What is a pressure relief valve designed to do?

A pressure relief valve serves a critical safety function in various systems, particularly in pressure vessels and piping systems. Its primary purpose is to prevent excessive pressure buildup, which can lead to dangerous situations, including explosions or ruptures.

The valve is designed to open at a designated pressure, effectively providing a controlled outlet for excess vapor or gas when the internal pressure exceeds a certain threshold, usually around 250 psi in many industrial applications. By doing so, the valve releases vapor, thereby reducing the pressure within the container or system to a safer level.

Selection of both functions—opening at a specific pressure and releasing vapor—makes option C the comprehensive answer as it encapsulates the dual role of the pressure relief valve in maintaining safety and preventing overpressure conditions. Maintaining constant pressure, which is suggested in another choice, is not a function of a pressure relief valve; instead, that would be more aligned with the operation of a pressure control valve.