Sauer Danfoss MF, SMF Hydraulic Piston Motor And Concrete Mixer Motor And Eaton HHD Concrete Mixer Hydrostatic Fixed Motor  SMF20 SMF21 SMF22 SMF23 SMF24 swash plate in closed circuit operation and are intendent for closed circuit operation. The output speed is propor tional to the flow rate of 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 (output) shaft rotation depends upon which port the fluid enters the motor.