Efficient Plant May 2018 - 33

fluid control

Properly Select
Pressure
Relief Valves

VALVE MATERIALS

CONNECTION SIZE AND TYPE

Installing the right valve for an application can help ensure smooth
operations and provide crucial protection and safety.

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.
- Jane Alexander, Managing Editor

For more information on a wide range of fluid-control topics, including
choosing valves, fittings, and other products, visit cpvmfg.com.

MAY 2018

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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.

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.

SET PRESSURE
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
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 pilotoperated valve. Variable valve pressure cannot exceed 10% of the valve
set pressure.

TEMPERATURE
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.

REQUIRED CAPACITY
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
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Table of Contents for the Digital Edition of Efficient Plant May 2018