{HEAD ~ The chamber} is sealed upon {TAIL ~ purging} of all the air and is maintained in a pressurized state for a period of time 
{ HEAD ~ The chamber } is sealed upon { TAIL ~ purging } of all the air and is maintained in a pressurized state for a period of time
HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH