The 106-PR-R and 206-PR-R pressure reducing and pressure sustaining valves are based on the 106-PG or 206-PG main valve with the addition of the sustaining pilot 81-RP and pressure reducing pilot PR-160.
Provided the upstream pressure setting is satisfied, the 81-RP pilot is kept open, permitting the valve to be controlled by the 160 pilot. The 160 pilot senses downstream pressure and under flowing conditions, it reacts to small changes in pressure to control the valve position by modulating the pressure above the diaphragm.
Should high demand cause the inlet pressure to fall to the 81-RP pilot setting, the upstream pressure has priority and the valve will modulate to prevent the upstream pressures from dropping below the set-point.
When the valve is modulating to sustain upstream pressure above the minimum 81-RP pilot set-point, the downstream 160 pilot may try to open the valve to maintain its set-point, but upstream has priority and downstream pressures will fall below expectations.
In typical applications, the reduced port model 206-PR-R is often the best selection.
For more information on the 106 / 206-PR-R pressure reducing valve: