Pressure and Hydro-Pneumatic Tanks

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Pressure and Hydro-Pneumatic Tanks

Hydro-pneumatic tanks are designed to store water and air under pressure. With stored air pressure, this type of water storage does not require the constant use of a pump, saving energy and wear and tear on the pump, while quickly providing water on demand. Separated by a diaphragm, the 30 to 50 psi system is pre-charged (pre-pressurized) to 25 psi in the air portion and should be 2 psi below the pump start-up pressure.

The system has four operating cycles based on pressure. The start-up cycle occurs when the pressure is 28 psig and the diaphragm is pressed against the bottom of the air chamber. In the fill cycle, water is pumped into the tank’s reservoir forcing the diaphragm upward into the air chamber, exceeding 40 psig. A pressure of 50 psig initiates the hold cycle shutting off the pump. At this point, the diaphragm is at its highest position and the water reservoir is filled to capacity. During the delivery cycle, the pump stays off (until 40 psig is reached) while pressure in the air chamber forces the diaphragm downward to deliver water with a system pressure of 40 to 50 psig.

For safe operation, a maximum 100 psig is specified for some models.

A O Smith Hydro-pneumatic Well Tank

Image source: A O Smith at Lowes

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