Pressure Valve, Pressure Relief valve
A Pressure Valve is a relief valve and controls and maintains a preset, reduced downstream (outlet) pressure by causing the main valve to throttle and sustain the desired reduced pressure regardless of variations in demand and upstream (inlet) water pressure.
Pressure Relief Valves
The throttled position is controlled by an adjustable pilot valve operating in conjunction with an orifice (or needle valve). The pilot valve senses the downstream (outlet) pressure and reacts immediately to reposition its piston as the outlet pressure tends to increase or decrease with varying demand.
The change in throttled position of the pilot valve piston causes a change in flow of control water which in turn changes the pressure above the diaphragm of the main valve, thereby causing the diaphragm assembly of the main valve to reposition and throttle to maintain the desired, preset reduced outlet pressure.