The cell within which {HEAD ~ the vent} is located begins to drain fluid or {TAIL ~ gas} and a pressure differential occurs between the two cells 
The cell within which { HEAD ~ the vent } is located begins to drain fluid or { TAIL ~ gas } and a pressure differential occurs between the two cells
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH