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 160 PR.
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.