Tips for Selecting and Operating Pressure Relief Valves

Pressure relief valves are the best insurance you have against safety incidents in plants and along pipelines. We get a lot of questions from customers about how to select and operate pressure relief valves. Here are answers to three of the most common questions we hear.

Can I reset the pressure on a pressure relief valve?

Yes, pressure relief valves can be reset under the VR or T/O stamp program with inspection by an authorized valve repair company. Some repairs may be necessary before the valve can be reset. For example, the valve may need a spring change.

Warning: PRVs should NOT be reset above the maximum allowable working pressure (MAWP) of the vessel or equipment being protected. We’ve seen this happen, and it presents a major safety risk. Before resetting the pressure on a valve, make sure that the pressure you want is within the MAWP and allowable set pressure range for the manufacturer’s valve series.

I’m operating close to the set point on my valve. How can I keep it from simmering or lifting?

In general, the operating gap will vary depending on the system and valve type. Most pressure relief valves can be operated at up to 90% of the set point. Some metal-seated valves may get up to 94%, and some soft-seated valves over 101 psi can handle operating pressures up to 95% (for example, the Consolidated 1900 series with a soft seat can handle this higher pressure). If you exceed those thresholds, the valve will simmer. This can damage the valve and will more than likely lead to leakage and system downtime. Here are three things you can do to reduce simmer on your valves.

1. Lower Your Operating Pressure

Many companies operate valves at higher pressures because they want to increase production. However, this often leads to the exact opposite result.

Here’s an example. Imagine a valve that opens at the tag pressure and has a 7% to 10% blowdown. That means the valve would blowdown to 90% of nameplate set pressure. In other words, it would hold tight to 90%. If you were to operate that valve at 91% or 92%, you would risk pushing the valve into simmer and possibly actuate the valve with very little system fluctuation. This would more than likely cause valve leakage and damage and increase your downtime.

Alternatively, if you were to operate the valve at 90%, rather than 91% or 92%, you would reduce the likelihood of pushing the valve into simmer or actuating the valve. This would, in turn, reduce the chances of valve leakage and damage, and decrease your downtime.

In other words, reducing your operating pressure can actually increase production, not reduce it.

1. Use a Pilot-Operated Relief Valve

In some situations, switching to a pilot-operated relief valve can allow you to operate at 95% to 98% of the set point.

1. Switch to a Soft-Seated Valve

Particularly in areas with high vibration, a soft-seated valve will allow you to operate the valve at a higher pressure.

I need a new pressure relief valve. What information do I need to provide?

When replacing a pressure relief valve, it’s common for companies to just replace it with a valve with the same nameplate information. This may be fine if the valve was not causing a problem, but if the valve is a bad actor, it’s possible that it wasn’t the right valve for the application in the first place.

We recommend always verifying the sizing and selection of a replacement valve. Download a sizing sheet for steam, air, and liquid pressure relief valves.

You may even need to consider a different type of device than currently installed.

Have a question about your pressure relief valves? Ask us!