During a switching off operation, the moveable contact member moves out of the arcing chamber and {HEAD ~ quenching gas} flows from the accumulator space into the expansion space, through {TAIL ~ the arcing chamber}, i.e. the nozzle 
flows through
During a switching off operation , the moveable contact member moves out of the arcing chamber and { HEAD ~ quenching gas } flows from the accumulator space into the expansion space , through { TAIL ~ the arcing chamber } , i.e. the nozzle
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL OTH OTH OTH OTH OTH OTH OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH