Your pressure relief valves (PRVs) are your most important line of defense against equipment damage, not to mention harm to your personnel, your plant, and the environment. Because of this, it’s important that you install and operate them correctly.
We get a lot of questions about the correct procedures for installing and operating PRVs. The guidelines below provide answers to the most common questions and solutions to the most common problems our customers have.
Pressure relief valve installation
- Mount PRVs in a vertical position, which means upright and with the spindle vertical. A valve installed in any position other than vertical might not perform correctly.
- For flanged valves, be sure to draw the bolts down evenly. This is especially crucial for cast iron valves. If you tighten one side all of the way and then the other, not only will you not be able to tighten it completely, but you could crack the valve.
- Avoid overtightening the valve. This can damage both the inlet and the outlet threads and cause leakage.
- Apply pipe dope to the male threads only. Pipe dope is a compound that prevents valves from leaking, but if you apply it to the female threads, it could contaminate your system.
- The inlet piping should be short and direct. The inlet should never have a smaller diameter than the valve itself. This will constrict the flow of steam, air, or other media.
- The inlet should never be located near excessive turbulence on the vessel.
- The outlet piping should always be supported. If it isn’t, it can weigh down and warp the valve, which will cause the valve not to seat properly. This can lead to excessive leakage.
- The nominal size of the outlet piping should be as large or larger than the valve outlet size. If it isn’t, the flow will be restricted and the valve won’t relieve as much capacity as it’s supposed to.
- The outlet piping should not produce any strain due to thermal expansion. As the medium expands, if the piping doesn’t have any give, the valve can warp and leak.
Pressure relief valve operation
- Avoid operating the valve too close to the set point. Doing this can cause simmer and leakage. Once this starts, it will only get worse.
- Avoid testing your valve too often. Lifting the test lever too often can allow dirt or other foreign matter to get into the seat, which can cause the valve to leak. While regular testing is a recommended part of a preventative maintenance program, this should only be done about once a year, not once a month.
If you have any questions about your PRVs or need additional advice about installation or operation, give us a call. At the end of the day, a PRV is a safety device, so it’s imperative you get it right.