Air tool overspeed shutoff device

Abstract

An overspeed shutoff device for use in a rotary pneumatic tool is disclosed. The device is operable to shut off air supply to the motor on failure of its governor to function properly in preventing overspeeding of the motor. The device includes a valve closing plate positioned in the path of air flow to the pneumatic motor, just upstream of an inlet port for passage of air into the motor. In normal operation of the tool the valve plate, which rotates with the motor drive shaft, is retained in a position spaced from the air inlet port by a locking mechanism engaging the drive shaft of the tool to prevent axial movement therealong. The plate locking device comprises a cantilever mounted spring wire in engagement with a groove in the drive shaft and a centrifugally responsive weight operably connected to disengage the wire from the groove in response to the attainment of a predetermined rotary speed. Upon failure of the main governor of the tool and consequent acceleration of the motor to such predetermined speed, the wire is disengaged from the shaft groove and the air pressure drop across the valve inlet port causes the closure plate to move toward and cover the inlet port, thereby stopping the flow of air to the motor.