Why Do I Need a Pressure Relief Valve?

In a high-pressure gas system, a regulator is used to control the flow of gases at a set pressure rating. Regulators often have a built-in pressure relief valve (PRV), but this may be factory set at a pressure above the rated pressure of CRS purifiers, especially with plastic-bodied or glass purifiers. The regulator's PRV may also fail.

What is a high-pressure gas source? A common example is any of the compressed gas cylinders that supply GC carrier gas or fuel lines (FID). Helium, air, or hydrogen cylinders, when full may have pressures approaching 3000 psi / 200 bar, well above the allowed pressure of most point-of-use gas purifiers. If any pressure-regulating device downstream of the cylinder and upstream of the gas filter should fail, dangerous overpressure can occur at the instrument or in the line. Like any device, gas regulators age with use, and they can fail. Regular inspection and testing of the equipment can reduce risk tremendously, but it needs to be recognized that overpressure can cause damage to property, and harm or serious injury to personnel.

Each organization's safety management will have its own take on this issue, but at CNM, we consider it best practice to install a dedicated pressure relief valve (PRV) downstream of every regulator, set for the lowest maximum pressure rating of the gas purifiers or instruments downstream of the purifier. In case of regulator failure, we expect protection from this secondary relief valve. In the case of toxic or flammable gases, or if we identify an asphyxiation hazard, we connect the vent port of this valve to a vent line routed to the outside of the building.

When we set up the pressure relief valve, we examine the piping, the low-pressure side of the regulator, and all downstream equipment for maximum pressure ratings. We set the PRV to the lowest maximum pressure rating of the system components. This is the MAXIMUM ALLOWABLE PRESSURE for the entire system.

At CNM, we use several types of PRVs that have various functions in our operations. For questions about this blog post or more information on how to use PRVs with CRS products, please contact us.