A check valve is a one-way flow device that permits water movement in only one direction through a pipe while preventing reverse flow or backflow. These simple, reliable valves use internal flapper mechanisms, spring-loaded cones, or ball designs that open freely under forward pressure and snap shut when flow tries to reverse. Check valves are fundamental safety components in HVAC and plumbing systems.
Types and Pressure Drop
Swing check valves use a hinged flapper and are suitable for low-velocity applications with minimal pressure loss. Spring-loaded check valves provide better sealing and prevent water hammer but add 2-5 PSI pressure drop. Ball check valves offer compact sizing for tight spaces. Pressure ratings range from 125 to 300 PSI depending on design and materials.
HVAC System Uses
Check valves prevent reverse flow in boiler return lines, preventing hot water from flowing backward through cooler branches. Heat pump systems use check valves in refrigerant lines to isolate components during idle periods. They protect expansion tanks from backpressure and prevent contamination where multiple water sources connect.
Selection Criteria
Valve size must match pipe diameter. Orientation matters for swing-type models, which must be installed in horizontal pipes. Pressure ratings must exceed maximum system pressure by 20 percent. Regular inspection prevents sticking from sediment accumulation that causes backflow.