Pneumatic pressure regulators are common and very important in web-handling lines. They are used in several parts of the drive system. In particular, I am thinking of dancers and accumulators. Dancers and accumulators set web tension with air pressure in pneumatic cylinders. The performance of the pneumatic-pressure regulator directly affects tension performance.
An article in the October 2012 issue of Industrial Process Products & Technology titled "How to Read a Regulator Flow Curve Part 1: The Basics" by Bill Menz with Swageloc discusses an important issue in selecting the correct regulator.
The regulator should be selected to hold pressure for the expected air flow for the application. Regulator vendors provide a flow curve or family of curves showing Outlets Pressure (psig) vs. Flow (ft^3/min) for various pressure setpoint. The curves are not flat and pressure may drop by 45% as flow increases.
Let's consider a dancer with two cylinders with 2 in^2 area each. With out of round unwind rolls, we can expect the cylinders on the dancer to move 6 in. with every revolution of the unwind roll (about every second). The volume change in the two cylinders would then be 2*2*6*60=1440in^3/min=0.83ft^3/min. This is a low flow. The selected regulator and associated tubing must be capable of holding pressure when the flow changes.
Note that for half the cycle the regulator is passing air and the other half cycle it is bleeding air to atmosphere. The regulatory should be capable of holding pressure with flow in either direction.