Patent ID: 7827961

Claim:
A pump for pumping a fluid, the pump comprising: a body defining a longitudinal bore; first and second inlets communicating with the bore; first and second outlets communicating with the bore; a plunger slidably mounted for reciprocation within the bore and configured to pump, by reciprocation of the plunger, fluid from the first inlet to the first outlet and from the second inlet to the second outlet; a piston slidably mounted within the bore and arranged to operate in a first, stationary mode, in which fluid may be pumped from the second inlet to the second outlet by the reciprocation of the plunger alone, and in a second, reciprocating mode, in which fluid may be pumped from the first inlet to the first outlet by the reciprocation of both the plunger and the piston; and a retainer for selectively holding the piston when in the first stationary mode.