The air  vessel  shall be provided to compensate for slight loss of pressure in the system and to provide an air cushion for counter-acting pressure, surges, whenever the pumping sets come into operation.

Air vessel shall conform to IS: 3844.

It shall be normally half full of water, when the system is in normal operation. Air vessel shall be fabricated with M.S. plate with dished ends and suitable supporting legs. It shall be provided with one flanged connection from pump, one drain with valve, one water level gauge and sockets for pressure switches. The air vessel shall be tested to pressure for 12 hours at 2 times the operating pressure or 1.5 times the shut-off.