Abstract

A pneumatic power tool for tightening screw joints includes a primary motor 11 for the high speed running down sequence and a secondary motor 12 for the high torque final tightening sequence. The tool includes a coupling gearing 18 providing a high ratio gearing for the secondary motor 12, a gearing of a substantially lower ratio for the primary motor 11 and a one-way clutch 30 by which the secondary motor 12 is automatically engaged at decreasing tightening speed. An air supply valve 33 is employed to substantially reduce the air consumption of the tool by keeping the air supply to the secondary motor 12 shut off until a certain degree of tightness in the joint is obtained, after the valve 33 is opened and the secondary motor 12 is energized.A reduction gearing 19 is supported in a casing 90 which is rotatively connected to the tool housing 10 and provided with a laterally extending torque reaction bar 92. An arresting mechanism is employed to prevent rotation between the tool housing 10 and the gear casing 90 when the tool is in operation. Balls 96,97 are arranged in the housing 10 to lock either the gear casing 90 or the throttle valve trigger 16 against movement relative to the tool housing 10 by engaging either one of a row of notches 93 on the gear casing 90 or a groove on the trigger stem 94.