Abstract: A hydraulically operated power transmission includes a hydraulic pump drivable by a power source, a hydraulic motor for driving a device, a primary oil passage leading from the hydraulic pump to the hydraulic motor, a secondary oil passage leading from the hydraulic motor to the hydraulic pump, a plurality of relief valves openable at higher and lower pressure levels, respectively, a shuttle valve for selectively connecting the relief valves to the primary and secondary oil passages in response to the difference between oil pressures in the primary and secondary oil passages, and a restriction disposed in an oil passageway extending from the primary oil passage through the shuttle valve to the relief valve openable at the lower pressure level, the restriction being located between the shuttle valve and the relief valve openable at the lower pressure level.