Abstract: A reciprocating priming piston pump is provided with a piston check valve which provides improved performance by minimizing the pressure drop there through. A dog-bone shaped seat is slideably located inside a piston which in turn slides inside the cylinder of the pump. The piston is restrained at one end by seating upon the valve seat and its outer end by contact with the displacement rod. Rounded surfaces on the valve seat contribute to smooth flow and a slotted guide fingers in the upper end of the piston allow ample flow into the upper chamber from the lower chamber.