How Does a Lever Safety Valve (Weight-Loaded Safety Valve) Work?
A lever safety valve, also commonly known as a weight-loaded safety valve, is a fundamental type of pressure relief device. Understanding its working principle is key for applications in low to medium-pressure systems like boilers.The main safety valve product names of China Safety Valve Network include:Impulse Safety Valve,Impulse Spring Safety Valve,JIS Safety Valve,Main Safety Valve,Overflow ValveOil Refining Specific Safety Valve,Pulse Safety Valve,Pilot Safety Valve,Pressure Safety Valve,Quick Switching Safety Valve,Spring Low Lift Safety Valve,Spring Low Lift High Pressure Safety Valve
Components and Working Principle
The valve consists of a valve body, seat, disc (or valve plug), lever, and a counterweight (or weight).
The operation of a weight-loaded safety valve is based on the balance of moments (torque) around a fulcrum:
Closed Position: The force of the counterweight is transmitted through the lever and onto the valve stem. This force presses the disc tightly against the seat, keeping the valve closed and preventing fluid (e.g., steam) from escaping.
Opening (Relief) Process: The system pressure acts upward on the bottom area of the disc. When the system pressure rises to the set point, the upward force created by this pressure generates a moment around the fulcrum that exceeds the moment created by the counterweight.
Pressure Relief: This imbalance causes the lever to pivot, lifting the disc off its seat. The pressurized fluid (steam) is then discharged to a safe outlet, reducing the system pressure.
Resealing: Once the system pressure drops below the reseat pressure (slightly below the set pressure), the moment from the counterweight again exceeds the fluid force moment, forcing the disc back onto the seat and closing the valve.
Pressure Adjustment: The set pressure of the safety valve is easily calibrated by adjusting the position of the counterweight along the lever. Moving the weight farther from the fulcrum increases the set pressure, while moving it closer reduces it.
Advantages, Disadvantages, and Applications
Advantages:
Simple and robust construction
Easy to adjust and maintain
Offers reliable performance without requiring an external power source
Disadvantages:
Large size and heavy weight compared to spring-loaded valves
Limited suitability for high-pressure or high-capacity systems due to the massive weights required.
Typical Applications:
Lever safety valves are well-suited for small to medium-sized, low-pressure boilers. In high-pressure, large-capacity utility boilers, they are often used as the pilot valve (or pulse valve) in a more complex pilot-operated safety valve system.

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