2.4.3 Storage Tanks and Reservoirs:
Storage tanks and reservoirs are used to provide storage capacity to meet fluctuations in demand (or shave off peaks), to provide reserve supply for fire-fighting use and emergency needs, to stabilize pressures in the distribution system, to increase operating convenience and provide flexibility in pumping, to provide water during source or pump failures, and to blend different water sources.
2.4.4 Valves:
The two types of valves generally utilized in a water distribution are isolation valves (or stop or shutoff valves) and control valves. Isolation valves (typically either gate valves or butterfly valves) are used to isolate sections for maintenance and repair and are located so that the areas isolated will cause a minimum of inconvenience to other service areas (Bhole).
Maintenance of the valves is one of the major activities carried out by a utility. Many utilities have a regular valve- turning program in which a percentage of the valves are opened and closed on a regular basis. It is desirable to turn each valve in the system at least once per year.
The implementation of such a program ensures that water can be shut off or diverted when needed, especially during an emergency, and that valves have not been inadvertently closed. Control valves are used to control the flow or pressure in a distribution system (Twart,1995). They are normally sized based on the desired maximum and minimum flow rates, the upstream and downstream pressure differentials, and the flow velocities. Typical types of control valves include pressure-reducing, pressure sustaining, and pressure-relief valves; flow-control valves; throttling valves; float valves; and check valves.
2.4.5 Hydrants:
Hydrants are primarily part of the firefighting aspect of a water system. Proper design, spacing, and maintenance are needed to insure an adequate flow to satisfy fire-fighting requirements of American Water Works Association-M-31(1989).
2.5.0 VALVES AND FITTINGS:
Valves are required to control the flow of water, to regulate the pressure to release or to admit air and to prevent flow of water in opposite direction (Balint, et al.2002). In every noses various types of fittings such as taps, bends, tees, sockets etc. are required for the distribution and forming network of the pipes inside the noses standard specifications for most commonly used valves are published by British standard institution.
