Axial piston variable displacement pumps, Series 20, are of swash plate design with variable flow capability uitable for hydrostatic transmissions with closed circuit. The flow rate is in proportional relation with the input pump speed and continuously variable displacement, which, in turn, is determined by the swash plate angle and is adjustable between zero and maximum value of the displacement. Flow direction is reversed by a tilting of the swash plate to the opposite side of the neutral or zero displacement position. Frame sizes 20 - 23