The water flow in the pump outlet pipe suddenly changes due to sudden changes in valve opening, valve closing, and pump stop, which cause a sudden change in the flow velocity in the pipe, which causes a change in momentum per unit time, which will inevitably generate a corresponding inertial force, which will cause pressure in the pipe. The alternation phenomenon of sudden rise and sudden fall. This phenomenon that the velocity and pressure of water flow change with time and position is called water hammer (or water hammer).

When the pump outlet is equipped with a check valve (return valve), it will be closed immediately to prevent the high-pressure water from flowing back into the pump. If the water pump outlet is not equipped with a check valve (return valve), the high-pressure water will flow back into the water pump in reverse, and the impeller of the water pump will reverse under the impact of high-pressure water. The impeller bears the impact load of high-pressure water, which may loosen or damage the impeller or other parts in severe cases; reduce the water pressure of the main pipe and the water level, etc., affecting safe operation.

Selection of pump outlet check valve (return valve)

• For pipelines with a smaller diameter at the outlet of the pump, that is, when DN<50mm, lift check valves (return valves) should be selected.
• For the pipeline with the diameter of the pump outlet pipeline DN ≥ 50mm, the swing check valve (return valve) should be selected

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