Wikipedia
A surge tank (or surge drum) is a standpipe or storage reservoir at the downstream end of a closed aqueduct, feeder, dam, barrage pipe to absorb sudden rises of pressure, as well as to quickly provide extra water during a brief drop in pressure.
In mining technology, ore pulp pumps use a relatively small surge tank to maintain a steady loading on the pump.
For hydroelectric power uses, a surge tank is an additional storage space or reservoir fitted between the main storage reservoir and the power house (as close to the power house as possible). Surge tanks are usually provided in high or medium- head plants when there is a considerable distance between the water source and the power unit, necessitating a long penstock. The main functions of the surge tank are: 1. When the load decreases, the water moves backwards and gets stored in it. 2. When the load increases, additional supply of water will be provided by surge tank.
In short, the surge tank mitigates pressure variations due to rapid changes in velocity of water.
Usage examples of "surge tank".
An hour later Khor, Eratosthenes, and Ne-tiy had wound the last of the linen strips around the hydraulic tubes, refilled the depleted oil surge tank, and secured the amphora of natron in the storage locker.