In a variable capacity pump with an inlet port and a discharge outlet adapted for connection to a nozzle, a cylinder within the pump body having a casing and a pump stator slidably mounted in the cylinder and receiving a vaned rotor for receiving fluid from said inlet and discharging to said outlet; the improvement which includes a delivery chamber receiving said pumped fluid with a cut off valve opening. Said opening includes a valve seat with a soft valve in one end of the movable stator normally engaging said seat. A spring retainer is normally spaced outwardly of one end of the stator and a weak air release spring is interposed between said retainer and said stator. A discharge pressure spring is interposed between the pump body and said retainer, normally holding the retainer during initial movement of the stator towards and into engagement with the retainer so that initial low pressure air delivered to said chamber lifts the soft valve from said seat for delivery to said nozzle. Solid liquid subsequently pumped to said chamber of progressively increasing pressure causes the stator to move further radially outward against the action of said discharge pressure spring further opening said valve to reach an equilibrium of volume of pumped liquid delivered to said nozzle. The improved pump includes opposed pairs of intake and outlet grooves upon opposite sides of the stator registerable with corresponding pairs of intake and discharge ports extending through the inner and outer walls of the pump cylinder together with opposed bosses upon opposite sides of said stator normally closing one of each pair of intake and discharge ports whereby, the stator is reversible face to face, depending upon the direction of rotation of the rotor. An improved drive shaft seal is incorporated into the pump body which includes a stationary seal element on the body and a rotative seal element engageable therewith and connected with said drive shaft.