An upper outlet permits {HEAD ~ the venting} of {TAIL ~ gases} that percolate from the liquid constituent, a backpressure valve disposed in communication therewith to maintain a positive pressure within the vessel 
An upper outlet permits { HEAD ~ the venting } of { TAIL ~ gases } that percolate from the liquid constituent , a backpressure valve disposed in communication therewith to maintain a positive pressure within the vessel
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH