The 106-HC and 206-HC hydraulic check valves are based on the 106-PG or 206-PG main valve.
The HC allows one way flow only. Under normal forward flow, the valve opens as the higher inlet pressure lifts the inner valve assembly and the fluid in the upper chamber is discharged to the lower pressure, downstream side of the valve.
When pressure is reversed, the now higher downstream pressure is applied to the upper operating chamber as flow reversal occurs. The diaphragm / inner valve assembly moves down and the valve closes tightly.