Is it standard practice to use a pressure relief valve as a pressure regulator?

Question

I'm attempting to understand the difference between a pressure relief valve and a pressure regulating valve. From my research far, I've come to the following conclusion:

• Pressure relief valves are primarily used for limiting pressure build ups and are often safety related. Pressure relief valves vent the fluid when the pressure exceed some setpoint.

• Pressure regulator valves on the other hand are used to regulate a pressure via step-down. These regulator are typically non-venting.

So I'm somewhat confused as to whether or not I should be using a pressure relief valve or pressure regulator in my application. It seems like a pressure relief valve would do the same exact thing as a regulator except it would vent the gas. Do pressure regulator offer better regulation than a relief valve?

Answer 1

Sort of.

Certainly things like pressure cookers and turbochargers use blow off vales as a routine way to regulate pressure.

Generally this is to make sure that internal pressure doesn't exceed some design maximum rather than for fine control and it is a bit contextual as it tends to imply that whatever working fluid you are dealing with goes to 'waste'. Obviously in both of the above examples this doesn't really matter much.

In the case of a turbo charger both the fluid and the energy to compresses it are more or less 'free' once you have the physical plant in place so a blow off valve is a simple and reliable way to regulate pressure.

In contrast if you have something like industrial argon as a welding shielding gas you don't want to vent that to atmosphere if you don't need to so you would use a more sophisticated regulator to control the flow-rate indeed y ou mmight even use two, one for course pressure regulation and one for fine volume flow-rate control.

Equally in a more general case if you are using bottled gas the unregulated pressure is directly related to the mass of gas in the cylinder so are often forced to use a regulator unless you can accept a drop-off in available pressure with usage.

As an aside several Robot Wars Robots have used direct bottle pressure (CO2) ie just a solenoid valve and no regulator to fire weapons, flippers etc. This tends to give fairly fierce performance while the bottle is full and is simple to implement, especially by remote control but every time you use it the available pressure drops and so can be a bit inefficient.

Answer 2

Id say a regulator is more optimised for attaining a given setpoint with precision and lack of chatter, whereas a relief valve is more concerned with reliability and less with finesse. But you are correct on an abstract level they are both flow control feedback mechanisms of a very similar kind; though in practice you are unlikely to confuse the two application wise. Without regretting it that is.