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