Abstract: A pneumatic torque impulse wrench comprises a housing (10), a motor (15), a hydraulic impulse unit (20) including an inertia drive member (21) and intermittently coupling the motor (15) to an output shaft (18), a shut-off valve (23) controlling the pressure air supply to the motor (15), and an activating mechanism (25) arranged to shift the shut-off valve (23) from a fully open position to a closed position via one or more partly closed positions. An activating mechanism (25) for shifting the shut-off valve (23) comprises a retardation responsive inertia element (28) movably supported on the inertia drive member (21), and a trip element (24) displaceable by the inertia element (28) and arranged to initially support the shut-off valve (23) in a fully open position during a screw joint tightening process and in succeeding one or more partly open positions for obtaining a power reduction of the motor (15) when approaching a target torque level.

Abstract: The present invention relates to a back-flow preventing valve (1) offering low resistance to fluid flow (AF) through the valve in an open position thereof and yet enabling secure closing of the valve. The reduced resistance to flow is achieved by arranging vanes (3, 3′, 3″) of the valve so that in said open position they are essentially balanced with regard to the force of gravity and do not significantly impede the airflow, neither with regard to the pressure drop caused by the valve nor with regard to an undesirable deflection of said airflow. Leaving said open position the vanes are increasingly urged towards their closed position by the force of gravity. Specifically, this is accomplished by inclining the pivot axes (A) of the vanes (3, 3′, 3″) against the general direction of flow (AF) through the valve (1).