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What is a relief valve?

ressure relief valve, also known as safety valve, is a crucial safety protection device. The main function is to automatically open and release excess pressure when the pressure inside the system exceeds the predetermined safety value, in order to prevent equipment or pipelines from being damaged due to overpressure and ensure the safe and stable operation of the system.

I. Working principle

The operation of the pressure relief valve is based on the principle of pressure balance. Taking the common spring type pressure relief valve as an example, under normal pressure conditions, the valve disc is tightly adhered to the valve seat by the elastic force of the spring, preventing the medium from flowing. Once the system pressure rises above the opening pressure set by the spring, the force of the medium on the valve disc overcomes the spring force, the valve disc is lifted, the valve opens, the medium is discharged, and the system pressure decreases accordingly. When the pressure drops to the appropriate range, the spring force causes the valve disc to reset, closing the valve and stopping pressure relief.

II. Structural composition

Valve seat: Provides support for the entire valve and is also the channel interface for the medium to flow in and out. It is connected to the pipeline or equipment to ensure the normal flow of the medium.

Valve disc: As the core component that controls the opening and closing of valves, it switches between open and closed states according to changes in system pressure, determining whether the medium is discharged.

Spring: A key component that determines the opening pressure of a valve. By adjusting the preload of the spring to set the opening pressure, its elastic performance directly affects the accuracy and sensitivity of the valve’s operation.

Adjustment mechanism: Used to accurately adjust the opening and closing pressure of valves, generally composed of adjusting nuts, screws, etc. By rotating the adjusting nut to change the degree of spring preload, the pressure setting can be adjusted.

Sealing components: Such as gaskets between the valve disc and seat, and sealing rings between the valve stem and cover, ensure the sealing performance of the valve when closed and prevent medium leakage.

III. Structure type

• Spring type relief valve: Relying on the elastic force of the spring to control the valve action, the structure is simple and compact, easy to install, and widely used in systems with various pressure and temperature conditions. However, springs are prone to fatigue during long-term use and require regular inspection and maintenance.

• Heavy hammer relief valve: It uses the gravity of the heavy hammer to counteract the pressure of the medium. When the pressure of the medium exceeds the set pressure of the heavy hammer, the valve disc opens. This type has a simple structure, high reliability, and is not affected by temperature, but it has a large volume and poor sensitivity, and is commonly used in large equipment or high-temperature environmental systems.

• Pilot operated relief valve: It works in conjunction with the main valve and pilot valve. The pilot valve monitors the pressure of the system. When the pressure exceeds the standard, the pilot valve opens to guide the medium into the main valve control room, change the pressure difference on both sides of the main valve disc, and open the main valve to release pressure. Its advantages are large displacement, high sensitivity and accuracy, suitable for high-pressure and high flow systems, but its disadvantages are complex structure, high cost and maintenance difficulty.

• Pulse type pressure relief valve: Using pulse signals to control the opening and closing of the main valve, commonly used in special systems that require extremely high pressure control accuracy, such as certain key pressure protection links in nuclear power plants.

IV. Main function

• Safety protection: Prevent serious accidents such as equipment rupture and explosion due to overpressure, and ensure the safety of equipment and personnel life and property. 

Pressure regulation: When the system pressure fluctuates, it should be opened and closed in a timely manner to maintain the system pressure within a safe and stable range, ensuring reliable operation of the system.

• Leakage prevention: Keep it closed during normal operation to effectively prevent medium leakage, reduce energy loss and environmental pollution.

V. Application Fields

• Petrochemical industry: In petroleum refining and chemical production, a large number of high-pressure, flammable and explosive media processing equipment, such as reaction vessels, storage tanks, pipelines, etc., cannot do without the safety protection of pressure relief valves.

• The power industry: Whether it is boilers, steam turbines for thermal power generation, or related equipment for hydroelectric power generation, pressure relief valves play a critical protective role to prevent equipment damage due to abnormal pressure.

• Pharmaceutical industry: Drug production has strict requirements for environmental and equipment safety, and pressure relief valves are used in reaction vessels, sterilization equipment, etc. to ensure the quality and safety of drug production.

• Food and beverage: In pressure vessels and piping systems used in food and beverage production, pressure relief valves ensure safety and hygiene during the production process, preventing pressure issues from affecting product quality.

• Water treatment: Used to regulate and protect equipment such as water pumps and pipelines, avoiding equipment damage caused by high pressure and ensuring the normal operation of the water treatment system.

• Aerospace: In critical areas such as hydraulic and fuel systems of aircraft, pressure relief valves ensure the safe operation of the system under extreme working conditions, ensuring flight safety.

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