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.

The foot valve is placed at the bottom of the intake water line in the well; since your jet pump is above ground, it's a physically separate component.

The check valve is a one-way valve that lets water flow up from the well and into the well piping. The spring loaded check valve closes when the well pump stops pumping.

Foot valve check valve portion (C) Daniel FriedmanClosing 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.

Foot Valve Clearance from Bottom shows that the well piping and foot valve are inserted into the well some distance from the very bottom of the well (inches to a few feet). We need this clearance to reduce the tendency of the well pump to pick up mud and debris from the bottom of the well.