A hydrostatic transmissions consists of a hydraulic pump and motor, typically used as the main   drive system on modern construction and many other industrial equipments.

Axial piston variable displacement pumps are of swash plate construction with variable flow capability suitable for hydrostatic transmissions with closed loop circuit. The flow rate is proportional to the pump´s driven speed and displacement which in turn is determined by the swash plate angle. The latter is infinitely adjustable between zero and maximum displacement. Flow direction is reverted  by tilting the swash plate to the opposite direction side of the neutral or zero displacement position.

Axial piston fixed displacement motors are of swash plate construction with preset displacement, and are intended for closed circuit, too. The output speed is proportional to the input fluid. The output torque is proportional to the differential between high and low pressure sides of the fluid circuit. The direction of motor shaft rotation depends upon which port of the fluid enters to the motor.