What is relief capacity and why should you care?

General-purpose regulators have a relatively low relief flow capacity when compared to their forward flow abilities.  In most applications, this is not a problem.  Generally, there is very little build-up in downstream pressure in steady flow applications.  For instance, in normal valve actuator applications, the filter regulator is there to simply supply a valve positioner/actuator with a steady supply of regulated air.

But what happens if you need to bleed off air quickly when downstream pressure builds past a set point?  This can happen when you are commissioning valve actuators and trying to set stroke and other set points.  Standard regulators have very minimal relief capacity compared to forward flow capabilities.  This can be an issue when trying to bleed off air while testing actuators…especially large volume actuators that take long periods of time to bleed down.  See the video below to compare a standard regulator (Type 300) with our Type 100 precision regulator while working a valve actuator.  In addition,  when setting a volume of air to a specific pressure, it can be difficult to find the exact set point with regulators that have a low relief capacity.  The exhaust rate is dependent on the size of the relief valve located in the diaphragm assembly.

Another application where downstream pressure builds quickly is a pneumatic counter-balance cylinder.  These cylinders are sometimes used in assembly lines to “zero out gravity” and augment the lifting capabilities of individuals.  Because the movements can happen at a high velocity, standard regulators do not have the relief capacity to deal with these high volumes of back pressure created by the cylinder.  This is where our high relief and extra high relief capacity Type 100 regulators work extremely well.

See the chart below for relief capacity specifications to better understand the difference.