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