar flow emitters (that is micro tubes, capillary tubes and spiral path emitters) are simple, reliable and inexpensive but need proper system design and operation to perform well. They are relatively pressure sensitive and are susceptible to clogging because of their low velocity flow, small path diameters and varying flow rate with temperature.
Bubblers are used to apply water either as a small stream of water or as a spray to a localized area around individual plants. Typical flow rates for bubblers range from 1 l/m to 10 l/m for solid-set bubblers. Flow rates for bubblers used on mobile irrigation systems range from 1 l/m to 80 l/m. It is possible to adjust the flow rate from some bubblers by operating the screwed adjusters fitted to them.
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Bubblers are designed to operate over a range of pressures from 0.1 bar to 1.5 bar. Bubblers fitted with pressure regulators, or of special design, may operate at higher pressures than those stated. The range of pressure regulations available for bubblers fitted with pressure regulators varies between 1.5 bar and 6 bar. Bubblers are generally used on solid-set or permanent systems, however they can be used on mobile irrigation machines such as centre pivots or linear moves. 5.3 Trickle systems 5.3.1 General Trickle systems are usually laid out permanently with the crop and comprise a control head unit and a layout of pipes fitted with emitters. Bubbler systems are laid out in a similar manner. 5.3.2 Control head This control is at the head of the irrigation system and comprises filtration, pressure, and discharge controlled fertilizer injection. Control may be by either manual or automatic valves. Manual systems usually incorporate a control valve which is opened and closed as required, by an operator, to meet the irrigation requirements. Automatic control valves may operate on a time clock, on a volumetric control valve or may be linked to operate by relating to a sensing system within the soil/crop environment. The type of filter and filtering capacity of the filter will depend upon the equipment being used and the water quality. Main filtration should be completed at the pump station. Secondary filtration should be installed at the control head, to help in ensuring that water passing to the drip laterals is free from particles causing potential blockage. Pressure regulation equipment may be required to ensure that the laterals operate at the correct pressure. Pressure regulation equipment should prevent overpressurization and potential damage to the laterals. As there is usually good uniformity of application and potentially efficient use of the water both fertilizers and other chemicals may be applied in the water. Filtration equipment should always be installed after the fertilizer or chemical injection point into the system to ensure that chemical particles do not pass through into the system.
5.3.3 Lateral layout The variation of temperature between daytime and night-time may cause the lateral tubing to expand and contract. To reduce the effects of expansion and contraction, tubing should be arranged in a snake-like form. This should ensure that emitters/bubblers stay at the location where they should be operating. Under UK climatic conditions, the variation between day and night temperatures might cause an expected expansion/contraction of the tubing up to 0.1 m per 30 m of tubing. Therefore a small amount of snaking of the tube should be sufficient. Laterals may be installed below ground level preferably deeper than 300 mm. This should eliminate expansion/contraction in the pipe and prevent the effects of sunlight damaging the tubing. Laterals should extend 1.5 m to 3 m beyond the last emitter/bubbler point on the lateral to collect any deposits which may have passed through into the system. This practice should help to prevent blockage. An allowance of 3 % extra in length for laterals should be normal practice to ensure that they are of sufficient length to irrigate the required area. 5.3.4 Emitters The number of emitters or bubblers on a lateral will depend upon the emitter or bubbler discharge, their spacing, the diameter of the lateral and the permissible pressure and flow variation within the lateral. The maximum pressure variation and its effect on flow will depend upon the type of emitter or bubbler device being used. If pressure compensating devices are used it may be possible to have a greater variation of pressure between the inlet and the end of the lateral. Normally, the variation in emitter discharge along a lateral should not be greater than ± 10 % of the nominal flow. The system discharge is determined by the maximum number of emitters/bubblers operating at any given time to satisfy the crop water requirements. Management of trickle/bubbler systems should be a simple routine as the labour requirement for operating the system is low. Normally only opening and closing of control valves is required with routine checking. Water quality for trickle/bubbler irrigation is dealt with in Part 3 3) of this British Standard. The filtration requirements of the water are critical chemically, physically and bacteriologically.
3)
In preparation.
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The potential efficiency of trickle/bubbler irrigation systems is approximately 90 %, with a correctly designed, installed and operated system. However, in practice it may be well below this figure if the system is not managed properly. Water losses may occur through the soil if excessive amounts of water are applied above the crop water requirements. However, as water need only be applied to the root zone area of the crop instead of the total soil area there is a potential here for saving water by reducing losses. Due to the low labour requirement it may be possible to operate the maximum number of h ours per day and night especially if the control valves are fully automated. The system is not affected by the climate in the same way as spray, sprinkler and gun systems.
6 Pipes and fittings 6.1 Introduction The most commonly used pipe materials in UK irrigation systems are polyvinyl chloride (PVC) pipe for underground mains and aluminium pipe for above ground mains. Other pipe materials, not so commonly used, include polyethylene pipes and asbestos cement pipes for underground mains; steel and cast iron pipes for specials; and lightweight galvanized steel pipes and polyethelene pipes for above ground mains. 6.2 General considerations
6.2.4 Plans Plans are necessary for all installations where pipelines are to be installed underground, so that a record can be available for future reference. Plans to suitable scales should be produced to provide an accurate record. 6.3 Pipe laying and reinstatement Before work starts, a record should be made of the state of the land and particular notes made of any special features so that they may be adequately reinstated if disturbed. This record should be agreed with the occupier and, wherever possible, the owner. An adequate working width should be arranged so that the construction equipment can operate satisfactorily. Temporary bridging and widening of access roads for the passage of plant and equipment may be required. Temporary fencing, access bridges and roads should be to a standard as agreed. Due attention should be paid to felled trees, top soil removal and temporary fencing. For buried pipelines, the trench width and depth should be suitable for the correct installation of the pipeline. Both the width and depth may vary according to the pipe being installed and the method used. Existing services, such as water and gas pipes, cables, cable ducts and drains, should be accurately located and the irrigation pipeline installed taking care not to affect the other services. Ditches may be crossed under or over depending on the site.
6.2.1 Introduction This clause contains recommendations on the installation of pipelines and deals with those aspects of aquisition, rights of way, construction, operation and maintenance which affect land and which are common to all applications and materials.
Special methods of construction may be required when pipelines cross canals, roads and railways.
6.2.2 Routeing
Backfilling operations should follow as closely as possible to the laying of the pipe, be well compacted and be reinstated in the proper sequence.
The choice of pipe route should be based on the equipment design and layout and the most economical route to achieve these requirements. Factors affecting routeing may include existing underground services, potential development areas, aquifers, ancient monuments, nature reserves, Areas of Outstanding Natural Beauty or Site of Special Scientific interest, trees, minerals, risk of subsidence and highly productive land. 6.2.3 Land and rights of way
Where pipelines cross or pass along a highway the exact siting and constructional details should be agreed with the highways authority.
The selection and application of valves required for pipelines will depend upon the design and specification. Reference should be made to clause 8 of this Part of this British Standard. Provision should be made at every bend, branch and dead end in a main to resist the hydraulic thrust. 6.4 Design considerations 6.4.1 Friction loss
The route may pass through land belonging to other people, and may cross roads, streams, railways, etc. For all these considerations it will be necessary to contact the other parties who may be involved.
Friction losses in pipework and fittings may be a significant part of the pressure required to operate an irrigation system. It is therefore essential that the design of the pipework and fittings is completed for correct overall system performance.
