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