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close this bookWater Manual for Refugee Situations (UNHCR, 1992, 160 p.)
close this folder10. Water distribution systems
View the document(introduction...)
View the documentGeneral
View the documentTypes of pipeline systems
View the documentValves and taps
View the documentOther system components
View the documentConsiderations for pipeline designs
View the documentPipeline construction

Valves and taps

6. All pipeline systems require the use of valves to control flows and pressures as well as for closing or opening a pipeline or a section of it (Fig 34). As the pipeline must always follow the terrain's topography, some valves are used for the release of air that may be trapped at high points (air valves) and to facilitate emptying and scouring the pipeline to flush out sediments that may have been deposited at low points (wash out valves). Sluice valves are fitted to the pump outlets in the case of pumped supplies, but are also installed to isolate pipeline sections during operation or maintenance activities; these valves are also known as gate valves. Non-return valves consist of a flat disk set pivoted within the pipe in such a way that it may be forced open by water flowing in one direction but also forced shut, thus impeding the flow, if water tends to flow in the opposite direction. Float valves function with the same principle; the driving force is given to the mechanism by the upwards movement of a floater or buoy, thus allowing the automatic closure of inlet pipes before tanks overflow. Other valves, such as the butterfly valves, screw plug valves or ball valves are also used for flow control tasks and are built on the principle of a plug, diaphragm or jumper which is forced into the pipe's opening, thus reducing or shutting off completely the flow; as their sealing device (gasket) wears down rather quickly, they require constant attention and periodical renewal; this may become an important maintenance problem if the valves have a frequent use; an additional disadvantage of these valves is that, due to their design, they cause considerable pressure-head losses, even when completely opened. Stopcocks, also known as water taps or faucets, used at water distribution outlets at public standposts or house connections, are normally designed in accordance with the same principles of screw plug valves. They therefore suffer from the same shortcomings related to the short working life of gaskets, thus creating a major maintenance problem, especially when distribution is carried out through public distribution standposts; these taps may be opened and closed hundreds of times during a single day; as their malfunctioning is one of the main causes of water wastage, this should be given close attention during the planning and implementation of a preventive maintenance programme. Recently, very sturdy, easy to repair and maintain self-closing taps (known as water saving taps) have been developed specifically to address these problems; their introduction in public distribution standposts at refugee camps has proven successful in minimizing water wastage and camp maintenance costs.

Fig. 34a Type of Valves: gate valve

Fig. 34b Type of Valves: plug valves

Fig. 34c Type of Valves: water-saving tap