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BS 7562-5:1993
Friction losses for different pipe materials should be available from manufacturers. 6.4.2 Waterhammer and surge Both waterhammer and surge can cause problems in irrigation systems especially failure of pipelines. Waterhammer is a pressure wave which can occur when water flowing in a pipeline is s uddenly stopped, for example when a valve is closed. The intensity of the waterhammer can be severe and depends upon the valve closing time, the water velocity and the length of the pipeline involved. ` ` , , ` ` ` , , , ` ` , ` ` ` , ` ` , ` ` ` ` ` ` , ` ` , ` ` , , ` , , ` , ` , , ` -
Surge in pipelines is the mass movement of water, often as a result of waterhammer, and can occur, for example, when a pump suddenly stops as a result of power failure. If the irrigation system is designed and operated with velocities of less than 1.5 m/s in the pipeline, the risk of waterhammer and surge is reduced, although not eliminated. The total pressure in pipelines includes the operating pressure of the pipeline and the additional pressure caused by potential waterhammer or surge. Waterhammer and surge may be reduced by one or more of the following methods. Reducing the effective length of the pipeline by the incorporation of more valves of a suitable specification in the line. Reducing the velocity. Increasing the closing time of the valve. Installing suitable pressure regulating valves. Installing suitable air valves. 6.4.3 Thrust blocks
Plastics pipes have good hydraulic characteristics resulting in low frictional losses and high flow capacities. They will not corrode in contact with water ensuring that their good hydraulic characteristics are maintained throughout their life. The coefficients of expansion of plastics materials are generally much greater than those of metals and particular care should be taken in the design of pipework layouts above ground. Plastics are resistant to many chemicals and are thus suitable for installation in aggressive soils. Some of the materials are degraded by exposure to direct sunlight unless their composition includes additives to resist the effects of sunlight. 6.5.2 installing buried pipes Pipe with diameters up to 150 mm can be jointed on the surface and subsequently arranged in a snake-like form in the trench, this eliminates the need for wide trenches. Plastics pipes may also be mole-ploughed into the ground. Good trenching practices should be followed to achieve correct installation of the pipe, including bedding, side filling and backfilling. 6.5.3 Testing After installation it is essential that all pipework, fittings and appliances be inspected and tested hydraulically to ensure the safety and efficiency of the system. Before the start of any test the system should be visually inspected to ensure that the pipework has been correctly installed. The test procedure followed should be as recommended by the manufacturer or as stipulated by the approving authority.
Pipelines operating under pressure can be subject to movement caused by thrust forces, at any change in direction or termination. External anchorage should be provided, usually in the form of concrete thrust blocks, to resist the thrust forces.
6.5.4 Limitations
External anchorage should be provided at all changes in direction and at points where termination of water flow may occur Thrust blocks are therefore recommended at all tees, end caps, bends, valves, etc.
Provision should be made for emptying pipes in exposed positions above ground or shallow buried pipes if they are not otherwise protected against frost damage.
6.5 Plastics pipework (thermoplastic material) 6.5.1 General principles and choice of materials Materials considered here include unplasticized PVC pipe (for cold water services), low density polyethylene and high density polyethylene pipe.
Plastics are not conductors of electricity and therefore no attempt should be made to use the pipework as a means of earthing electrical equipment.
6.5.5 Unplasticized PVC pipe Above 20 ° C water temperature and ambient temperature unplasticized PVC pipe (PVC-U) should be derated according to the manufacturer’s recommendations.
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PVC-U pipe may be supplied plain ended for jointing with separate couplings or supplied with integral sockets already formed on one end of each pipe. Joints may be solvent cement, push fit insertion or mechanical joint. Both push fit and mechanical joints offer little resistance to end thrust forces such as those set up at bends, junctions, valves, etc. The pipeline therefore should be suitably anchored when these joints are used. The correct methods for completing the jointing of pipes and fittings as advised by the manu facturer should be followed. Either saddles or tees may be used for service connections, the choice of the most suitable for each situation depends upon diameters used and site conditions. Cold bending or hot bending of PVC-U pipes may be applied to allow changes in direction; either method requires skill. The storage, handling and transport of PVC-U pipe should be as recommended by the PVC-U pipe manufacturer, taking care to protect against the effects of prolonged exposure to sunlight. Installation of PVC-U pipe below and above ground should follow the manufacturer’s instructions. For above ground installations preventive measures should be taken to reduce the effects of freezing, expansion and heat and adequate support should be provided. Before testing, anchor blocks should be allowed sufficient time to develop their strength, e.g. concrete to set properly. All intermediate control valves should be positioned open for the duration of the test. The test should be deemed satisfactory if the quantity of water required to restore the required test pressure does not exceed the amount recommended. The recommendation in the UK is as follows. 3 l per 1 000 m of pipe per 25 mm of nominal bore, per 3 bar of test pressure per 24 h. Refer to BS 8010-1 for assessing the suitability of soil for surrounding buried pipes. Details of working pressures, classes and wall thicknesses of PVC-U pipes may be found in the manufacturers’ technical data. 6.5.6 Polyethylene plastics pipe 6.5.6.1 Low and high density polyethylene plastics pipe Low density polyethylene (LDPE) has a relatively low tensile strength and pressure pipes made from it are generally restricted to those of smaller bore.
High density polyethylene (HDPE) is rather stiffer and is a stronger material. Therefore the pipe walls are thinner and larger bore pipes at the higher pressure classifications are possible. Polyethylene is not liable to attack from water or from soils which are corrosive to metals. Polyethylene is an electrical insulator and cannot be used for earthing electrical insulations. Polyethylene softens with heat and it is essential that it is not used for applications adjacent to heated surfaces. LDPE softens at lower temperatures than HDPE. Polyethylene pipe may be laid in exposed positions without the need for special protection against frost damage, but will not prevent the water from freezing in the pipe. The outside diameters of the pipes are based on the outside diameters of steel pipes. Polyethylene pipe may be jointed using thermofusion techniques, compression joints, or threaded joints. Bending of polyethylene pipe may be by either hot or cold techniques, hot techniques achieve tighter bends. Polyethylene pipe may be laid satisfactorily by mole-plough providing the equipment is capable of maintaining the correct depth of cover over the pipe. The piping is liable to be cut by sharp surfaces above or below ground and therefore extreme care should be taken. 6.5.6.2 Medium density polyethylene pipe It is a recommendation of the UK water industry that the use of blue medium density polyethylene pipe (MDPE) be adopted as the standard type of polyethylene pipe for underground water services in the size range up to and including 63 mm. In the size range over 63 mm the use of MDPE pipes is a matter of choice for the engineer and the end user. In this range of sizes MDPE piping is often compared with PVC piping for both cost and physical advantages. ` , , ` , ` , , ` , , ` ` , ` ` , ` ` ` ` ` ` , ` ` , ` ` ` , ` ` , , , ` ` ` , , ` ` -
Although these recommendations do not apply to agricultural irrigation systems, the engineer or the end user may specify MDPE pipe. Pipes up to and including 63 mm may be supplied in coils up to 150 m long, while pipes larger than 63 mm may be supplied in 6 m, 9 m or 12 m lengths. Jointing methods vary depending on the pipe diameter, but they include compression fittings, electrofusion methods and insert fittings.
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BS 7562-5:1993
6.6 Aluminium pipe Aluminium pipe may be used for many above ground applications including portable supply mains, portable sprinkler lateral lines, and suction and delivery pipework on the pump unit. The pressure rating of an aluminium pipe depends on its diameter, in general, the smaller the diameter of the pipe the greater is the maximum operating pressure that can be used for the system. Typical operating pressures are up to 12 bar for pipe diameters up to 125 mm to 150 mm, and up to 9 bar for diameters above 150 mm. High pressure irrigation systems may eliminate the use of aluminium pipe. Friction loss in aluminium pipe is greater than in PVC pipe due to the slightly rougher surface finish of the pipe. Friction losses in the fittings vary according to the type of connection and the degree of resistance to flow that occurs. The maximum advisable velocity in aluminium above ground portable pipe systems is about 1.5 m/s depending upon system design parameters. A velocity may be used above this figure, provided that suitable precautions are taken in the design and specification of the pipe and fittings used. The technical specification for aluminium pipe should detail wall thickness, wall tolerance, mean diameter, tolerance on mean diameter, bursting pressure, sag when full and denting factor Reference should be made to the manufacturer to ensure suitability for the application. Pipe couplings used with aluminium pipe may be quick couplers, flanged or sleeved. Quick couplers, using a male and a female coupling to provide a connection between the lengths of pipe, should be easy to connect and disconnect and have efficient seals. The seals may drain down automatically when pumping stops, facilitating pipe moving. Seals may be fast drain or slow drain, the selection of the correct type should be made to suit the application. Flanged couplings provide a more permanent type of connection and would not usually be used in portable pipe systems. Sleeve couplers (bolt up wedge type) may be used for the connection of aluminium piping. The sleeve coupler slides over the two plain ends of the pipe and bolts up to provide the seal connection. This type of coupling is more often used on the su ction pipe for the pump unit where aluminium piping is employed. In this application it is essential that the seals do not allow air to enter.
The weight of aluminium pipe compared with lightweight galvanized steel piping is about 50 % of the weight of lightweight galvanized steel. Aluminium pipes are therefore suitable for moving and installing by one man even with the larger diameters of pipe. The loading capabilities of aluminium pipe are low and when the pipework has to span even a short distance, support should be provided underneath the pipe. The spacing and the type of supports depend upon the pipe diameter. Aluminium pipe is susceptible to corrosion from certain chemicals; copper may be especially damaging to aluminium pipe. It is a soft metal and therefore physical damage may easily occur if roughly handled. 6.7 Lightweight galvanized steel pipe Lightweight galvanized steel pipes may be used for both portable supply mains and sprinkler lateral lines. This type of pipe may also be used for suction and delivery pipes on pump units. A typical pressure rating for lightweight galvanized steel piping is a working pressure of 15 bar for pipe diameters up to 216 mm. The pipe may be suitable for higher pressure systems. Friction loss characteristics of lightweight galvanized steel piping are similar to losses in aluminium pipe unless corrosion has occurred inside the steel piping. The material for lightweight galvanized steel piping is specified by the manufacturer and should be to a suitable specification for irrigation applications. The commonly used couplings on this type of pipe are over centre latch couplers. A seal is achieved by levers holding the coupling tight and preventing any water loss. The angle of deviation for lightweight galvanized steel pipes is usually 15° either side of the straight line position. The seal provides effective sealing under vacuum and is suitable for the quick coupling connections required on portable suction assemblies. Galvanized steel piping, if damaged on the galvanizing, is subject to corrosion and once the steel is exposed, rusting may occur. The quality of the thickness and application method of the galvanizing is important for the pipe to ensure a long service life. If the pipe is moved around continually on abrasive soils then the galvanizing may well be worn away and the steel exposed and corrosion could occur. Alternative pipe materials should be considered.
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6.8 Steel pipe Steel pipe is commonly used in suction and delivery assemblies for pump units, in road crossings, hydrant risers and other applications both underground and above ground. It is relatively inflexible and connection of fittings should be made with care especially where potential movement may occur. Joints that may be used for steel pipe include sealing ring joints, flanges, butt welding, sleeve joints and threads. The purchaser or designer should state whether the pipes and specials are to be protected against corrosion, whether the protection is to be external, internal or both, and the type or types of protection required. The types of coating commonly used in irrigation systems are bitumen applied hot or cold, epoxy or plastics based coatings, cold galvafroiding or equivalent. Steel may be used to fabricate specials such as bends, tees and reducers for certain types of irrigation fittings. 6.9 Pipe fittings The fittings described concentrate on those used for PVC pipe as this is the commonest type of material used for underground mains pipelines for irrigation systems in the UK. Fittings for underground mains may be made from PVC material, cast iron, ductile iron, aluminium or steel.
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The suitability of a specific material for the application required will depend on the application in the field, manufacturer’s advice and customers’ preferences. The type of material used for the fittings will also affect the method of installation, ease of installation and resistance of the fitting to corrosion, etc. Fittings may be complete with couplings or may be plain ended to be joined to PVC pipe or other fittings using separate couplings. Fittings complete with couplings are usually either cement joint (PVC), or mechanical joint (PVC fitting and joint or ductile iron, cast iron or aluminium). The use of cement joint fittings is not recommended on fittings above 100 mm to 150 mm as it is likely that the cement applied to the fitting will have partially dried before the fittings can be connected together. It is therefore advisable that mechanical joints are used above 100 mm to 150 mm sizes where seals make the joint instead of cement.
Separate couplings usually employ a mechanical joint to provide the connection between the two plain ends of pipe and fittings. Bolt up wedge type couplers are often used for connecting PVC pipe and either steel fittings or cast iron fittings. The seal is achieved by tightening up wedges by clamps onto the two pieces of pipe or fitting. These types of couplers may connect different outside diameter pipes and fittings (stepped couplers). The coupler may be fitted with or without a centre register. Couplings without a centre register are used for repair of piping which is already installed in the ground. It is possible to slide the coupler all the way over the one section of pipe and then slide it back over the two sections of pipe to repair coupling. Push on couplers use a wedge seal at either end which seals automatically. Connections between plain ended PVC pipe and flanges may be achieved by using either a flange adaptor which incorporates a bolt up wedge seal assembly or a stub flange which is cemented to the PVC pipe itself. For smaller diameter pipes, unions may be used to provide a connection between PVC pipe and the fitting. Threaded unions cement joint onto the PVC pipe and thread connect onto the fitting (valve, tee, etc.). Bends may be fitted with or without couplings for connection to the PVC pipe. Bends may be either short radius, long radius or sweep bends. Sweep bends or long radius bends are preferred for use on the larger diameters of pipe involved in PVC supply mains, giving better flow characteristics and less loss within the bend. Short radius bends may be used on the smaller diameter sizes of pipe but care should be taken in their application. The normal bend angles available are 90°, 45° and 22.5°. Tees may be provided with or without couplings and may have different connection types on their inlet and outlet. A typical application for tees within the underground mains would be where a spur connects to the main line. The tee may have either cement joints or mechanical joints if it is PVC or may use mechanical couplings if the tee is of steel, cast iron, etc.
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Hydrant tees provide the take off in a vertical direction to above ground irrigation equipment. The connection to the above ground fitting is usually threaded on the smaller diameters and flanged on the larger diameters. The type of material from which the hydrant is made should be considered carefully in relation to the application of the connected item to the hydrant tee. On the larger diameter hydrant tee take offs, such as 75 mm where a hydrant valve is fitted to the top, it is usual to use a steel or cast iron hydrant tee. This material should give greater strength and support to the hydrant riser and reduce the risk of damage to the tee connection. Smaller diameter take offs may be connected to PVC hydrant tees and the riser may then be of PVC material to below ground level or it may be a threaded steel connection. ` ` , , ` ` ` , , , ` ` , ` ` ` , ` ` , ` ` ` ` ` ` , ` ` , ` ` , , ` , , ` , ` , , ` -
The material used for reducers or increasers depends upon the diameter of pipe used and also the application to which the piping is put. Reducers and increasers may be made of PVC, cast iron, ductile iron, aluminium or steel. Where reducers are used, such as reducing bushes, a ccount should be taken of the friction characteristics of the reducer caused by the sudden reduction of diameter on the reduction side of the fitting. In the larger diameter main line pipes, long reducers should be used, providing a gradual reduction of size. End caps may be fitted at the ends of pipelines where valves or other assemblies are not utilized. The end cap may be of PVC, either mechanically jointed or cement jointed to the PVC pipe. Saddles may be fitted to the PVC pipe to provide the take off connection to either small diameter laterals or to above ground positions. The saddle may be constructed of either PVC or gunmetal. PVC saddles may be either threaded or provide a cement joint connection for PVC pipe or for other materials. Gunmetal saddles are usually threaded for connection to their offtakes. The type of saddle used and its installation should be considered carefully to ensure that the take off will perform correctly.
7 Suction and delivery pipework 7.1 Suction pipework The selection of the suction fittings required for the pump unit will depend upon the type of water source, the specific conditions existing in that water source and the portability required for the assembly. The pipe diameter used for the suction should be of the correct size to keep the friction losses as low as possible and practicable. The longer the suction pipework the more critical will be the size of the suction pipe and fittings.
The radius of the fittings used should be generous and sweep bends should always be u sed, in order to discourage excessive turbulence in the water being pumped. The lengths of suction pipe used should be kept as short as possible to reduce friction losses in the suction pipework. The pipe connections (flanges, threads or couplings) should be kept to as few as possible, reducing the risk of air entering the suction line at the joints and limiting the friction losses caused by the connections. Valves should only be used in the suction line where there is positive suction head. The valve should be the straight through type and should present no resistance to flow when fully open. Fittings and valves which include bends, tees, etc. should be fitted near the pump suction inlet. The number of fittings used in the suction assembly should be kept to as few as possible. Where it is necessary to reduce the diameter of the suction pipe to connect to the pump suction flange an eccentric taper should be used. This reduces the risk of air entering the pump and air being trapped in a potential high point of the suction piping. The suction pipe inlet should either have a bell mouth or a suitable taper to reduce the entrance losses, where a footvalve is not fitted. A suction strainer may be fitted to the end of the suction pipe. This should prevent large debris from entering the pipe. The maximum inlet size should be such that particles that pass through will not cause damage to the pump. A footvalve may be used in the suction to facilitate priming of the pipework. Trash screens, where used, should have sufficient surface area to ensure that the velocity of water through the trash screens is less than approximately 0.3 m/s for efficient operation of the screens. Straight pipe approximately 5 to 6 times the diameter of the pipe should connect from the suction bend onto the eccentric taper prior to the pump suction flange. A vacuum gauge (if fitted) should be operated by a gauge cock underneath to provide isolation for the gauge. A water level sensor unit may be installed in the water source to signal high and low water level in the source to the pump starter panel. The inlet to the suction pipe should be at the recommended submergence depth below the water level.
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BS 7562-5:1993
The suction pipework should be installed so that it rises gradually from the water source to the pump. There should be no high spots in the suction pipework where air could be trapped resulting in reduced flow through the pipe. The velocity of water in the suction pipe should be kept to below 1.5 m/s. A floating suction intake (where used) has its inlet to the suction pipe sited just below the surface level of the water. This location should reduce the amount of contaminants entering the suction pipe because this point is usually where the cleanest water is situated. The suction intake should be located at the correct minimum distance away from walls, baffles and other such pipes to ensure correct performance. Both horizontal and vertical pipes should be well supported. If the suction pipe passes through a wall close to the pump connection, a flexible coupling may be used to connect from the pump to the suction pipework. The flexible coupling reduces the transfer of vibration and makes access to the pump connection and suction fittings easier. 7.2 Delivery pipework The delivery fittings should be designed and specified to carry out the functions required. These functions may include control of the flow and pressure, measurement of the flow, and protection of the system. Installation of both the valves and the pipe and fittings should be designed correctly to achieve optimum system performance. If the pump delivery flange has a different diameter from that of the delivery valves, a concentric taper should be used. This taper should have a smooth gradual transition in size to the diameter of the valves to keep the friction loss to a minimum. A non-return valve should be installed adjacent to the concentric taper to prevent flow reversal. The non-return valve should be of the non-slam type to avoid the risk of potential damage that could be caused by waterhammer.
A pressure relief valve, which might be fitted either on the top of the non-return valve or to a separate tee, may be installed in the delivery fittings, to provide protection and flow bypass facilities. An air/vacuum relief valve may be installed to expell air from the mains while the pipework is filled and to allow air to enter when pumping stops. A pressure gauge may be installed on the delivery side of the pump unit, in such a position that it does not give inaccurate readings due to turbulence in the pipework. A gauge cock should be fitted underneath the pressure gauge to provide isolation. Structural support should be provided for all the fittings and valves to ensure that no weight is put onto the delivery connection of the pump. Clamps fitted around the pipework should ensure that it cannot move. Thrust blocks should be provided at the calculation design points connecting from the delivery fittings into the supply mains. Thrust blocks should be used at all changes of direction both horizontal and vertical. Motor vibration is common on internal combustion engine powered pumps and if transmitted to fittings and supports could cause their failure. To avoid a transfer of motor vibration from the motor to the fittings it may be advisable to u se a suitable adaptor or flexible coupling.
8 Valves 8.1 Pressure regulating valves The function of pressure regulating valves is to control and regulate a higher upstream pressure to a lower downstream regulated pressure.
They are used on the delivery side of a pump unit and should maintain a preset regulated downstream pressure at all times even if the demand from the irrigation system varies according to the irrigation equipment being operated.
It may be possible to fit a pressure relief valve, by tapping into the top plate on the non-return valve.
Valve sizing is critical for long life and minimum wear and tear. A pressure regulating valve should never be oversized because control of pressure is achieved by the throttling of the water that is passing through the valve and seat.
A flow control valve to open and close the flow to the irrigation system often uses a manually operated isolating valve.
Bends, undersize pipe and all restrictions should not be installed either on the inlet or outlet side of a pressure regulator.
A flow regulating/pressure regulating control valve may be required for the irrigation system, to automatically regulate the flow and pressure downstream of the valve.
An isolating valve may be installed each side of a pressure regulating valve so that the latter can be easily removed for maintenance without draining the entire pipe system.
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Pressure gauges should be used, one on the upstream and one on the downstream side of a regulating valve and as near to the valve as possible.
8.3 Surge valves
Dirt, pipe scale or other foreign matter should be prevented from entering and fouling the valve. The water quality should be checked to make sure that the regulator will operate correctly and if necessary a filter should be installed on the u pstream side of the valve. The water quality may affect the decision as to which type of regulating valve is selected.
The function of surge valves is to protect the irrigation system against surge. They are designed to open and release water from the pipeline before surge can cause damage.
The accuracy of pressure regulation downstream of the valve should be better than ± 5 %. If a secondary pressure sensor line is used in conjunction with the valve, a better accuracy should be achieved. 8.2 Air valves Air valves allow air to enter and be expelled from a pipeline. The main applications include: allowing air to escape when filling the pipeline with water; allowing air to enter the pipeline when draining the system; removing air pockets at high points on a pipeline caused by entrained or dissolved air; preventing negative (suction) pressures during main system shut down. Air valves may need to be sited in the following positions in the irrigation system: shortly after the pump discharge valve a double air valve may be fitted, where a peak in the pipeline occurs;
Surge is the sudden mass movement of water in a pipeline which can occur when there is a failure of the pumping system.
Applications may be varied according to the specification and build of the valve. These applications may include: to open fast at a preset pressure to dissipate damaging surge pressures; to close at an adjustable speed when pressure reduces below a preset setting; to open fast when anticipating surge on a preset subnormal pressure; to stay open until surge is cleared and close when normal pressure is restored. The surge valve is usually sited in the pump delivery fittings downstream of the main valves to provide protection for the mains, valves and pump. The valve sizing required should be calculated taking account of the functions to be served by the valve. An isolation valve should be fitted upstream of the surge valve to provide the facility for maintenance of the surge valve. A discharge pipe should be fitted to the downstream side of the surge valve to take water either back to the water source or to a convenient drainage point. This pipe should be open to atmosphere. 8.4 Flushing valves
where the pipeline is parallel to the hydraulic gradient a double orifice valve may be fitted at each end of the section;
The function of flushing valves is to allow dirt particles and other contaminating matter (even rodents) to be washed out of the system.
where straight sections of pipeline occur they also require venting at suitable regular intervals;
Flushing valves should be sited at the ends of supply mains and at the ends of spurs. They may also be installed at the ends of laterals and header pipes depending on the type of irrigation system and its requirements.
where a change in downward slope occurs a small orifice air valve may be fitted. The size of air valves should be calculated taking account of the diameter of the supply mains and the speed at which the air is expelled. There are two main types of air valve, small orifice or large orifice, both may be used in the irrigation system. Small orifice air valves should be installed to allow expulsion of air while the system is operating. Large orifice air valves allow air to be expelled from the main or for air to enter quickly.
8.5 Drain valves The function of drain valves is to enable the system pipework to be drained, providing protection against damage from water freezing in the pipework and to allow repair or maintenance to be completed. Drain valves should be installed at all low points. The drain valves should be able to drain the complete system including suction and delivery fittings, supply mains and in-field equipment.
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BS 7562-5:1993
The drainage water from the drain valve should either pass into a soakaway or be fed via a pipe into a surface water course or ditch. Access to underground drain valves should be via a valve chamber and a key to operate the valve. 8.6 Riser valves and hydrants The function of riser valves or hydrants is to provide a take-off to irrigation equipment, or a sub-main , from either an above ground or underground supply mains. The operating pressure ranges over which the hydrant valve will operate should be considered to make sure that it is suitable for the application. The friction loss through the hydrant valve should be known to ensure that the design diameter is correct for the duties to be performed.
Brass valves are more expensive but may provide greater strength and corrosion resistance. If the valve is fitted with a pressure regulation facility, a pressure difference is required between the inlet and outlet, varying from 0.5 bar to 1.0 bar, for these valves to operate successfully. The aim of the pressure regulating facility is to maintain a constant outlet pressure downstream of the valve, within ± 0.3 bar. A Schrader valve installed on the side of the valve provides the facility for checking the pressure setting of the valve. Alternatively, a pressure gauge assembly may be fitted to the valve, providing an instant readout of the pressure.
The opening and closing of the valve should be possible without causing damage either to equipment or to persons operating the valve.
A grit filter may be fitted to the valve to prevent debris from jamming the solenoid plunger and causing it to fall to operate. A mainstream filter may be fitted, commonly constructed of a nylon screen. This is able to filter water entering the bonnet cavity of the valve.
8.7 Volumetric control valves
8.8.3 Hydraulically operated valves
The function of metering valves is to automatically shut off the flow after delivering a preset volume of water, regardless of changing pressure or flow rate.
The functions that hydraulically operated valves are able to carry out are similar to those of an electric automatic valve.
The manufacturer’s recommendations for maximum and minimum flow rates through the valve should be followed to ensure that the valve will deliver the required volume of water and accurately measure the flow passed.
Location limits apply to these types of valves for both the distance from the controller that they can be sited and the height above or below the controller position.
The volumetric valve may be fitted with the facility to sequentially operate and regulate the downstream pressure. The installation of the valve may require straight lengths of pipe both upstream and downstream of the valve. The valve opening and closing times may be adjustable and should be such that waterhammer and surges in the line are discouraged. 8.8 Automatic valves
Operating distance away from the controller will vary according to the manufacturer’s specification. Normally open valves may be installed up to approximately 300 m from the controller while normally closed valves may be installed up to approximately 60 m from the controller. 8.8.4 Mechanically operated valves Similarly, the function of mechanically operated valves is to provide on/off control of flow. 8.9 Controllers The main function of controllers is to automatically open and close control valves. Controllers may be used to open and close valves operating irrigation laterals, to work in conjunction with flushing valves on filter units and to perform other specialist duties.
8.8.1 General Automatic valves may be operated electrically, hydraulically or mechanically. 8.8.2 Electric automatic valves The function of electric automatic valves is to provide on/off control of flow. The applications for all electric automatic valves are wide and include automatic flushing for filter units, automatic drain down of systems, and many other uses. Electric automatic valves may be used to control the flow to sprinkler or drip irrigation laterals or to centre pivot or other similar equipment.
A controller to be used on an agricultural irrigation system needs to be versatile and may include features such as the number of stations operated, the time of operation per station, day and hour programming, and multi or split cycle programming. Pump switches, cancel switches, rain switches, master valve control and moisture control circuits may also be required and utilized within the control system.
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8.10 Valve boxes All remote control valves, manual control valves, isolation valves, etc. should be installed in valve access boxes made of concrete, thermoplastics or other suitable material. The valve box should provide protection for the valve and should be of adequate size to allow access to the valve for operation, maintenance and repair. There should be enough room to allow removal of the valve and access to the connectors each side of the valve. The valve box should be installed on a suitable base of gravel to provide a sound foundation for the box and to facilitate its easy levelling so as to provide proper drainage. The valve box housing should be so constructed that it will rest on bedding and not interfere with pipes and cables entering or leaving the valve box. The housing should be strong enough to s upport the cover. The valve box should be provided with length and side extensions if it is required to bring the valve box level with the finished ground level, rather than burying the valve box below ground. The box should be supplied with an approved cast iron, concrete or thermoplastics cover. The cover should be of sufficient strength to resist failure due to foreseeable causes, such as a vehicle driving over it.
9 Flow meters 9.1 General The function of flow meters is to measure the discharge from the pipeline or volume of water passing along the pipeline. They may indicate the flow rate and/or the volume. The minimum and maximum flows that a flow meter will handle accurately are indicated by the manufacturer It may be possible to operate at lower and higher flow rates than those indicated but the manufacturer should be consulted. The usual accuracy range for flow rate measurements for irrigation flow meters is ± 2 %. There are two flow measuring methods normally used for irrigation systems in the UK; the mechanical propeller type and the ultrasonic type. 9.2 Propeller flow meters The propeller should be designed so that debris is not able to block the impeller and cause it to operate incorrectly. The impeller should be resistant to corrosion and wear as should the drive beatings.
The meter readout on the dial may have a lockable cover which provides additional protection. It should also be fitted with anti-condensation glass so that the inside does not fog up. For correct installation and operation of the meter, the pipeline should be full of water at all times, the flow meter should be installed with the correct direction of flow, and upstream of the flow m eter there should be the equivalent of 10 pipe diameters of straight pipe without fittings or flanges. Downstream of the flow meter there should be the equivalent of at least 1 pipe diameter free from valves, fittings or flanges. It may be advisable to install the flow meter on the suction side of the pump unit where there may be less turbulence and thus greater accuracy of recording. 9.3 Ultrasonic flow meters The velocity range over which the ultrasonic flow meter will operate accurately depends upon the manufacturer but the average range is 0.3 m/s to 0.5 m/s. An ultrasonic flow meter has no moving parts and operates with a flow sensor which fits externally to the required diameter of tube and is complete with a tube assembly. The flow converter transmitter may be connected to the length of pipe onto which the flow sensor is fitted or it may be sited up to a maximum distance of 20 m to 30 m away from the sensor. This type of meter may be more suitable for flow measurement of irrigation water containing debris and other contaminants.
10 Pump installations 10.1 Permanent pump installations Permanent pump installations should be considered where either electric motor driven pumps or internal combustion engine driven pumps are to be located and operated at one point, e.g. abstraction from a reservoir or borehole. Permanent installations may provide benefits of security and better system reliability. Adequate space should be allowed around the pump and fittings to make servicing and maintenance easier. A fuel storage tank may be required for a diesel engine driven pump. The storage tank should be sited outside the pump house. There should be a bund constructed around the tank so that if there is a spillage no pollution of water sources or other areas would occur.
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An electrical motor driven pump requires an electricity supply. The electricity authority may advise on the siting of the step-down transformer and the main switch gear and isolators. The location of the pump starter gear within the pumphouse should be such that the operator can reach this equipment as soon as he enters the pump house. All the equipment sited at the pump station should be adequately protected from the weather. Rain, water and moisture should be prevented from entering motors and electrical equipment. Direct sun onto the motor or pump should be avoided as this could lead to overheating. The Health and Safety at Work etc. Act 1974 [1] applies within the pump house, and is applicable to not just moving parts but electrical and other components. The floor surface should be solid, even, of non-slip construction and should not become slippery. A concrete brushed surface should be safe. There should be no pipes, cables, valves or fittings in the access areas that could present a hazard to the operator. Piping and other fittings, where possible, should be installed below ground level and suitable covers placed over fittings that are within the operator access areas.
Air moisture condensing on components may cause corrosion. The fittings should be s uitably protected. A space heater may assist in reducing condensation. The pump base should be suitably constructed of concrete, reinforced where necessary, to the specified size, dimensions and depth. The concrete foundations for the pump and motor should be such that both the pump and motor are raised off the ground by at least 150 mm. A return blow-off pipe for the pressure relief valve should be installed from the pressure relief valve back to the water source. This pipe should be of sufficient diameter to allow the pressure relief valve to operate correctly. If a hand priming pump is used to prime the pump, a return pipe or a return gulley should take the water that is discharged from the hand priming pump back to the water source or drain. Fertilizer injection equipment and filtration equipment may be sited within the pump hous e. Both will need regular maintenance and therefore easy access to this equipment is important. 10.2 Portable pump installations
The pump house should be adequately ventilated so that the equipment does not operate in extremes of temperature or humidity.
Portable pump installations are generally designed for irrigation pump units which are to be re-sited fairly frequently, often during the irrigation cycle. Mobility is therefore a key factor in this type of installation.
The lighting in the pump house should be adequate for the operator to work and for maintenance work to be carried out. Light may be from a combination of both natural and artificial sources.
Small light pump units may be mounted on a simple base and supplied with a handle for hand carrying. Larger units may be mounted on a wheeled trolley assembly so that the unit can be towed.
It may be necessary to install overhead gantry gear to assist in removal and/or installation of the pump and motor for repair and maintenance. The need for lifting gear depends upon the size of the equipment installed.
If the pumpset is to be towed and is mounted on wheels, jacks should be fitted to provide stability when pumping.
Drainage gulleys should be constructed in the floor of the pump house to allow any water to run out of the pump house into a soakaway or drain. Water may drip from packed glands or it may leak from the pipework. The floor should slope slightly so that water can run off into the drainage gulleys. Where chemicals are used (e.g. via chemical injection equipment) they should be stored in a secure area, away from water and the pump house, preferably in a separate building. Drain down facilities should be fitted to the suction and delivery pipework and pumping and other equipment to ensure that water can be drained from the equipment when not in use. This should prevent the risk of damage caused by freezing.
For ease of connection and disconnection the couplings on the pump unit should be of the quick connect and disconnect type. The quick couplings on the suction side should provide complete sealing under vacuum so that air cannot enter the suction via these couplings. Quick couplings used on the delivery side of the pump should be of the type that will seal under pressure and will not leak when the system is operating. The suction assembly should incorporate quick coupling at the pump, and be portable and easy to move. It should be possible to drain the suction hose and pipe by opening a valve on the f oot valve, thus facilitating re-siting. The portable pump unit should be positioned so that it is not able to move, especially towards the water source, while it is pumping.
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BS 7562-5:1993
The pump unit should be protected against a back flow of water in the mains, which could occur when the system stops pumping. This protection should be provided by a non-return valve fitted in the first piping in the supply mains and protected against thrust forces. A diesel engine pumpset may require a portable fuel tank, unless a fuel tank is built into the pumpset. Both the suction and delivery pipes should be supported adequately to prevent excessive weights being placed on the suction and delivery connections of the pump. The suction pipe should be installed so that it rises slowly from the water source up to the pump inlet. 10.3 Floating pumps Floating pumps may be used on surface water sources where the site conditions are suitable, e.g. where there is great variation between maximum and minimum water levels in the water source, such as in a reservoir with a water level variation greater than 5 m. The normal power unit to drive a floating pump unit is an electric motor, as an electrical supply is usually easier than supplying fuel for an internal combustion engine. The floating unit should be constructed so that it is stable and will support the weight of the pump and accessories. The floating pump should be anchored securely so that it will not be able to detach itself f rom its moorings. The motor specification should be suitable for operating in the adverse conditions which may exist at a floating pump installation. The cable should be correctly rated and be supported with adequate fixings. The delivery pipe from the pump unit to land may be by either solid or flexible pipe. Whichever type of pipe is used, it should allow vertical pump movement without straining the connections. Access to the pump should allow repairs and maintenance to be carried out.
The minimum safe flow that the pump will handle is critical for the protection and performance of the pump. The pump manufacturer should advise on this minimum safe flow referring to temperature rise, effect on performance and nett positive suction head required. A bypass assembly or orifice plate may be used to allow the pump to operate under low flow conditions. The maximum flow that the pump will handle may be critical in the selection and sizing of the power unit. The sizing depends on the control and range of duties that may be demanded. Motor overloading should be avoided by the correct design and selection of the pump and motor. 10.4.1.2 Total dynamic head The total dynamic head should be evaluated in terms of the duty head and the shut down head i.e. when equipment is no longer operating and there is no flow. The duty head may vary according to where the in-field equipment is being operated. The static head, the head loss in the main s and the equipment operating pressure may all vary, thus changing the operating duty head at the pump. The pump shut down head should be considered when selecting pumps as well as the irrigation system design requirement. Protection equipment may be needed to prevent overload occurring due to high shut down head which may be greater than the normal operating head. 10.4.1.3 Efficiency The efficiency of the pump unit is directly related to the power required for the pump. Efficiency should be as high as possible at the duty point. If a pump has to operate over a wide range of pressures and discharges, variations in efficiency can be expected. 10.4.1.4 Absorbed power The absorbed power required at the pump shaft will vary if there is a range of pump duties to be met. The selection of the power unit should be based on the range of duties required plus a factor for safety and wear and tear.
10.4 Pumps
10.4.1.5 Nett positive suction head required
10.4.1 Centrifugal pumps
The nett positive suction head required (NPSHR) is the pressure required at the inlet of the pump to achieve the specified duty. It is a function of the pump inlet design and impeller speed. (NPSHR) varies with the type and size of pump and increases with both discharge and pump speed. NPSHR curves should be given on the manufacturer’s pump performance data sheets, covering the range of speeds at which pump performance is shown on the curves.
NOTE Most of the pumps used for irrigation are centrifugal pumps.
10.4.1.1 Discharge Many irrigation systems operate over a range of flows, rather than at one fixed duty point depending on the equipment, operation and type of irrigation system. Where a wide range of flows is needed it may be necessary to install more than one pump unit and operate them in parallel.
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10.4.1.6 Nett positive suction head available The nett positive suction head available (NPSHA) is the resultant pressure at the entrance to the pump impeller after all losses and performance requirements have been met. The NPSHA shou ld be positive otherwise the pump unit will not operate. 10.4.1.7 Pump unit configuration Where more than one pump unit is used in the irrigation system, they may be operated in series or in parallel. Pumps operating in series use a first pump which supplies water under pressure to a second pump. The second pump delivers the same discharge but boosts the pressure. It is essential that the pumps are balanced with regard to discharge. The maximum casing pressure of the booster pump should be capable of handling the total pressure produced. Pumps operating in parallel combine to increase the discharge whilst the pressure remains the same. The pressure produced by each pump should be similar to ensure balanced pumping from all the pumps.
Submersible pumps are electrically driven. For correct installation and performance of the pump, the factors considered should include maintenance, borehole straightness, removal for servicing, operating depth and depth of water above the pump. For all boreholes there should be close liaison between the borehole engineer and the pump supplier to ensure that all features of the borehole are assessed. 10.5 Power units 10.5.1 General The power unit may be either an electric motor, an internal combustion engine or a PTO shaft, depending on the type of pump. The choice between the alternatives depends on many factors both on site and with regard to the client’s requirements. Economic factors also apply: both fixed costs and variable cost elements need to be considered carefully when selecting the power unit. 10.5.2 Electric motors
10.4.1.8 Cavitation
Electric motors should be suitable for the UK electricity supply voltage, phases and cycles and able to operate within the range of voltage variations permissible on the national grid.
Most centrifugal pumps cavitate but some may suffer cavitation damage if incorrectly installed or if the pump is incorrectly used. This may seriously damage the pump impeller and result in poor pump performance.
Their power consumption should be considered taking account of the efficiencies of both pump and motor. The efficiency of the pump and the efficiency and power factor of the motor should be as high as possible for the duty range required.
Cavitation may occur when the flow from the pump is greater than the design flow.
The type of electric motor used will depend upon the type of pump that is to be driven. For most pumps, excluding submersible pumps, a totally enclosed fan ventilated motor should be adequate to meet the requirements of the typical operating conditions in which an irrigation pump would be working in the UK.
If the suction lift becomes too great, the NPSHR could exceed NPSHA, with resulting risk of cavitation. If a pump is cavitating it tends to be noisy with a continuous crackling sound. There may also be excessive vibration. 10.4.2 Borehole pumps Borehole pumps are a form of centrifugal type pump specially adapted for use in boreholes. They may be driven either by a power unit mounted at ground level (shaft drive) or by a power unit fitted underneath the pump itself and installed within the well (submersible motor driven). For shaft driven pumps the diameter of the pump, length of fittings and borehole straightness should be correct for the installation of the pump unit in the borehole. The diameter of the borehole and its straightness may limit the size of pump that can be used and hence the yield from the borehole.
For submersible pumps, a special submersible motor will be required. Usually the pump and the motor are supplied as an integral unit by the manufacturer. Alternative motor enclosure types are available to suit the different conditions under which the motor may be operating, especially if outside or in a pumphouse. These include drip proof and totally enclosed fan cooled. The temperature motor rating is dependent on the type of insulation used in the windings. The correct rating should be applied. Various types of enclosure protection to different IP specifications (see BS EN 60529) are available. IP 54 and IP 55 specifications should be suitable for most irrigation applications. IP 65 may be used on certain motor installations.
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Additional matters that may require consideration for motors include provision of heaters, protection, motor derating, speed, slip and service factor. The manufacturer should be consulted for the correct specification for the application. The starter selected for operation with the electric motor should be compatible and may need to incorporate protection equipment and other features as required. Single-phase electric motors normally use direct on-line starters. Three-phase electric motors may use either direct on-line starters, star delta starters, auto-transformer starters or other suitable types of starter. Each starter type has its own particular performance characteristics for torque and current. The starting torque and current vary greatly between the various types of starters available. Direct on-line starters are usually only suitable for smaller motors. The general build of the starter should prevent entry of moisture, dust etc., while mounting supports should be adequate. Facilities incorporated within the starter may include isolator, overloads, protection circuits, meters. The starter specification should be made in conjunction with the electric motor. 10.5.3 Internal combustion engines Only diesel internal combustion engines are considered here, as these are the type of engine most commonly installed on irrigation schemes in the UK. They offer the advantages of fuel economy and good power output, characteristics which are very suitable for the requirements of irrigation pumping. Small diesel engines (having one or two cylinders) are usually hand started, have no protection facilities for either the engine or the pump and have no electrics. Engine accessories will cause additional loads on the engine. These may include radiator fans, alternators, oil coolers. An allowance of up to 10 % should be made for these losses. An air cleaner configuration which comprises a pre-cleaner and a filter element should be suitable for most applications. If the pump is a portable unit, a fuel tank may be fitted to the pump set, otherwise a separate fuel storage tank may be used. The type of exhaust system and configuration depends on whether the pump unit is mobile or installed permanently. Starting of the engine may be by battery or mechanical start depending on the site conditions and requirements.
Engine and pump protection may be fitted to the engine to protect against engine overheating and low oil and no water in the pump. It is essential that the engine power available at the various duty points required by the pump is carefully matched to ensure that performance over the duty range can be achieved. When selecting and specifying the engine size a n allowance of about 10 % should be made to allow for wear and tear in the engine. The engine speed should be matched to the speed of the pump to give optimum performance at the duty point or duty range. The gross power requirements for a diesel engine pump unit should include the power absorbed by the pump, the losses incurred through the gear drive attached to the pump, derating factors, engine accessories and service factor. 10.5.4 Power-take-off shaft power Power from the power-take-off (PTO) shaft on a tractor may be used to drive an irrigation pump. The power available at a tractor PTO should be checked with the tractor manufacturer to ensure that the power required by the pump can be met by the PTO shaft. The power available at the PTO is at least 10 % less than the power available at the engine and is specified at the speed for the PTO shaft, usually 540 rpm or 1 000 rpm. The safety guards that protect persons from the PTO shaft should be properly fitted. The actual maximum angle of deviation of the PTO shaft and the actual maximum PTO speed should be checked against that specified to ensure that the PTO shaft does not fall at the couplings due to excessive angle of operation or excessive velocity. The pump may be connected to the power unit via either a three-point linkage or a trolley assembly. Engine protection equipment should be considered for installation on the tractor to provide protection for both the engine and the pump. 10.6 Power transmission Power can be transmitted from a power unit to a pump via either a direct coupling, a flexible coupling, various belt configurations, or a gear drive. The pump may be directly coupled to the motor on both electric motor drives and diesel engine drives, thus providing a short close coupling between the power unit and the pump. A flexible coupling may be used where a pump unit and a power unit are separated. The flexible coupling is usually mounted on a base plate and provides easier coupling and alignment.
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BS 7562-5:1993
V belts, if correctly set up and sized with the power to be transmitted, may be suitable for connection between the power unit and the pump. Losses incurred should be low. Gear drives, such as those used for engine driven shaft drive borehole pumps, should only incur low losses in the gearbox. 10.7 Control and protection equipment The functions of the control and protection equipment are to provide control for starting and stopping the pumpset and to provide protection for both the pump and the power unit. Starting equipment should be suitable for the power unit with which it is required to operate. The equipment should have the facilities to incorporate protection when and where necessary. Pump protection equipment usually takes the form of protecting the pump against low or high pressure and against poor discharge resulting from low suction water levels or a depriming of the pump. An electric motor may be protected against overload, overheating, over and under voltage, phase imbalance, phase failure, low or high current, etc. The specific requirements should be considered in relation to reliability, cost etc.
Before the performance can be tested, the priming should be checked to make sure that the pump can be adequately and correctly primed before the motor is started. If there is a bleed valve on top of the pump, this should be opened to provide a physical method for checking that the pump unit is adequately primed. The pump discharge at the duty point should be measured using either a flow meter or flow test using one of the methods described in Part 3 4) of this British Standard. The operating pressure of the pump unit at the duty point should be checked by reading the pressure gauge fitted to the delivery side of the pump unit. The pressure reading should be taken in conjunction with the flow rate to make sure that the correct duty point on the pump characteristic curve is being studied. The vacuum gauge on the suction side of the pump unit should be read to check that the vacuum being produced by the pump is correct and conforms to the design data. The speed of rotation of the pump unit at the duty point should be checked to make sure that the flow and pressure produced are being achieved at the correct speed.
