Definition and function
A relief valve is an automatic valve that uses the force of the medium itself to discharge a certain amount of fluid without the aid of an external force to prevent the pressure in the system from exceeding a predetermined safety value. When the pressure returns to normal, the valve will close itself and prevent the medium from continuing to flow.
Structure and Composition
Relief valve is usually composed of valve seat, valve flap, spring and other components. The valve seat is the contact surface of the valve flap when it closes to ensure the sealing; the valve flap is the key component, when the system pressure exceeds the set value, the valve flap will be pushed away from the seat to release the pressure; the spring provides the closing force, when the system pressure is lower than the set value, the spring will press the valve flap back to the seat to restore the sealing.
Classification
Spring-loaded relief valves: the opening pressure of the valve is adjusted by the force of the spring, which is the most common type of relief valve, widely used in small and medium-sized pressure vessels and piping systems in petroleum, chemical, and electric power industries.
Weighted hammer relief valve: using the gravity of the hammer to balance the medium pressure, mostly used in large boilers.
Pilot operated relief valve: It has two parts: main valve and pilot valve, and the pilot valve controls the opening and closing of the main valve, which is suitable for high pressure and high flow rate occasions.
Rupture Disc Relief Valve: When the pressure reaches the set value, the rupture disc ruptures and releases the pressure. Commonly used in applications where leakage is not allowed, such as compressed air storage tanks.
Installation and Use
The relief valve should be installed vertically in the gas phase space of the equipment or pipeline, and the outlet should be facing the safe direction. During installation, attention should be paid to keep the relief valve clean to prevent impurities from entering the valve and affecting its normal operation. The installation location should be convenient for inspection and maintenance, while avoiding the influence of high temperature or corrosive medium.
Maintenance and Inspection
The relief valve should be inspected at least once a year, including dynamic inspection and disassembly inspection. The steps of dynamic inspection include assembly, pressurization, pressure holding, pressurization action, depressurization back to seat, and pressure holding again.