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Check valves play an important role in controlling the flow of fluids in a pumping application, but a water well application depends on check valves even more. Backflow prevention is the most common use of check valves, particularly in a system that is pressurized by a pump. Controlling backflow is critical in a well application for several more reasons.

 

Many submersible pumps have either integral or external check valves built into or on the pump itself. This is for the protection of the pump and attached motor. If no check valves are on the discharge of the pump, the backflow of the fluid can spin the pump backwards. The reversal may cause damage in some pump ends depending on the construction and any threaded parts could become loose.

 

Perhaps, the bigger issue with back spin relates to the motor. Submersible motors typically have a Kingsbury type thrust bearing, which supports the weight of the pump shaft combined with the column of water in the pipe. The design of this bearing allows it to be lubricated when operating at or above the minimum speed.

 

When water backflows through the pump the impellers tend to turn which also turns the motor, but at low rpms. At low speeds the thrust bearing is not lubricated and tends to grind the polished surfaces. This causes abrasive particles in the motor, and a drop in the shaft. This will cause impellers to drag below the set clearances and damage results in both the motor and pump end.

 

Because of the dynamics of a submersible pump system, check valves should be of a design special to a water system. It is important that check valves be spring loaded “non slam” type. A swing check for instance will slam shut and then bounce. This causes the column of water to also bounce and damage the motor thrust bearing.

 

In deep settings, more than one of the same model valve may be required to minimize the bounce since the water column will be much heavier.

 

The number of check valves is usually determined by the length of column pipe. Generally, motor and valve companies agree that one valve per 200 feet of column is the best practice. This is in addition to the check valve within the pump since its purpose is to protect against any backflow. Ideally, the first check valve should be within 21 feet of the pump.

 

Staging others is typically 200 feet apart. When possible, try to keep the top check valve under the static level. This will ensure that a leak below the top valve will only allow water to be sucked into the pipe, not air.

 

A check valve should also be placed near the water storage such as a tower or tank. Most valve companies offer a globe style or wafer check with a similar poppet movement as the line checks which also prevents bounce in the water column.

 

A good installation with a proper check valve system eliminates potential damage to the pump assembly and provides long service. Valving should be considered in every pump installation.