The pressure relief and sustaining valve protects the pumps and pipes from damages, that may be caused by water hammer because of the rapid changes of the water flow velocity. The common causes of rapid changes in flow velocity are the start -up/shut-down of pumps, fast closure/ opening of valves, filling of drained pipe at excessive flow rates.

The valve AS- E/V-30 sustains the desirable upstream pressure, regardless the changes of the flow. In case the upstream pressure is reduced below the regulated limit, the pilot closes the valve.