Abstract: A double acting pump includes an elongated thin walled hollow barrel, having an inlet end and a head end, and an elongated hollow plunger slidably received in said barrel and forming with its inner surface an annular space. A two piece detachable fitting includes one part on the head end of the barrel, and a mating part with a seal between one end of the barrel and the outer surface of the plunger. A valve assembly and seal is mounted on the inlet end of the plunger, with that seal engaging the interior of said plunger. A nozzle is mounted on the discharge end of the plunger. A two piece inlet fitting includes one part on the inlet end of the barrel, a mating detachable part having an inlet valve seat, and a check valve captured between the parts of the inlet fitting and cooperating with the seat to allow flow into the barrel. A filter piece is supported in the detachable part of the inlet fitting and also functions to capture the check valve between the seat and the filter piece.