What is the maximum allowable safety valve blowdown percentage of the set pressure?

The maximum allowable safety valve blowdown percentage of the set pressure is 3%. This value is significant because it ensures that safety valves provide an effective and reliable means of pressure relief. Blowdown refers to the difference between the lift (or opening) pressure of the safety valve and the reseat pressure once the valve closes.

By limiting the blowdown to 3%, it minimizes the risk of the boiler operating excessively near its maximum allowable working pressure, which could lead to potential safety hazards or system failures. Maintaining a blowdown of this percentage allows for the valve to react promptly to pressure changes while ensuring that it reseats quickly once the pressure returns to a safe range.

Understanding this percentage is crucial for the safe operation of high-pressure boilers, as it helps in correctly sizing and selecting safety valves for specific applications based on the required standards and regulations.