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Facility Management

How Constant-pressure and Gravity-fed Water Supply Systems Work

Constant pressure tank systems use a pump to give a constant water supply throughout a building. In these systems, water goes into a storage tank (known as a suction tank), from which pumps draw their supply. For instance, when an individual uses a faucet, the water will refill the faucet using the pressure from the pump. The pumps should meet the demand of the water peak load at the right pressure. Besides, they should withstand continuous or semicontinuous operation.

On the other hand, gravity-fed water supply systems have tanks placed on top and/or the intermediate floors of buildings. Water goes up the buildings and into the tank using pumps. When an individual uses water in the house, the water flows down from the tank using the force of gravity. The use of the pump is only to refill the tank after a floater valve indicates that there is a low water level. Thus, gravity-fed water supply systems provide constant water supply without the need of large and powerful pumps.

There are various issues concerning the correct application of the two water supply systems. Constant pressure tank systems require pumps that give enough pressure to counter the head and friction resistances. Thus, they require large horsepower motors that consume high amounts of energy. In addition, the tanks require periodic sediment removal as accumulated sediments might block the pumps as well as cause traces of impurities in the water. This system works well for low-rise buildings that use relatively low amounts of water.

In the case of gravity-fed systems, they require tall buildings in order to provide the correct pressure. The supply capacity should meet the average hourly flow and allow for water storage during times of low water use. Besides, booster pumps can be used to fill the tank in case of low pressure to support the supply.