a setting tool is provided for positioning in a subterranean wellbore . the tool carries a pre - charged , pressurized chamber , preferably filled with inert gas . a force - balanced piston assembly , with the piston chamber initially at atmospheric pressure , is in selective fluid communication with the pressurized chamber . a release mechanism , rupture disc , or valve is selectively operable to open the pressurized chamber and allow fluid flow to the piston chamber . the pressurized gas drives the piston which , in turn , drives a power rod for setting a downhole tool . preferably a flow restrictor is incorporated in the gas flow path to meter the fluid and control the setting speed . in a preferred embodiment , the pressurized chamber is opened by rupturing a disc . a pyrotechnic device , which qualifies as a non - explosive device and is triggered by a low - powered battery , drives a piercing member into and through the rupture disc .