The Cla-Val 50-05 Pressure Relief, Air Release and Vacuum Breaker Valve is used to prevent surges during deep well pump start; and vacuum formation during pump shut-down operations. The valve is in the open position when the pump is started, discharging all of the air in the pump column and piping to the atmosphere. As the water begins to flow through the valve, the air release valve senses the change and closes, causing the main valve to close slowly through an adjustable restriction.