Abstract: An improved rotary fluid pressure device is provided of the type especially suited for operation at relatively low speed. The device includes a gerotor gear set (13) having a star (27) which orbits and rotates, an output shaft (47) and a main drive shaft (51) to transmit rotation of the star to the output shaft. The valving comprises a spool valve member (49) defining axial ports (65) and (67) connected to the inlet and outlet, respectively, and stationary ports (41) communicating with the gerotor volume chambers. The stationary ports (41) have a port width W.sub.1 and the axial ports (65) and (67) have port widths W.sub.2 which is narrower than W.sub.1 and is selected such that the measured maximum cross-port leakage rate is approximately equal to the minimum rate. Because the cross-port leakage is kept constant, the flow to the gerotor is constant, resulting in optimized low-speed operation of the motor.