Working principle and characteristics of pilot operated safety valve

Pilot operated safety valve is a type of safety valve composed of a main valve and a pilot valve. The pilot valve responds to the pressure of the system medium and acts on itself to control the opening and closing action of the main valve. Pilot operated safety valves are particularly suitable for applications in high back pressure, high flow, high pressure, and compact installation locations.

The main working principle of a pilot operated safety valve is that when the system is working normally and the pilot operated safety valve is in the closed state, the system pressure is transmitted to the dome chamber at the top of the main valve disc through the inlet pressure pipe, pilot valve, and chamber pressure pipe, thereby generating a downward net force on the main valve disc, causing the main valve to be in the closed state. When the system pressure reaches the set pressure, the pilot valve opens and the shuttle closes the intake passage of the pilot valve. The pressure in the main valve chamber is discharged and relieved through the pilot valve. Due to the system pressure being higher than the reseating pressure, the shuttle closes the intake passage, thereby blocking the flow of fluid in the pilot valve. At this time, the pressure in the main valve chamber drops sharply, and the main valve disc is fully opened, allowing the fluid to be released and depressurized through the main valve. When the system pressure drops to a certain value, the spring force of the pilot valve overcomes the force of the valve inlet pressure acting on the shuttle, the pilot valve returns to its seat, the top rod opens the shuttle, and finally allows the fluid to re-enter the dome chamber of the main valve, closing the main valve.

The main characteristics of a pilot operated safety valve are: 1. Soft sealing of the valve seat ensures good sealing before and after the safety valve trips; 2. Allow the working pressure to approach the set pressure of the safety valve; 3. A small overpressure can quickly make the main valve of the safety valve reach the fully open state; 4. The performance and opening height of the safety valve are not affected by back pressure; 5. Adjustable opening and closing pressure difference; 6. The non flowing structure design of the pilot valve reduces the discharge of harmful media and environmental pollution; 7. Can detect the set pressure of the safety valve online.

The operation steps of a pilot operated safety valve are as follows: 1. Activate the safety valve: first activate the sub valve, then activate the main valve; 2. Cut off the safety valve: first cut off the main valve, then cut off the sub valve