Safety valves must be adjusted to close after blowing down not more than which percentage?

Safety valves are critical components in any boiler system, designed to protect against overpressure by releasing pressure when it exceeds a predetermined limit. The adjustment of safety valves is governed by regulations to ensure reliability and effectiveness in protecting the system.

The requirement for safety valves to close after blowing down not more than 4% but not less than 2 lbs psi is established to ensure that the valve can maintain an adequate safety margin without allowing excessive pressure fluctuations. Having a blowdown set within these parameters ensures that the valve does not close too quickly, which could lead to the potential for pressure to rise beyond safe levels again. A blowdown limit of 4% allows the valve to operate efficiently without compromising safety.

This particular standard ensures that while the valve is performing its safety function, it also allows the boiler pressure to stabilize at a safe level upon closure. This is vital in maintaining operational integrity during high-demand situations or system fluctuations, making the correct adjustment essential for safe boiler operation.