Properly Select Pressure Relief Valves
Jane Alexander | May 14, 2018
Pressure-relief valves protect vessel-piping systems and other plant equipment from dangerous situations. But they’re not a one-size-fits-all solution.
Selecting the wrong type for an application can lead to problems. Selecting the right type can help ensure smooth plant operations and minimize safety risks. CPV Manufacturing, Kennett Square, PA (cpvmfg.com), points to several important design-related considerations when choosing pressure-relief valves for specific applications.
Pressure-relief valves are available in different metals, each of which is meant to cater to specific applications. Depending on the system, a valve made with a certain material may be needed to ensure safety and proper operation. For example, stainless-steel designs have properties that allow them to work best in plants with corrosive materials.
CONNECTION SIZE AND TYPE
Just as pressure-relief valves come in a variety of metals, they also come with different sizes and types of connections. According to the National Board of Boiler and Pressure Vessel Inspectors, Columbus, OH (nationalboard.org), a correctly sized valve must be at least as big as the inlet and discharge piping. It’s also important to note that certain valves are designed for specific connector types.
Pressure-relief valves are, by their very nature, designed to withstand great amounts of pressure and high temperatures. Still, each device has its own specific limits. The set pressure is the pressure that causes the valve to open, and it’s measured in pounds per square inch (PSIG). Again, according to the National Board of Boiler and Pressure Vessel Inspectors, the set pressure of the valve cannot exceed the maximum allowable working pressure. A valve with a set pressure less than the maximum allowable working pressure, however, is acceptable.
Back pressure (the pressure on the outlet side of the valve from the discharge system) will also contribute to the maximum allowable working pressure of a valve. This factor can be constant or variable, according to the plant’s operation. Constant back pressure will require a pilot-operated valve. Variable valve pressure cannot exceed 10% of the valve set pressure.
Pressure-relief valves can also withstand high temperatures. Specific metals, though, can only handle certain temperatures. Thus, to ensure proper valve selection, the system temperature must be taken into account.
While pressure-relief valves can alleviate a great amount of pressure, they do have their limits. The maximum capacity of pressure they can relieve depends on multiple aspects, including the valve design and the temperature of the liquid or gas flowing through it. EP
For more information on a wide range of fluid-control topics, including choosing valves, fittings, and other products, visit cpvmfg.com.