What is a back pressure regulator?

In the past, we have fielded questions about back pressure regulators (Type-700BP) and have discovered some confusion on how it should be used. We should start off by saying the 700 back pressure regulator does not function like a normal air regulator.  Some of the confusion may be due to the name, which includes the term “regulator” and the fact that it looks exactly like our Type-700 regulator. For the sake of this discussion, it would be better to call the 700 BP a “precision relief valve“. Many times we see this being used downstream from another regulator and is being used to dump pressure to atmosphere or some other capture device.

Then why would we not just use a normal regulator and rely on the “built-in” relief valve? Using a back-pressure regulator, like the 700BP, will allow a much larger exhaust capacity than trying to use the internal relief valve of a regulator. Some may use a 700BP with a normal relieving regulator to build in another level of safety, just to be sure the downstream pressure does not build due to a failing regulator or unexpected increase in flow due to a large exhaust requirement. If a standard regulator and relief valve are used together, it would be wise to set the relief valve 5 to10 psi above the regulator set pressure to avoid feedback and chatter issues between the two valves.