Set and Reset Pressure setting in boiler steam safety valve

Set and Reset Pressure Settings in Boiler Steam Safety Valves

Safety valves are critical components in steam boilers. They protect the system from overpressure conditions by automatically releasing steam when the pressure exceeds safe limits. Understanding the set pressure, reset pressure, and overpressure is essential for safe operation, efficiency, and compliance with boiler standards.  

🔍 Components Linked with Safety Valves

Two key parameters define the operation of a safety valve:  

1. Tonnage (Capacity) – The amount of steam the valve can discharge safely.  

2. Pressure – The set and reset pressure levels at which the valve operates.  

⚙️ Set Pressure

- Definition: The set pressure is the inlet static pressure at which the safety valve disc begins to lift off its seat.  

- When the boiler pressure rises above this value, the valve starts to open.  

- The spring inside the valve resists the lift; as the spring compresses, additional pressure is required for the valve to open further and allow significant steam flow.  

🌍 Overpressure

- Definition: The additional pressure rise required before the safety valve discharges at its rated capacity.  

- Typical Values:  

  - Steam boilers: 3% to 5% overpressure.  

  - Other applications: 10% overpressure.  

  - Compressible fluids: 3% to 10%.  

  - Liquids: 10% to 20%.  

- The allowable overpressure depends on industry standards and the specific application.  

🔄 Reset Pressure

- Definition: The pressure at which the safety valve closes again after discharging steam.  

- The difference between the set pressure and reset pressure is known as blowdown.  

- Blowdown ensures the valve does not chatter (rapidly open and close), which could damage the valve and reduce safety.  

📊 Practical Guidelines for Boilers

- For boilers up to 5 TPH (tons per hour):  

  - Set and reset pressure difference should be below 5%.  

- For boilers over 5 TPH:  

  - Set and reset pressure difference should be between 5% to 10%.  

These values ensure safe operation while minimizing unnecessary steam loss.  

✅ Importance of Correct Settings

1. Safety – Prevents dangerous overpressure conditions.  

2. Efficiency – Minimizes steam wastage and fuel consumption.  

3. Equipment Protection – Avoids damage to boiler tubes, drums, and piping.  

4. Compliance – Meets statutory requirements and industry standards.  

📌 Conclusion

The correct set and reset pressure settings in boiler steam safety valves are vital for safe and efficient operation.  

- Set pressure determines when the valve opens.  

- Overpressure ensures full discharge capacity.  

- Reset pressure ensures stable closure without valve chatter.  

By following recommended guidelines (3–5% overpressure for steam boilers and appropriate blowdown percentages based on boiler capacity), industries can achieve safe operation, reduced fuel costs, and longer equipment life.