Blasting cartridges

Claim 1

A REUSABLE BLASTING CARTRIDGE COMPRISING A SUBSTANTIALLY CYLINDRICAL HOUSING HAVING A MAIN CHAMBER FOR CONTAINING A CHARGE OF COMPRESSED GAS, MEANS AT ONE END FOR INTRODUCING GAS UNDER PRESSURE, AN ENCLOSED SECONDARY CHAMBER, A LATERAL OUTLET INTERMEDIATE THE ENDS OF THE HOUSING, A PRESSURE RESPONSIVE MAIN VALVE HAVING A BODY SLIDABLE IN SAID HOUSING BETWEEN THE MAIN CHAMBER AND THE SECONDARY CHAMBER AND NORMALLY POSITIONED TO SPAN AND SEAL SAID OUTLET, A PASSAGEWAY THROUGH THE VALVE BODY INTERCONNECTING THE CHAMBERS, AN INTERNAL ANNULAR RESTRICTTION IN THE HOUSING ADJACENT THE LATERAL OUTLET AND POSITIONED BETWEEN THE OUTLET AND THE GAS INLET, SAID VALVE BODY HAVING A GREATER DIAMETER THAN THE INTERNAL DIAMETER OF THE CONSTRICTION AND A NARROWED FORWARD PORTION ADAPTED FOR SEATING ON THE RESTRICTION IN SAID MAIN CHAMBER, SAID NARROWED FORWARD PORTION FORMING WITH SAID HOUSING AN ANNULAR OBTURATED CHAMBER BETWEEN THE RESTRICTION AND THE MAIN VALVE BODY, THE NARROWED FORWARD PORTION OF THE VALVE BODY FACING THE MAIN CHAMBER HAVING AN EFFECTIVE AREA LESS THAN THE EFFECTIVE AREA OF THE VALVE BODY IN THE SECONDARY CHAMBER, WHILE THE SUM OF THE EFFECTIVE AREAS OF THE NARROWED PORTION OF THE VALVE BODY AND THAT PORTION OF THE VALVE BODY WITHIN THE OBTURATED ANNULAR CHAMBER IS GREATER THAN THE EFFECTIVE AREA OF THE VALVE BODY IN THE SECONDARY CHAMBER, A CONTROL VALVE WITHIN THE MAIN VALVE BODY, SAID CONTROL VALVE BEING SOLELY RESPONSIVE TO PRESSURE WITHIN THE MAIN CHAMBER, A VENT WITHIN THE NARROWED FORWARD PORTION OF SAID MAIN VALVE BODY EXTENDING BETWEEN THE MAIN CHAMBER AND THE ANNULAR SEALED CHAMBER NORMALLY CLOSED BY THE CONTROL VALVE AND MEANS IN THE SECONDARY CHAMBER FOR RETURNING THE MAIN VALVE TO A POSITION SPANNING THE LATERAL OUTLET.