Spring loaded, stem or cage poppet style check valves should be used with submersible pumps. They are designed to close quickly as the water flow stops and begins to move in a reverse direction. Swing type check valves should not be used. When tile pump stops, there is a sudden reversal of flow before the swing check closes, causing a sudden change in tile velocity of tile water and a water hammer.
It is important to choose and install a check valve correctly to help ensure a trouble-free water system. It should be properly sized to the pump's flow and pressure conditions. Prior to installing a check valve, be certain its mechanism is operating properly. Install the valve with dye-imprinted flow arrow in the correct direction.
Normally, the first check valve should be installed on or directly above the pump. If you have a slow producing well that pumps a little air from time to time, the first check should be installed 5 feet or so above the pump to allow the pump to purge itself of air more easily. A check valve should never be installed more then 25 feet above the lowest pumping level in the well. For deeper settings, it is recommended that a line check valve be installed every 200 feet. Another check valve may be installed in tile horizontal piping at tile surface or just below the well seal or pitless adapter as required by local codes. There is risk of water hammer in the upper check valve if the lower check valve fails. (See diagram)
Properly located and operating check valves hold water pressure in the system when the pump stops. They also extend the life of and assist in the smooth operation of tile water system by preventing backspin, up-thrust and water hammer.
Backspin - With no check valve, or if the check valve fails, the water in the drop pipe and the water in the system will flow back down the drop pipe when tile motor stops. This can cause the pump to rotate in a reverse direction as the water flows back down the pipe. If the motor were started while this is happening, a heavy strain would be placed on the pump-motor assembly, possibly causing the pump shaft to break or motor thrust bearing damage.
Upthrust - With no check valve, or with a leaking check valve, the pump starts each time under zero head conditions. With most pumps, this causes an upthrust on the impellers-shaft assembly in the pump. This upward movement carries across the pump-motor coupling and creates an upthrust condition in the motor. Repeated upthrust at each start can cause premature wear and failure of either- or both- the tile pump and the motor.
Water Hammer - Water flowing through a piping system has kinetic energy (weight and velocity). When the pumping stops, the water continues to move. Its energy must be absorbed in some way. A rapid absorption of energy can cause noise and/or damage. This is called water hammer, or shock. This shock can split pipes, break joints and damage the pump. Water hammer varies in intensity depending on the velocity with which the water is traveling when the pump shuts off.
The use of quality spring loaded check valves is an important part of providing your customer with a water system that will perform like new for years. I'd like to thank Maass Midwest in Huntley, Ill., for its input on this article. Next time I will show how to build a pump test station and provide a listing of suppliers of the bits and pieces you will need.