Hydropneumatic tanks are pressure vessels that hold water and air under pressure. In order to provide efficient water supply, hydropneumatic tanks regulate system pressures to quickly meet system demand. The compressed air creates a cushion that can absorb or apply pressure as needed. Air that is reabsorbed into the system water is sometimes replenished with the addition of a small air compressor. Large hydropneumatic tanks with volumes of 2,000 gallons or more are usually installed horizontally. Normal operating pressure is in the range of 60 to 75 psi., so most hydropneumatic tanks are rated to 100 psi.

A hydropneumatic tank can perform several different functions. In a booster pump application, it can provide water to the system during periods of a no flow shutdown of the booster pump or it can provide water to replace leak loads. In a well water application, it can provide the desired volume of water required between the pump shut down pressure and the pump turn on pressure.

In a sprinkler or irrigation pump application, the tank may provide a cushion to maintain necessary pressure so the jockey pump will not short cycle. In any case, the amount of water that the tank will be required to supply to the system during any given cycle is called the drawdown. Drawdown must first be determined to properly size the hydropneumatic tank.

When used as Shock and Surge Tanks, hydropneumatic tanks are used as water systems, to effectively control water hammer shock, and pump start-up/shot-down water surge. The vessels are fabricated to 250 PSI with large water system connection designed to accept potentially harmful water surge pressures quickly, with minimal pressure drop.