When the float switch signals the pump to start, it forces the pump to push water through the valve, and out through the discharge pipe. When the water level drops, the float switch signals the pump to stop, stopping the water. Gravity then causes the water that is in the discharge pipe to drain back into the pit.
The check valve is there to prevent the pump from having to re-pump that volume of water over again. Eliminating this issue will save on electricity costs.
Short cycling of a sump means that the pump turns on and off too quickly or too frequently. Short cycling causes the pump motor to run hotter. Heat is an enemy of electric motors and can shorten the life of a sump pump significantly. By installing a check valve, it will reduce the risk of short cycling, especially in smaller size sump basins. A check valve will extend the life of the sump pump, and save you money.
The most suitable location for a sump pump check valve is between 8″ up from the pumps discharge to approximately 12″ above floor level. Installation above the floor level is convenient for easy inspection, servicing, or replacement of the valve. You want to install a check valve 6″ above the pump discharge when installed down inside the sump basin to allow for the drilling of air release or weep holes to protect against air lock for sump pumps that do not have a built-in air lock prevention system.
Always refer to the sump pump manufacturers installation instructions.
Installing the sump check valve down in the sump basin below the cover can reduce the noise caused by water hammer if a standard gravity closing valve is installed, however, making inspections and servicing is not not nearly as convenient.
Improper Installation or Not Installing one at all
Not having a sump pump check valve installed causes the water in the discharge pipe to empty back into the sump pump pit. This makes the water level in the sump pit rise and a high water level can cause the pump to run more often, increasing your energy costs.
If the check valve is installed in the incorrect spot such as too high up on the discharge pipe, the pump will empty the pit during the run cycle but when it shuts off, the water below the check valve will drain back into the basin causing the water level to rise very quickly. When that happens, it will trigger the float switch to start the pump again right away, eventually wearing out your pump prematurely.
Sump pump check valves are available in three basic types, shown in the pictures below. Each type is available in a variety of sizes and connection types.