By Shane Darville, P.E., CFEI

Pressure is a useful tool that accomplishes incredible tasks (like moving a train!), yet it can also become incredibly dangerous if it is not properly controlled. A buildup of pressure can lead to vessel failures, ruptures, or even explosions with catastrophic results.

Some of the most important pieces of equipment for controlling pressure are called Pressure Relief Valves. Relief valves are typically designed to vent and control a buildup of pressure before it reaches unsafe levels and causes catastrophic damage or injury. Pressure relief valves (sometimes called safety relief valves), should be sized and applied correctly to each individual situation. A relief valve for a one-inch line carrying liquid propane at 300 psi will usually be a small, hydrostatic relief valve because it typically will not have to vent much liquid propane to relieve pressure. A relief valve for an eight-inch pipeline carrying steam at 15 psi will typically be a much larger, pneumatic relief valve because it typically will have to vent a lot of steam to relieve pressure. There are even some vessels that are so large that they require a manifold of four, three-inch relief valves to vent fast enough to reduce the buildup of pressure.

Figure 1. 1/2-inch, 450 PSI, Hydrostatic Relief Valve.

Not only must pressure relief valves be sized and applied correctly, but they must also receive proper testing, maintenance, and service. Most applications and manufacturers require testing and maintenance on a regular schedule to determine if a relief valve is still fit for service. Testing is required because there are many things that can cause a relief valve to malfunction – e.g. corrosion, spring creep, and improper cleaning.

Figure 2. Manifolded Pressure Relief Valves for 50,000 Gallon Vessel.

The Engineers here at Bison Engineering have analyzed, tested, and testified about many different pressure relief valves that were used in a multitude of applications. We have developed a proprietary system that allows us to monitor and record a test on the relief valve and see the pressure at which the valve opens, the pressure at which the valve vents, and the pressure at which the valve reseats. This allows us to capture the testing data and create graphics that clearly and accurately show how the relief valve functioned.

Give us a call today to see how we can help you investigate and testify about a pressure relief valve that is involved in your case!