slipper pads bear against the swash plate face and the plungers are driven in and out axially for each revolution of the rotor. For one direction of tilt ports on one side of the horizontal center line become suction and on the other side of this center line become discharge. For the opposite direction of tilt the direction of flow is reversed. the quantity of discharge depends on the angle of tilt.In mid-position no relative movement exists between piston and end plate and no pumping action takes place