At a hot water heating system a heating system back flow preventer check valve is used to keep hot, high pressure water in the hydronic heating system from flowing backwards through a boiler water feed line into the building water supply - a sanitation concern.
Simply put, a check valve allows flow in one direction and automatically prevents back flow (reverse flow) when fluid in the line reverses direction. They are one of the few self-automated valves that do not require assistance to open and close
Flow-control valves include simple orifices to sophisticated closed-loop electrohydraulic valves that automatically adjust to variations in pressure and temperature. The purpose of flow control in a hydraulic system is to regulate speed. ... Flow rate also determines rate of energy transfer at any given pressure.