What is a check valve? Do I need a check valve?
A check valve is a valve that is used to prevent backflow in a piping system. The pressure of the liquid passing through the pipe will open the valve, while any reversal of flow will close the valve. The check valve will help your water system maintain pressure when the pump shuts off and also prevent backspin, upthrust, and water hammer.
It is recommended that at least one check be installed in all submersible well pump installations. Many well pumps have built-in check valves. Even if a pump does have a built-in check valve, we recommend that a check valve be installed in the discharge line within 25 feet of the pump and below the draw down level of the water supply. Although installers have different opinions, in deep wells we recommend that check valves be installed every 200 feet to distribute the weight on each valve.
What type of check valve do I want? Swing type check valves should never be used in a submersible well pump installation. Swing type check valves have a slower reaction time and can cause water hammer. Spring loaded check valves should be used as they close quickly and thus help prevent water hammer. It should be properly sized to meet the pump’s flow and pressure conditions. The check valves pressure rating must exceed the maximum pressure of the pump.
Backspin, upthrust, and water hammer can lead to early pump or motor failure.
Backspin. When the motor stops, water in the drop pipe can flow down the discharge pipe when there is no check valve or a failed check valve. The flow can cause the pump to rotate in the reverse direction. If the pump starts while it is backspinning, it can cause an excessive force that can break the pump shaft, cause impeller damage, or cause bearing damage.
Upthrust. With a failed check valve or no check valve, the pump will start with zero head pressure. When there is low or no pressure the impellers will “float” up and wear on the diffusers above. This repeated wear can cause premature failure of both the pump and the motor.
Water Hammer. A failed or leaking check valve can cause a vacuum in the discharge piping. When the pump starts, water moving at a very high velocity fills the void and strikes the stationary water in the piping above it, causing a hydraulic shock. The shock can split pipes, break joints, or damage the pump and motor.