Non-return valve (NRV) allows a medium to flow in only one direction. Non return valve is mainly used to restrict the flow of a fluid in reverse direction so that a fluid flows in the right direction where pressure conditions may otherwise cause reversed flow. Centrifugal pump always requires a NRV.
The closure of non-return valves can cause water hammer. This occurs when water flowing through the pipes is suddenly forced to stop or change direction, i.e; the flowrate of fluid changes rapidly. This surge flow can cause very high pressures in pipes, very high forces on pipe supports, and even sudden reversals of flow. It can cause pipe burst, damaged supports, and leakage at joints. Sometimes dampers are put to harmonize dynamic behavior of disc. The flow through the non-return valve causes a relatively large pressure drop, which has to be taken into account when designing the system. Depending on system requirement, there can be a variety of Non-return valve. Each has got typical advantages and disadvantages too. The designer has to choose the optimum product to suit the system best.