Safety valve for hydrogen service

Hydrocracking units are equipped with pilot-operated safety valves in both the cold high-pressure section tops and the main seal gas tanks of the recycle hydrogen compressor. A pilot-operated safety valve is a type of safety valve that consists of a main valve and a pilot valve; the pilot valve acts on its own in response to the pressure of the system fluid, thereby controlling the opening and closing of the main valve. Pilot-operated safety valves are particularly suitable for applications with high back pressure, large flow rates, high pressures, and in locations where space is limited. 1. Working principle: When the system is operating normally and the pilot valve is in the closed position, the system pressure is transmitted through the inlet pressure pipe, the pilot valve, and the air chamber pressure pipe to the dome-shaped air chamber at the top of the main valve’s disc. This creates a downward net force on the main valve disc, keeping it in the closed position. When the system pressure reaches the set pressure, the pilot valve opens and the shuttle blocks the air inlet channel of the pilot valve; the pressure in the main valve’s air chamber is then released through the pilot valve. Since the system pressure is higher than the returning pressure, the shuttle closes the air inlet channel, thereby preventing fluid flow within the pilot valve. At this point, the pressure in the main valve’s air chamber drops sharply, the valve disc of the main valve opens completely, and the fluid is discharged through the main valve to reduce the pressure. When the system pressure drops to a certain level, the spring force of the pilot valve overcomes the force exerted on the shuttle by the pressure at the valve inlet; the pilot valve returns to its original position, the push rod pushes the shuttle aside, and this allows the fluid to flow back into the dome chamber of the main valve, thereby closing it. 2. Features: (1) The soft-seal valve seat ensures good sealing performance before and after the safety valve operates. (2) Allow the operating pressure to be close to the set pressure of the safety valve. (3) A relatively small overpressure is sufficient to cause the main valve of the safety valve to reach its fully open state quickly. (4) The operating performance and opening height of the safety valve are not affected by back pressure. (5) The opening and closing pressure difference is adjustable. (6) The non-flowing structure design of the pilot valve reduces the emission of harmful substances and environmental pollution. (7) The set pressure of the safety valve can be detected online. 3. Operating procedures: (1) To activate the safety valve, activate the secondary valve first and then the main valve. (2) To deactivate the safety valve, deactivate the main valve first and then the secondary valve