The 106-PR-C and 206-PR-C pressure reducing and check valves are based on the 106-PG or 206-PG main control valve.
The pilot valve senses the downstream pressure through a connection at the valve outlet. Under flowing conditions, the pilot reacts to small changes in pressure to control the valve position by modulating the pressure above the diaphragm. The downstream pressure is maintained relatively steady at the pilot set-point.
The pilot check valves direct downstream pressure above the diaphragm to close the valve when the system pressures reverse (when the downstream pressure is higher than the upstream).
In typical pressure reducing applications, the reduced port model 206-PR-C is often the best selection.
For more information on the 106 / 206-PR-C pressure reducing valve: