The HD1 series variable piston pumps for closed loop circuits are axial pistons pumps with swash plate design and through drive shaft on option. These pumps have been specifically designed for use in closed circuit hydrostatic transmissions. The delivery is proportional to the rotation speed and the swash plate angle. The delivery increases when swash plate’s angle of inclination increases from 0 to maximum position. Inverting the swash plate’s angle, the flow direction is inverted. The technical choices allow the new unit to operate at pressures up to of 400 bar [5800 psi].