API Energy surge control tank is to provide a pre-determined amount of gas (often air) and liquid (often water) at the moment a surge event occurs. The air and water volumes, normally calculated by a hydraulic study which examines the hydraulics for the whole pipe system, are chosen to mitigate the transient pressures during a surge event. When low pressures occur in the connected piping the air in the tank will expand pushing the water into the system to mitigate low pressures, when high pressures arise, the air in tank is compressed and acts like a shock absorber to reduce the magnitude of the high pressures.

If the air and water volumes in the tank are not correct at the time of the surge event then excessive high and low pressures will arise which can lead to pipe bursts or collapses.

To ensure that the air/water volumes are correct, surge tanks are often provided with a control system which will maintain the amounts of air and water at the required levels within the tank at all times when the system is operating.