Hydro-impulse screwing device

A hydro-impulse screwing device comprises a rotary drive motor, a power source for the motor, a drive shaft, a pulsating hydraulic drive connecting the motor to the shaft and a power cut-off for the motor. The load at which the power cut-off functions is adjustable. The tool has a borehole extending through the length of the shaft, a conduit for conducting hydraulic fluid from the drive to the borehole, a valve in the borehole movable from a closed position to an open position in response to hydraulic pressure corresponding to a predetermined load to allow hydraulic pressure from the drive to actuate the power cut-off, a biassing element in the borehole for biassing the valve toward a closed position against the hydraulic pressure, wherein the force of the biassing element is adjusted at the end of the drive shaft to change the load at which the power cut-off operates.