Pilot Operated Safety Valve Working Principle
In the normal closed postion, system pressure is transmitted through the pilot valve and into the dome of main valve. The pressure above the main valve disc generates a net downward force, hold the main valve closed.
When system pressure reaches the set pressure, the pilot spindle lifts and reseat piston closed simultaneously, venting the dome pressure through the pilot valve to atmosphere. Because of system pressure remains above reseat pressure, the reseat piston is hold  tightly closed, blocking flow to the pilot valve (the non-flowing pilot valve feature), at this time, the dome pressure of main valve is depressed quickly, allowing the main valve to open fully.
When the desired system pressure is achieved, the pilot spring force overcomes force on the reseat piston, the reseat piston snaps open, and the pilot spindle snaps closed simultaneously. Finally, system fluid reenter the dome and closes the main valve.
Pilot Operated Safety Valve Performance
1. The allowable tolerance of the set pressure: ≤3% of the set pressure
2. Overpressure: ≤10% of the set pressure
3. Blowdown: ≤10% of the set pressure
4. Sealing: Keep good sealing after valve discharge, according to API 527
Pilot Operated Safety Valve Features
1. The soft seat design makes sure the safey valve have good sealing performance before or after relief.
2. Allowing the working pressure nearer the set pressure without leakage.
3. When there is little overpressure, the safety valve can achieve in full open quickly.
4. The safety valve action performance and open do not be affected by back pressure.
5. Adjustable blowdown
6. Non-flowing pilot valve construction design reduces the harmful medium discharge and environmental pollution.
Pilot Operated Safety Valve Product Range
1. Safety valve pressure: 150LB - 2500LB
2. Safety valve size: 1" - 2"
3. Safety valve materials: WCB, CF8, CF8M, special steel
Pilot Operated Safety Valve Applicable Standards
Design: API RP520
Center to face dimension: API526
Flange standard: ANSI B16.5a
Inspection and test: API527