Foot valves work by ensuring that the water in a well pump only flows in one direction. Foot valves are a type of check valve, but they differ in that the flow area is larger in size than the rest of the pipe. This limits the amount of head loss in the pumping system.
The design of foot valves varies from one manufacturer to the next, but most work without springs or similar items. A semi-flexible rubber flap creates the valve. The valve is designed so that it only flexes in one direction. This way, when water pushes the flap in the desired direction, the flap yields easily. However, when the pressure starts to push in the other direction, the flap slams shut and resists the flow of water. Often, a wire or metal set of supports are attached to the valve to ensure it keeps its shape and withstands the sometimes considerable amount of pressure.
Foot valves are often installed in conjunction with gaskets, O-rings or flanges that help to keep the pipeline watertight. If the foot valve contains a hump or rounded portion of the housing, it should be placed in the uppermost position to ensure that the valve works properly.