Hydrostatic pressure responsive bypass safety switch

A safety switch apparatus for use with an explosive well tool to prevent accidental or premature firing thereof, comprising:

• a hollow conductive body having one end adapted to the coupled to an explosive well tool and another end adapted to be coupled to a cable head on the end of an armored electric cable;
• a conductor rod extending axially of said body and adapted to conduct electric current from said cable to said well tool to fire the same;
• said body having a radially arranged bore extending through a wall thereof;
• an elongated, cylindrical, pressure operated contact member mounted for transverse movement in said bore between a first position and a second position, said contact member having an opening through which said conductor rod extends, a wall surface of said opening engaging said conductor rod in said first position and being disengaged therefrom in said second position;
• means for biasing said contact member toward said first position with a preselected pressure;
• and means for subjecting said contact member to the hydrostatic pressure in a well bore, so that a predetermined level of said hydrostatic pressure will overbalance said biasing means and shift said contact member to said second position.

A safety switch system for use with an explosive well tool, comprising;

• a hollow conductive body;
• conductor means extending through said body for conducting electric current to said well tool to fire the same;
• piston means on said body having contact means and movable between a first position where said contact means engages said conductor means to ground said conductor means to said body, and a second position where said contact means is disengaged from said conductor means;
• and external spring means for biasing said piston means toward said first position, said piston means being responsive to hydrostatic pressure in a well bore for overbalancing the bias of said spring means and moving said contact means out of engagement with said conductor means.

A safety switch system for use with an explosive well tool, comprising;

• a body having insulated conductor means therein, said conductor means having a bare surface between its ends;
• piston means on said body and having a contact surface movable between a first position where said contact surface engages said bare surface to ground said conductor means to said body and a second position where said surfaces are out of engagement;
• spring means for biasing said piston means toward said first position, said piston means being responsive to hydrostatic pressure in a well bore for overbalancing said spring means and moving said piston means to said second position;
• and a contact member on said body movable between a first position where a contact surface thereon engages said bare surface to provide an additional ground of said conductor means to said body and a second position where said contact surface is out of engagement with said bare surface, said contact member being manually operated between its first and second positions.

A method of arming an explosive well tool only after it has been lowered past a predetermined depth in a fluid-filled well bore on an armored electric cable, comprising the steps of:

• providing a normally closed switch at the upper end of said well tool that provides a path whereby electric current in said cable can be shorted to ground;
• biasing said switch to said normally closed position with a predetermined bias pressure;
• opposing said predetermined bias pressure with increasing hydrostatic pressure as the tool is lowered into the well;
• and opening said switch when said hydrostatic pressure overbalances said predetermined bias pressure to eliminate the short to ground.