Under pump/in-line check valves are designed to be installed directly in the inlet of the dispenser pumping unit to maintain prime on a suction system fuel line. The under pump/in-line check valve can also be used in a pressurized system at the submersible pump outlet to hold product in the line. Cast-in Hex for sturdy wrenching surface. NPT threads on both ends are designed to receive female threaded product lines. Pressure relief models relieve thermal expansion in the pumping unit, reducing the chance of vapor lock.