What percentage of pressure will cause a safety valve to lift completely?

The correct answer indicates that a safety valve will typically lift completely when the pressure reaches 3% above the set pressure. Safety valves are designed to relieve excess pressure in a system to prevent dangerous situations such as explosions or system failures.

When the pressure exceeds the set limit, the valve starts to lift off its seat. The standard operation for many safety valves is to begin lifting at a specific percentage above the set point, with the valve fully lifting at 3% overpressure. This is crucial in maintaining safety within the system, as it allows for controlled venting of steam or gas, thus preventing potential hazards.

Understanding the function and operation of safety valves, including the specific percentage at which they lift, is vital for anyone working with low-pressure boilers and their safety systems.