A Vickers Model 25M (65) vane motor was chosen for the comparison. This motor is rated for 3000 rpm at 2500 psi maximum pressure. It has a displacement of 4.19 in3/rev. Efficiencies were calculated for a 35 GPM input flow.
As shown in Fig. 5.4, the torque efficiency for this design is higher than for the gear motor, and it is relatively constant over the pressure range 500 to 2500 psi. Overall efficiency for the motor tends to be a little higher than for a comparable vane pump .
Vane motors are available with two displacement settings. These motors have two rotors. A given flow directed to only one of the rotors will produce twice the speed but only half the torque. When maximum torque is needed, the input flow is sent to both rotors, thus doubling the displacement and doubling the output torque. Speed is, of course, halved. The operator adjusts a valve on the outside of the motor to switch from low-speed, hightorque (two rotors) to the high-speed, low-torque (one rotor) configuration. One application for such a design is a wheel motor for an agricultural machine. The machine needs low speed and high torque for field operations, and the operator shifts to high speed, low torque for road travel between fields.
