into check valve 88 engaging check ball 89 and compressing check spring 92 if gas control valve 33 is in the open position inert gas passes into lower chamber 40 through check valve 88 and into block annulus 93 gas passes from block annulus 93 into jumper 90 via inlet passages 94 which are in fluid communication with annular space 96 by way of outlets 97 gas then passes from annular space 96 into passages 104 then into annular space 101 of cable 100 when jumper 90 is removed from receptacle 82 tip 91 disengages check ball 89 and check spring 92 biases check ball 89 to close off check valve 88 as shown in fig3 b and 3c jumper 90 is preferably composed of two pieces taper 98 which includes inlet passages 94 tip 91 and outlets 97 and connector 99 which includes passages 104 and is preferably threadably connected to taper 98 by way of threads 103 conducting wire 102 is preferably solder connected to connector 99 jumper 90 is preferably held in place by friction in a particularly preferred embodiment a standard morse zero taper in both receptacle 82 and taper 98 and proper sizing of the diameter of receptacle opening 105 provide a friction fit when jumper 90 is inserted in receptacle 82 o ring 106 in jumper 90 provides a seal to restrain the flow of gas from block annulus 96 to the exterior of lower chamber 40 when jumper 90 is inserted into receptacle 82 both blocks 44a f and jumper 90 are preferably composed of a conducting material to allow current to.