Variable reciprocating plunger pump

A reciprocating plunger pump having variable pumping modes is disclosed. A pump housing having an enclosed pump chamber provided with a valved inlet and a valved outlet is provided. A first plunger having a piston end extending into the pump housing and an outer end extending outside of the housing is driven in a reciprocal motion to produce a pumping action in the pump chamber. A second plunger having an inner end extending into the pump chamber and an outer end located out of the pump chamber is also mounted for reciprocal motion. The second plunger is removably attached to the first plunger. When the two plungers are attached together, a high pressure and low volume pumping of a fluid is achieved. When the two plungers are not attached together, a lower pressure and higher volume pumping of the fluid is achieved. Preferably, both plungers are substantially cylindrically shaped and the piston end of the first plunger is greater in diameter than the inner end of the second plunger. In order to attach the second plunger to the first plunger, a suitable screw projects from the second plunger and is threadably received in the first plunger.