Selective firing system

Claim 1

IN COMBINATION WITH A SEALED PERFORATING APPARATUS HAVING SEPARATE CHAMBERS EACH CONTAINING ELECTRICALLY ACTUATED EXPLOSIVE PERFORATING MEANS, SAID APPARATUS HAVING A BORE INTERCONNECTING SAID CHAMBERS, ELECTRICAL SWITCHING MEANS FOR ESTABLISHING AN ELECTRICAL CIRCUIT TO ONE OF SAID PERFORATING MEANS COMPRISING: A PISTON MEMBER HAVING ENLARGED AND REDUCED PORTIONS WITH SAID REDUCED PORTION BEING ARRANGED FOR TRAVEL IN SAID BORE BETWEEN SPACED LONGITUDINAL POSITIONS; FIRST AND SECOND ELECTRICAL CONTACTS OPERATIVELY ARRANGED TO BE OPEN IN ONE OF SAID PISTON POSITIONS AND TO BE CLOSED IN THE OTHER OF SAID POSITIONS; MEANS FOR FLUIDLY SEALING SAID REDUCED PISTON PORTION RELATIVE TO SAID BORE; MEANS RESTRAINING SAID PISTON MEMBER IN SAID ONE POSITION AND RESPONSIVE TO DYNAMIC EXPLOSIVE PRESSURES IN ONE OF SAID CHAMBERS AGAINST SAID ENLARGED PISTON PORTION TO RELEASE SAID PISTON MEMBER AND PERMIT TRAVEL OF SAID PISTON MEMBER TO SAID OTHER POSITION; AND MEANS PREVENTING RELEASE OF SAID RESTRAINING MEANS WHENEVER LIQUID FILLS SAID ONE CHAMBER INCLUDING FLOW RESTRICTION MEANS IN FLUID COMMUNICATION BETWEEN SAID ONE CHAMBER AND SAID BORE INTERMEDIATE OF SAID ENLARGED PISTON PORTION AND SEALING MEANS.