Check Valves
Check valves prevent fluids (liquids or gasses) from flowing in the wrong direction. They are typically in a hose or channel and make it hard for the fluid to flow in one direction but easy to flow in the opposite direction. Check valves occur in nature as well as in technology; for instance, there are check valves in the arteries in our legs so that muscle action tends to squeeze the blood up toward the heart instead of down toward the feet. Check valves keep well water flowing up instead of down and the water in water intake systems flowing out of the lake instead of into the lake.
Foot Valves
Foot valves are check valves that make sure that the pump is always primed. If the pump is shut off, the foot valve makes sure that there is enough fluid in the pump to insure that it starts up again. This is especially important for pumps that are not easy to manually prime. In a well, the foot valve will be between the water surface and the pump. In a water intake system the foot valve will be at the end of the water intake line. A foot valve is basically a check valve combined with an inlet strainer. The strainer prevents picking up large debris that could clog or jam the foot valve in its open position (or that might damage the water pump itself).
The foot valve prevents water from flowing backwards out of the jet pump and well piping back into the well when the jet pump stops operating. Foot valves are also used on deep well installations to help protect against loss of prime in the well piping system. Without a working foot valve, a shallow well jet pump is likely to lose prime and will stop working properly, risking loss of water supply to the building and even damage to the pump itself.
Pumps
Pumps move fluids around. Typically, pumps move one "chunk" of a fluid across the pump, and the vacuum that this creates in the fluid is replaced by more fluid moving into the pump. The pump then transfers this new chunk, and the process starts all over again. It is kind of like eating--only in reverse. Pumps work by moving the fluid one bite at a time--each new bite pulling in the next.
The spring loaded check valve closes when the well pump stops pumping.
Closing the check valve prevents water in the well piping from falling backwards into the well when the pump has stopped running. We need this function to keep the well piping and water pump filled with water - otherwise the well pump may lose prime, leading to loss of water in the building.
If the well piping foot valve is leaky and water runs back into the well we increase the wear on the water pump as it has to run more often, and pretty soon the water pump will lose its prime (water inside the pump mechanism) and it may be unable to retrieve any more water from the well whatsoever.
When a shallow well appears to have "run dry" one of the first things to check is whether or not the foot valve needs to be replaced.
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