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Non-Return Valve (NRV) or Check Valve allows a medium to flow in only one direction. A NRV/Check Valve is fitted to ensure that a medium flows through a pipe in the right direction, where pressure conditions may otherwise cause reversed flow.
NRV’s/Check Valves can be fitted to ensure that a medium flows through a pipe in the right direction, where pressure conditions may otherwise cause reversed flow. A NRV/Check Valve allows a medium to flow in only one direction. The flow through the non-return valve causes a relatively large pressure drop, which has to be taken into account when designing the system.
There are different types of NRV/Check Valves, such as spring-loaded, swing type, and clapper type valves.
All valves are designed to meet a designated internal permissible leak rate standard (FCI/ANSI). There are six (6) permissible leak rates or Classes numbered 1 through VI. The higher the leak rate number, the lower permissible internal leak rate.
Identifying the permissible internal leak rate for a valve has to be one of the top priorities when choosing the correct valve. A valve with a high leak rate, will cause excessive wear. The valves with a high leak rate will internally pass more medium and result in premature valve failure.
There are six different seat leakage classifications as defined by ANSI FCI 70-2.