A
pneumatic impact wrench. This device
is characterized in the improvement
of the torque controlling mechanism
incorporated therein, said mechanism
comprising a torsion bar, a spindle
case, a fluid element, and valves, holes
and passages all functioning in close
linkage with each other thereby enabling
execution of the torque control and
even change of the torque control value
precisely. In this mechanism, an air
motor driving this device is brought
to a halt automatically as the result
of closing of a main valve in relation
to the operation of said fluid element,
said operation of said fluid element
being available from air pressure change
caused by the closing or narrowing of
an air exhausting hole taking place
in compliance with twisting of said
torsion bar under its partially rolling
effect at the rear portion thereof,
said torsion bar fixing to said spindle
case at their forward portions at this
time being imparted with a rotation-suspending
resistance thereto at their fixing portion.
This invention is further advantageous
in that conventionally used automated
valves can be dispensed with besides
simplification of circuits being available
in the above-mentioned mechanism.