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Pressure in Water Supply Systems for Buildings
The pressure in water supply systems must be regulated and maintained within a certain range for both safety as well as usability requirements. Water pressure in high rise buildings is primarily affected by pumps and gravity itself. Pumps are used to transfer water from the underground main supply to a holding tank that is typically located in either the roof or within intermediate levels of the building. The holding tanks would feed water to the lower floors with the help of pressure induced by gravity. Once empty, the pump would subsequently be activated to refill the tank.
Gravity feeding and pumps in the water supply system can lead to water pressures outside the acceptable range, causing potential damage such as leaks or even pipe bursts. Hence, there is a need to regulate the pressure using pressure reducing valves or pressure relief valves.
Pressure Reducing Valve
A pressure reducing valve’s key function is to maintain a predetermined downstream pressure regardless of fluctuations from the upstream pressure. It operates by closing the valve to an extend in response to the detected downstream pressure, with the valve completely closing when downstream pressure reaches the set value. The pressure reducing valve is suitable for systems that demand certain downstream pressure, such as maintaining pressure for fittings that we use (e.g., taps and urinals). Since the pressure of a gravity-fed system increases with the vertical distance from the water tank, having fittings of pressure reducing valves at regular intervals would enable pressure to be maintained within the acceptable range throughout the system.
Pressure Relief Valve
The pressure relief valve’s key difference from the pressure reducing valve is the regulation of upstream pressure as opposed to downstream pressure. After setting the predetermined pressure, any excess pressure from upstream would cause the valve to be opened proportionally in response, allowing water to flow to an auxiliary pipe. This would relieve the excess pressure and maintain the pressure of the system below the settings. The pressure relief valve is mainly used to protect equipment and fittings from overpressure in the system caused by pumps. In the event of sudden decrease in water demand in the system, a pressure relief valve would allow the system to maintain acceptable pressure even when the pump continues to operate without adjustment.
Sizing the Control Valves
For control valves to work effectively, it is not recommended to size the valves by just the pipe size as there might be specifications that differ for control valves as opposed to regular pipe fittings. Instead, it would be best to size the valves in accordance with the amount of flow and pressure they would receive. Incorrectly sized control valves will cause numerous issues that will impact the lifespan of not just the control valves, but also other components in the water supply system. Additional considerations must also be made due to phenomena that can cause surges in pressure, such as water hammering. Thus, it is always recommended to have an expert opinion on the placement and sizing of control valves to best optimize the water supply system.
For more information and consultation regarding the sizing and placement of control valves, do email us at
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1: PUB – Handbook on Application for Water Supply