Pilot-operated safety valve

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I. Terminology: Pilot-operated safety valve: A type of safety valve that is driven or controlled by the medium discharged from a pilot valve; this pilot valve itself must be a directly-loaded safety valve that meets standard requirements. II. Working Principle: A pilot-operated safety valve consists of a main valve and a pilot valve; the pilot valve operates in response to changes in the pressure of the fluid in the system, while the main valve is actuated or controlled by the pilot valve. The main valve is a true safety valve, driven and controlled by the medium discharged from the pilot valve ； The pilot valve is used to sense the pressure in the equipment system, control the opening and closing of the main valve, and ensure the sealing performance as well as other performance parameters of the pilot-operated safety valve. The pilot valve is itself also a directly-loaded safety valve. When the medium pressure reaches the opening pressure of the pilot valve, it opens first, thereby sending the discharged medium to the main valve in order to drive and control the opening of the entire pilot-operated safety valve. Image: Principle of operation of a pilot-operated safety valve. When the system being protected is operating normally, the valve disc of the pilot valve remains closed. System pressure enters the chamber above the valve disc (piston) of the main valve through conduits and the pilot valve, from the inlet of the main valve. Since the area of the piston is larger than the area of the valve disc’s sealing surface, the system pressure exerts a downward force on the valve disc, keeping the main valve in a closed and sealed state. When the system pressure rises to the set pressure, the pilot valve opens, and at the same time the spool moves upward to block the air inlet passage of the pilot valve. The medium in the chamber above the main valve disc is discharged through the open pilot valve, reducing the pressure (chamber pressure) above the main valve disc; the main valve disc then opens under the influence of the inlet pressure, thereby allowing the system to release pressure. When the system pressure drops to a certain level, the pilot valve returns to its original position, causing the push rod to push the spool open. The system pressure then flows through the pilot valve into the chamber above the main valve’s disc, pushing the main valve disc to close. III. Applications: The main valve of a pilot-operated safety valve is typically loaded by the pressure of the medium, and the magnitude of this load is not limited; therefore, it is suitable for high-pressure and large-diameter applications ； Secondly, since its main valve is driven and controlled by the medium pressure, it can maintain a high closing pressure under normal operating conditions, that is, before the safety valve opens. As a result, the pilot-operated safety valve exhibits excellent sealing performance, even when the operating pressure is close to the set pressure ； Furthermore, the operation of the pilot-operated safety valve is less affected by changes in back pressure ； Finally, when it is necessary to confirm the setting pressure online, a pilot-operated safety valve can be selected.