A check valve in the vent inhibits the flow of fugitive gases to the vent and allows the escape of the fugitive gases to the vent if {HEAD ~ the pressure} of the fugitive gases exceeds {TAIL ~ a predetermined value} 
exceeds
A check valve in the vent inhibits the flow of fugitive gases to the vent and allows the escape of the fugitive gases to the vent if { HEAD ~ the pressure } of the fugitive gases exceeds { TAIL ~ a predetermined value }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL