Chapter II - Review of Related Literature

CHAPTER II - REVIEW OF RELATED LITERATURE

2.1 Water Distribution System The essence of water distribution system is to supply adequate amount of water of safe quality under sufficient pressure to meet the demands of a certain community or a building. So, in the design and analysis of a water distribution system the quality and quantity of water available and the pressure and rate of use must be considered and also determine the problems that may occur in constructing or operating of the actual water distribution system.

2.1.1 Gravity Pressure System The gravity pressure system is possible only when the source of supply is located substantially above the level of the demand community. This is the most dependable method, provided that there are multiple-protected pipelines carrying the flow (Mc Ghee, 1991). This system is inherently associated with elevated storage or tank. The storage facility provides the reservoir in which the inflow and outflow of water can better match the hourly consumer demand and act as a supply source during emergency situations. Elevated storage are located within or adjacent to areas of high demand of the distribution grid to meet water demands in those areas without causing high velocities and head losses in the distribution mains. Also, booster pumps may be required if the pressure in the gravity system supplying the storage facility is not enough to fill the reservoir. There are two types of tanks that are commonly used in a gravity pressure system: a.) Elevated Steel Tank – are usually considered when the surrounding terrains are relatively uniform. Elevated steel tanks are manufactured in a variety of ellipsoidal and spherical shapes with capacities ranging from 200 to 12, 000 m3 (Hammer, 1986). The height of the tank will be determined based from the topography of the area served, the height of the buildings and the pressure losses in the distribution system. Altitude valves, check valves and shut off valves are necessary to control the level of water in the tank and to provision or isolate portions of the distribution system during emergencies (USCE, 1986).

b.) Ground level storage – are considered when the difference in the elevation of the supply facility and the area of demand is sufficient to provide adequate pressure in the distribution system. Steel standpipes are usually available in sizes up to 20,000m3(Hammer, 1986). Concrete reservoirs can be used in any size system, but are more often used for larger sizes (USCE, 1986).

2.1.2 Direct-Pressure System The direct pressure method is used when there was no elevated storage provided, and the required pressures are maintained only by the pumping facilities. Direct pressure system can be categorized in two methods: a.) pumping without storage and b.) pumping with storage (Mc Ghee, 1991). a.) Pumping without storage- is the least desirable method of direct pressure system since it provides no reserve flow in the event of power failure and pressures will fluctuate substantially with variations of flow. Sophisticated controls system is required to handle constant varying of flow to match unpredictable demand. b.) Pumping with storage- a ground level storage tank may be provided to serve as an intake supply for the pumping facilities. In this method, water is being pumped at a more or less uniform rate, with flow in excess of consumption being stored in elevated storage tanks distributed throughout the system. In direct pressure system, caution must be used in the design to reduce surge pressure and compensate for variable volume demands. The pumping facilities in a direct pressure system must have firm capacities equal to or greater than the peak demand rates exerted on the system (USCE, 1986).

2.1.3 Pneumatic System Pneumatic distribution systems are applicable where demands for water supply are less than 2 m 3 per minute. The system has a low pressure setting with minimum operating pressure of 30psi and a high pressure setting that is dependent on the max allowable pressure in the distribution system.

Pneumatic pressure is air pressure over and above atmospheric pressure. It is the pressure which is registered on the pressure gauge and which makes water flow from hydropneumatic tank (Wright, 1956). The hydropneumatic tank “riding” on the system functions in two ways (USCE, 1986). 1.) In case of emergency, the hydropneumatic tank can act as a supply for a short period of time 2.) In can act as an air spring or piston and is a reservoir of stored energy to maintain pressure in the system and help avoid short-cycling of the pumps.

2.1.4 Water Supply in Buildings Water enters the building through service pipe and terminates just inside the building. From the water main, should stored the water in an underground reservoir or should then branch into risers, intermediate pipes, and pipes in individual fixtures. Two systems of water supply piping can be used depending on which piping is much appropriate for the building, hydropneumatic system and gravity pressure system, but sometimes dual water supply systems or the combination of the two is installed (Babbit. 1950).

2.2 Household Water Supply Water

is

a

prime

necessity in all types of households. It conveyed from the main to the

Figure 2.1 Hydropneumatic System

Figure 2.2 Gravity Pressure System

household or buildings by means of pipes classified as: 1.) House Service, 2.) Riser and 3.) Branches (Fajardo Jr. 2001). House service refers to the pipe connection from the public water main or any source of water supply to the building served. Riser refers to the vertical supply pipe which extends upward from one floor to the next. Branches are horizontal pipes that serve the faucets or fixtures.

2.2.1 Pipe Material Different pipe materials can be used for water distribution depending on the need and environment where it will be installed, but more importantly a water distribution pipe must have the following characteristics: adequate tensile and bending strength to withstand external loads; high bursting strength to withstand internal pressure; smooth and non-corrosive interior surface for minimum resistance to flow; ability to convey hot water (Hammer, 1986). In the National Plumbing Code Handbook (2005) cite several kinds of pipe material and their common uses are cited. Copper pipes are the most common type of pipe for potable water system. Copper tubing is the most expensive material but it is noncorrosive to most waters. Two types of copper tubing is available the hard-drawn tubing and the soft tubing. Hard drawn tubing is commonly installed before the finish is put on; in the contrary the soft copper tubing is used extensively where it must be “finished” through partitions, ceilings and floors. Copper tubing or pipe is durable and is approved for hot and cold water. The pipe is rigid; it can be installed to allow the draining of the water system. There three standard grade for copper pipes, type L, is use for indoor plumbing where pressure is moderate, type K the heavy duty grade and type M, which is used above and below ground (Wright, 1956). Brass Pipes are suitable for water distribution, but it is not normally used in modern applications. It was replaced by new materials that are easier to work with and which provides longer services. Galvanized Steel Pipes are used particularly in circumstances where diameter is large and pressures are high. It has economic advantage due to its strength and lightweight. Steel Pipes

compared to iron pipes is cheaper, but it is difficult to work with and is subject to rust-related problems and more likely to be structurally damage by corrosion than iron. Cast Iron Pipes are used primarily for underground water supply, but is seldomly used for supply in buildings. It is sometimes called as ductile pipe and used in large water mains. Chlorinated Polyvinyl Chloride pipes are pipes that have been used for many years in water service, due to its flexibility, high tensile strength and its ease in cutting. Suitable for hot and cold water lines supply, but due to its difficulty in preparation for installation such as application of primer for its pipe and fittings and relatively low strength in connections professional plumber do not recommend these pipes nowadays. Polyethylene pipes are plastic pipes that resist chemical reactions and fairly flexible. PE can be used in great distance, without joints. Although it can be subjected to crimping in difficult turns it can last satisfactory service years, and is cheaper than other pipes. Cross-linked Polyethylene (PEX) are the most commonly used material for water distribution systems in buildings due to its low capital cost, low installation cost, less joints and less potential for leaks and corrosion ( Babbit, 1950).

2.2.3 Types of Valves Valves purpose is to control the magnitude and direction of water flow in the system. Valves can be categorized based on kind, operating purpose, and function (Hammer, 1986). Commonly Used Valves Gate valves are most commonly used for on-off service. Gate valves isolates for breaks and maintenance in different part of the system. It provides gradual shutting-off to the flow by turning the gear of the valve. It consists of a sliding, flat metal disk that is moved at right angles to the direction by a screw operating system. Common types of gate valve include double-disk, parallel-seat cast-iron valve with a non-rising stem. Butterfly valves provide tight shut-off, low head loss, small space requirements and throttling capabilities. Butterfly valves were widely used in both low and high pressure applications; the

only restriction is that it is not suitable for liquids that contain solid material which might prevent their complete closure. Ball valves have advantage of ease of operation, reliability, durability, and capability of withstanding high pressures, but are usually expensive. Globe valves are seldom used in large water distribution system, their primary application is in household plumbing where their low cost outweighs their poor hydraulics characteristics. The gasket or disk is forced down upon the seat of the valve by turning the handle, thus shutting off the flow of water. The only problem is that when leaks occur in the valve it will be difficult to stop. Small globe valves normally have rubberized discs and metal seats to provide drip-tight shut-off. Check valves are semi-automatic device that permits water in only one direction. It opens under the influence of pressure and closes automatically when flow ceases. The two basic type of check valves are lift check and swing check. a.) lift check valve has a flat that moves vertically within the valve body, opening with vertical flow and closing by gravity or spring actions when flow stop. b.) swing check valve has a closed disk that rest at right angles to the direction of flow and where the disk that can be lifted to provide full flow. Pressure Reducing valves are automatic valves operated by pilots to maintain a preset outlet pressure against a higher inlet pressure. Common application of PRVs is installation in a main connecting to a separate pipe network located on two different elevations. Preferred location of the PRV is adjacent to, and upstream from, the water supply that has adversely affected by excessive pressure. Pressure Relief valves or Safety valves are used to prevent dangerously high pressure in plumbing supply and for many other purposes. They are essential on hot-water supply systems to control for the expansion of water or the possible generation of steam. (Hammer, 1986)

2.2.3 Joints and Connections

A joint is required each time it is necessary for piping to be connected either to itself, to fittings or to a piece of equipment. It must be able to withstand the pressure induced by the system. Joints may be attached in many ways such as welded or threaded (Matamorosa, 2004). Fittings are used to connect pipe to one another and to change the direction of straight run of flows. In choosing fittings material, put into consideration the type of pipe to be used. For steel and wrought iron pipe, fittings are threaded and made of malleable iron and cast iron. For plastic, copper, and brass pipes, fittings are made of same material as the pipe being connected. A variety of fittings can be used to manipulate the runs, 45˚ and 90˚ for changing the direction of the flow. Unions and couplings are used to join straight runs for pipe. Tees are used to provide branching of low. Reducers and enlargers are used to when there are change in the diameter of pipe. Adapters are used where threaded pipe is being connected to copper or plastic. Plugs and caps are used to end the flow in pipe (Dagostino, 1995).

2.2.4 Types of Pumps Pumps are used to displace fluid such as gas and liquid. A pump can move fluid through physical or mechanical. Pumps that is commonly used in small water supply includes (1) single stroke suction lift pumps; (2) single acting and double acting suction-lift and force pumps; (3) rotary pumps; (4) reciprocating, turbine, air lift, and deep-well jet pumps; and (5) centrifugal pumps (Babbit, 1950). For this study some related pump type are defined: Centrifugal Pumps use a rotating impeller to increase the pressure and flow rate of a fluid. They are the most common type of pump used to move liquids through a piping system. The fluid enters the pump impeller along or near to the rotating axis and is accelerated by the impeller, flowing radially outward or axially into a diffuser or chamber, from where it exits into the downstream piping system. These pumps are usually used in large discharge. Booster Pumps are used when the pressure on the system is not enough. Booster pumps add total head on the system so that water can flow to the whole system.

Submersible pumps had advantage in terms of space, since it can be drowned into water. Through suctions, water is lifted from the storage tanks to risers, which delivers water to discharge. It is commonly used in buildings with centralized water supply and sewage treatment facilities.

2.2.5 Pressures, Energy, Heads and Losses Pressure is the amount of force acting on a unit area. In fluids where density remains constant, pressure on the unit area depends on the height, or depth of the water. A formula develops: Pressure=Weight x Height

Fundamental law in hydraulics states that “the pressure at any one point in a static liquid is exerted with equal intensity in all direction.” Pressure is expressed in terms of pounds per square inch (psi) or in Pascal (Pa). Pressure can be measured by a piezometer or a pressure gage. A piezometer is a narrow, open ended vertical tube, attached at the point of pressure measurement. Water will rise in the tube to a height equivalent to the pressure. Pressure gage is a compact, practical device used for pressure measurement. It is usually attached directly onto the pipe, reads pressure directly from it. An example of a pressure gage is a Bourdon Tube. Energy exists in two kinds, kinetic and potential. In a water system, kinetic energy is demonstrated by the velocity of the fluid. Potential energy is present as elevation of the fluid above a reference point, or as pressure. The summation of these three possible energies in a water system is expressed in an equation known as Bernoulli’s Equation, which is the basis for all hydraulic calculations. Bernoulli’s Equation for the total energy at point 1 to point 2 is expressed as: P1γ+v122g+z1 =P2γ+v222g+z2 +HL

Where: P1 = Pressure at any point 1in the system. v1 = velocity at any point 1in the system z1 = elevation of point 1 P2 = Pressure at any point 2in the system. v2 = velocity at any point 2in the system z2 = elevation of point 2

γ = specific gravity of the fluid g = acceleration due to gravity

As shown in the Bernoulli’s equation, there are three types of heads; pressure head, velocity head and elevation head. Pressure head is the pressure which directly due to the depth of the water. For a dynamic system pressure will decrease over the length of the pipeline due to friction losses in the pipe. Velocity head is the distance which the water can move due to velocity energy. In a pressurized pipe system, velocity head is usually the smallest of the three energy components. Elevation head is measured from a point of reference, or Datum, to the bottom of the water or to the surface of water (Hauser, 1996). Head loss in dynamic system is the pressure decrease along a length of the pipeline due to friction. Major Head loss accounts for most of the pressure drop in the dynamic water systems. Minor head loss is due by turbulence created at bends, fittings, and diameter changes in the pipeline, the lesser component of pressure loss. Components of Head Loss

1.) Roughness – dependent upon pipe material, the roughness of the interior surface of a pipe. Turbulence in normal flow increases with pipe roughness thus more energy is spent, and pressure drops over length. 2.) Length – losses occur with every foot of pipe length, the longer the pipe the greater the loss. 3.) Diameter – the larger the diameter, the less of the water will touch the surface of the pipe that encounter friction, therefore the lesser the loss than smaller diameter. 4.) Velocity – the faster the flow in the pipe, the more turbulence is created, and the more head loss will occur.

From these components a formula was developed, the Darcy-Weisbach Equation (Cabaltica, 2009):

HLf=fLv22g

where: HLf = Friction head loss f

= friction factor

v = velocity g = acceleration due to gravity

From this equation, Hazen and Williams derived the more easily usable formula the HazenWilliams formula (Cabaltica, 2009).

HLf=10.67 LQ1.85C1.85D4.87for SI Unit

HLf=10.67 LQ1.85C1.85D4.87for English Unit

where: HLf = Friction head loss L = pipe length Q = discharge C = Hazen-Williams coefficient

Minor head losses are caused by changes in the momentum of flow due to: a.) change in the cross-section of flow path, b.) change in the flow direction and c.) the presence of obstruction in the flow path such as valves and fittings (Cabaltica, 2009). hm=Kv22g

Where: hm = minor head loss K = head loss coefficient v

= velocity

g = acceleration due to gravity

2.3 Distribution System Pressure Problems In water distribution in the building unnecessary or unpredictable events may happen that can be cause failure or inefficiency of the system. These problems may be due to the pressures running on the system, large variation of pressures will be alarming. In designing a distribution system it is necessary to know and address these problems to make the system sound and efficient.

2.3.1 Water Hammer “Water hammer is a term used to define the destructive forces, pounding noises and vibrations which develop in a piping system when column of non-compressive liquid is flowing through a pipeline at a given pressure and velocity is stopped abruptly.” The phenomenon can cause silent but rapid fluctuations of pressure that may set up vibrations in the conduit and its supports resulting in alarming noises, bursting of the conduit, or other damages (Babbit, 1950). “A less severe form of hammer is called surge, a slow motion of mass oscillation of water caused by internal pressure fluctuations in the system (Lahlou, 2003).” Both water hammer and surge are referred to as transient pressures. If not controlled, they both yield same results: damage to pipes, fittings, and valves, causing leaks and shortening the life of the system. Neither the pipe nor the water will compress to absorb the shock.

2.3.2 Cavitation Cavitation is a complex phenomenon that may take place in pumps. If the pressure falls below the vapor pressure corresponding to the temperature of the liquid, pockets of vapor form. When the vapor pockets in the flowing liquid reach a region of higher pressure, the pockets will collapse with a hammer effect causing noise and vibration. Severe cavitation can result in reduced efficiency and ultimate failure of pump and other equipment.

2.4 Softwares Used for Water Distribution Analysis Since analyzing of a complex water distribution would be very tedious and would a lot of brains and time, engineers and designers used several programs to analyze a system. These programs or softwares become very useful and handy in terms of evaluation, modeling and flow analysis. Many programs are created depending on what is needed and essential for engineering works.

2.4.1 EPANET “Epanet is a computer program that performs extended period simulation of hydraulic and water quality behavior within pressurized pipe networks.” (www.epa.gov/en2manual.html) EPANET, a network consists of pipes, nodes, pumps, valves and storage tanks or reservoirs follow the flow of supply of water in each pipe, tracks the pressure at each node, height of water in each tank, and the concentration of a chemical species throughout the network during a simulation. It main purpose is to help in the design for improving our understanding the movements of water in a distribution system. 2.4.1.1 Application of EPANET Epanet can be used for many kinds of application s in distribution analysis, these include the following: 1. Sampling Program Design 2. Hydraulic Model Calibration 3. Chlorine Residual Analysis 4. Consumer Exposure Assessment In addition to these applications EPANET can also assess alternative management strategies for improving water quality in the system (www.epa.gov/en2manual.html).