American Society of Mechanical Engineers (ASME) Practice Exam 2025 - Free ASME Practice Questions and Study Guide

Safety valves are critical components of pressure vessels, such as boilers, designed to protect against overpressure by releasing excess steam or gas. Testing these valves by hand is essential to ensuring they function correctly in case of an emergency.

The correct condition for testing safety valves by hand is when the boiler steam pressure is not less than 75% of the set pressure. At this pressure level, the safety valve is sufficiently engaged to provide assurance that it will open under conditions approaching its designed pressure threshold. Testing at this level allows for the observation of how the valve functions under near-operational conditions, confirming it will release pressure effectively when required.

Testing safety valves at lower pressure levels, such as the water temperature being below 100°F or the boiler steam pressure being less than 50% of the set pressure, would not provide a reliable indication of valve performance. Furthermore, testing at full load does not necessarily correlate with the position of the safety valve and its proper function. Thus, the 75% threshold strikes a balance between safety and functional testing.