Pressure actuated running tool

A running tool A for preventing premature release of a tool 88, is run into the wellbore on a line 14. At the lower end of said running tool A grippers 60 releasably locate said tool 88. A piston 64 attached to the grippers 60 has lower end exposed to the wellbore pressure via. a port (100, fig. 4b), while its upper end is selectivly exposed to the wellbore pressure by movement of body 48 relative to port 70, the movement being dependant on the weight applied by the tool 88. An annular cavity 34 is pre-pressurised at the surface to a pressure just below that of the wellbore pressure at the deployment location of the tool 88. At the deployment depth, floating piston 44 is displaced upwards due to the pressure differential acting upon said piston 44, resulting from the precharged pressure acting upon said pistons upper end and the wellbore pressure acting upon said pistons lower end. As the piston 44 has been displaced the piston 64 and grippers 60 are urged upwards, forcing said grippers 60 outwards (as fig. 5b) releasing the tool.