Rotary Pump - Pressure Adjustment

How to adjust the pressure of your rotary pump.

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I wrote this article as a result of a forum post

"I was told never but never to adjust a rotary pump. Instead the OPV should be adjusted"

I am fairly sure the poster misunderstood the instructions they were given, so I thought this short article would help clarify things.

With a Rotary pump you NEVER adjust the OPV, you always make the pressure adjustment on the pump itself. There is a small screw on the side of the pump for this purpose and usually an outer locking screw that has to be loosened first as shown in the photo below (click to enlarge). The adjustment mechanism may look slightly different on different pumps, but the principle and method of adjustment is the same (some may not have a lock-nut). In all cases the centre screw is turned clockwise or anti clockwise to increase/decrease the pumps output pressure. usually the pumps have an internal "balanced bypass", so that under a defined range of input pressures pump output pressure will remain constant (outside this range the "balanced bypass" is ineffective). Some machines have pumps without an internal "balanced bypass", so you may have to adjust the pressure on installation, in line with your mains water supply inlet pressure.


On a rotary pumped machine, the OPV is there for 2 reasons and should be set (at the factory) to release pressure at 12 bar. If you ever wanted to check this you would have to set your pump temporarily to output 12 bar against a blind filter and then check the OPV just lets by. If it doesn't adjust it until it does….then reset the pump to 9 bar again.

  • As a safety device to vent should the balanced bypass pressure regulation on the Rotoflow rotary pump fail and the pumps output pressure climbs too high
  • To allow the brew boiler water (or Heat Exchanger water) to expand out of the OPV as it heats up to operating temperature (water expands about 4% when heated from room temp to 105C)….without the OPV, then the boiler/pipes could rupture.

The photo below shows a typical twin boiler rotary pumped machine with the OPV for safety and expansion purposes (possibly why it's also known as an "expansion valve")


With a Vibration pump machine the situation is completely different and the OPV is used to take the unregulated 15-18 bar output of a vibration pump and allow it to be regulated down to nearer 9-10 bar, by virtue of an adjustable (usually) spring and valve that lets by at these lower pressures. See opv-over-pressure-valve