What percentage of operating pressure is required to lift safety valves by hand?

The correct answer is that 75% of the operating pressure is required to lift safety valves by hand. Safety valves are crucial components in pressure systems, designed to prevent pressure from exceeding safe limits. The specific requirement of 75% ensures that the valves can be tested effectively while remaining within a safe operational margin. By applying this pressure, the technician can confirm that the valve will open under actual operating conditions, validating its functionality and readiness to relieve excess pressure when needed. This percentage helps in ensuring operational safety, as it is high enough to demonstrate that the valve will operate properly without risking premature activation during normal operations. This provides confidence that the safety system will function correctly under high-pressure situations.