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