How To Size A Pressure tank For Your System

A properly sized pressure tank is essential if you want to increase the life expectancy of your pump or want to reduce its power consumption.

The chances of premature pump failure can be minimized to a great extent if you have the right tank. In incorrectly sized pressure tanks, there are chances of short cycling of the pump. When the pump shuts off and turns on often, then it is referred to as short cycling. Short cycling causes overheating of the pump, which can lead to pump failure. Besides that, it also increases the power consumption of your pump. Generally, larger pressure tanks are always a good option.

To bear down on the water using compressed air, water pressure is created by a pressure tank. By compressed air, water is moved out when a valve opens. Until the pressure reaches your pressure switch lower preset value, the water is pushed within the whole plumbing of the house. 

The pressure switch gives a signal to the pump to run on when the low setting is reached, and a greater amount of water is pushed into the tank.

There will be more drawdown or amount of water stored if you have a bigger tank. Due to this, there would be fewer cycles due to the greater run time. For effective cooling of the motor, at least run time should be of one minute, according to most manufacturers. A greater run time might be needed for pumps that have a horsepower of one or more.

Three points should be considered to decide the pressure tanks sizing:

·       In GPM (gallons per minute), the flow rate pump has

·       The approximate run time that you want for your pump

·       The preset low (pressure cut in) and high (pressure cut out) of the pressure switch in PSI (pounds per square inches). On the low preset pump turns on, and at the high preset pressure, pump turns off.

Then based on the values from the above points, the following formula can be used to calculate the drawdown:

Needed drawdown capacity of tank= pump flow rate * run time

Between the pumps turning on and off, the minimum amount of water, the pressure tank stores is referred to as the drawdown capacity of the tank. Remember this is not the same “tank volume” and therefore don’t mix the two.

E.g., Depending on the pressure switch’s preset low and high(cut-in and cut-out pressure) setting, the pre-charged tank with a

20-gallon water volume might have a drawdown capacity of only 5-7 gallon of tank.

If your pump flow rate is ten GPM or higher, then for each GPM that the pump offers, there should be at least a drawdown capacity of one gallon.

If you have any questions please reach out to Southern California Well Service at ‪(760) 440-8520‬.

Note: In case your system has a variable frequency drive, then the above calculation cannot be used. Then check your pump’s manual if there is any tank size suggested by the manufacturers.