An engine may be protected against overload, excessive speed, overheating and low oil pressure. The commonest protection facilities for the engine are overheating of the engine and low oil pressure.
When the pump unit is running at normal operating conditions, it should be checked for vibration to make sure that neither the pump unit nor the power unit are vibrating excessively.
Both engine driven pump units and electric driven pump units can be automated if and when required. The degree of automation depends upon the supervision requirement at site and general requirements.
Pump bearings and glands should be checked for any overheating. Glands of the packed-gland type should be dripping at the rate recommended by the manufacturer.
Automatic stopping of the pump set is a normal feature, where engine protection units are fitted. This may be achieved by the use of a timer which is preset to close the engine down at a predetermined time. Alternatively the engine may also be closed down by the use of a pressure switch. Automatic starting and stopping of electric motors may be achieved using timers, pressure sensors, water level controls or other devices which link in with the starter gear and start the unit. It is essential with any automatic starting system that the pump unit is able to perform correctly and be fully primed ready to operate. 10.8 Pump performance after installation Once a pumpset is installed and ready to be operated it is advisable to check its performance to ensure that it is operating in the manner for which it was designed. 4)
The pump suction should be checked very carefully for air entering any of the joints or through any of the fittings. The easiest way to check for leaks is by applying a soap solution or similar liquid to the suspected leak points. Leaks on the discharge fittings should be checked especially to see if water is leaking out under pressure from any of the joints of fittings. Any unusual noises should be checked, located and investigated to ensure that they do not indicate a fault with the pumpset. The current consumption (electric motors only) should be checked against the ammeter fitted to the starter panel. The reading taken should be checked against the voltage of the electrical supply to establish that the supply is correct.
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In preparation.
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BS 7562-5:1993
It may be possible to check the fuel consumption of internal combustion engines and compare with the specified fuel consumption figures. The operating procedures for the pumpset as given in the instruction manual should be followed. These instructions should include complete closing of delivery valves prior to priming of the pump unit and slow opening of delivery valves. The procedures should be checked to make sure that they are in the correct order and that no instructions have been omitted. The shut down procedures for the pump unit should also be checked to make sure that they are correct. Protection systems supplied for the pump unit should be checked very carefully.
11 Applying chemicals Agricultural chemicals can be applied to crops by injecting them into the water in the irrigation system. Fertilizers, herbicides, insecticides and fungicides may all be applied through the irrigation system. Any person wishing to investigate the application of chemicals should consult the appropriate authorities for clarification of the situation in their area with regard to regulations applicable to this practice. ` ` , , ` ` ` , , , ` ` , ` ` ` , ` ` , ` ` ` ` ` ` , ` ` , ` ` , , ` , , ` , ` , , ` -
12 Safety 12.1 Introduction Safety in the operation of the irrigation equipment should be considered at all times to be of great importance. Safety for both persons and equipment should be considered for all types of equipment being used. General safety recommendations in the use of equipment also apply to irrigation equipment. The Health and Safety at Work etc. Act [1] lays down guidelines to be followed. 12.2 Pumping equipment Pumping equipment can present many hazards, including rotating parts, high pressures, high temperatures, electrical shocks, fuel and chemicals. All of these can be a risk to the operator and persons involved should be made fully aware of the dangers. All equipment should be correctly guarded so that risk to operators or others is reduced to the minimum. All equipment should be correctly maintained to ensure that dangerous failures cannot occur or built-in protection facilities do not fail.
12.3 Supply mains Piping used in either above or below ground mains can present potential hazards to persons. These hazards include high pressures, pipe bursts, valve blow outs. Other hazards occur when the equipment is being moved, especially long lengths of pipe, which provide a very great danger when manoeuvred near overhead power lines. Pipes used on supply mains above ground may be up to 9 m long and if raised vertically could easily strike overhead power lines. These pipes should always be moved in a horizontal position, as near the ground as possible. The pipes should not be left a nywhere where the public might gain access. 12.4 In-field equipment In-field equipment may present particular hazards caused by, for example, rotating parts, high temperature, electricity, high pressures. All equipment should be correctly guarded so that risk to operators or others is reduced to the minimum. Accidents, including fatalities, have occurred when machines have been used too close to overhead power lines. Common causes include ignoring self clearance, mechanical failures, contact during transportation and careless handling of piping. Conductor clashing resulting in loss of supply has been caused by the impact of water j ets on overhead power lines. The electricity authority should be consulted at the design stage of the irrigation system and at installation to ensure that all precautions are taken. Rainguns, often fitted to self-travellers, potentially may cause a hazard by either passage of current or clashing of conductors. Passage of current may occur where a full stream water jet acts as a conductor from the power line to the irrigation equipment. Clashing of cables may occur where the jet of water hits the cable at such a force that the cables meet. The use of ring nozzles helps to break up the water jet, but at the same time reduces the radius of throw of the raingun. It is preferable for the raingun fitted to a self-traveller to run parallel to the power line and not underneath it. The recommended minimum distance that the gun should operate from the power line is 30 m. The electricity authority should be consulted for their advice. The hosedrum unit height should also be considered with respect to the height clearance between the top of the machine and the minimum sag level of the power line. Special care should be taken where the power line passes across a slope in the field, as the minimum sag level of the power line may be nearer to the ground.
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BS 7562-5:1993
Boom irrigators may present two hazards: height, and horizontal distance. The height of the machine when the booms are raised may be 6 m or 9 m above the ground. This type of machine should not be driven under power lines unless the booms can be kept in the lowered position. The minimum distance between the boom and power lines should be 15 m from the tip of the boom. This distance recommendation may alter depending on the type of boom used, that is whether it rotates while irrigating or moves while irrigating. Ground slopes over which the boom travels may have a particularly dangerous effect on the reaction of the boom to the ground undulation, in the vicinity of power lines. Gateways are a common problem area where uneven or sloping ground may exist. The booms, when being moved, should be anchored at each end to prevent rotation.
Centre pivots, being located in one position and rotating about that position, should not present a problem once correctly installed. Linear moves, due to their moving while irrigating, should be designed after studying the area to be irrigated to avoid any potential dangers. Protection equipment should prevent the machine from coming closer than the recommended distance to hazards. If contact is made between the equipment and a live power line, no one should approach the equipment. The electricity authority should be advised immediately. Warning notices should be fitted to all equipment where a risk could occur. Operators should be made fully aware of the dangers of operating near power lines and the potential dangers the equipment presents.
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BS 7562-5:1993
List of references
(see clause 2)
Informative references BSI standards publications BRITISH STANDARDS INSTITUTION, London
BS 7459, Rotating sprinklers for irrigation equipment. BS 7459-1:1991, Specification for design and operational requirements. BS 7459-2:1991, Methods of test for uniformity of distribution. BS 8010, Code of practice for pipelines. BS 8010-1:1989, Pipelines on land: general. BS EN 60529:1991, Specification for degrees of protection provided by enclosures (IP Code). ISO publication INTERNATIONAL ORGANIZATION FOR STANDARDIZATION (ISO) ,
Geneva. (All publications are available
from BSI Sales.) ISO 9260:1991, Agricultural irrigation equipment — Emitters — Specification and test methods. Other references [1] GREAT BRITAIN. Health and Safety at Work etc. Act 1974. London: HMSO.
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© BSI 07-1999
Copyright British Standards Institution Provided by IHS under license with BSI - Uncontrolled Copy No reproduction or networking permitted without license from IHS
Licensee=AECOM EW & Canada/5906698006, User=Zaraket, Ahmad Not for Resale, 01/16/2016 04:55:36 MST
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