Common rail fuel pump with combined discharge and overpressure relief valves

A high pressure single piston fuel pump having a housing, a pumping chamber within the housing, a piston with one end in the pumping chamber and another end outside the housing, which piston reciprocates between a retracting motion during which fuel is delivered to the pumping chamber and a pumping motion during which the piston pressurizes fuel in the pumping chamber, a discharge check valve between the pumping chamber and a pressurized common rail fuel reservoir, and a pressure relief valve between the common rail fuel reservoir and the pumping chamber, wherein:

• the discharge check valve and the pressure relief valve are contained within a single fitting assembly affixed at the housing;
• the fitting assembly extends longitudinally along a flow axis, having coaxially aligned first and second flow passages at respective first and second ends of the fitting assembly;
• the first flow passage is in fluid communication with the pumping chamber and provides an inlet to the discharge check valve and an outlet from the pressure relief valve;
• the second flow passage is in fluid communication with the common rail fuel reservoir and provides an outlet from the discharge check valve and an inlet to the pressure relief valve;
• and
• a unitary valve seat member is situated within the fitting assembly between the first and second flow passages, having a first valve seat for the check valve coaxially aligned with a distinct second valve seat for the pressure relief valve.