The vessel and the seal cover have respective surfaces that, when engaged, define a circumferential interior passage between {HEAD ~ the vessel} and {TAIL ~ the seal cover} 
The vessel and the seal cover have respective surfaces that , when engaged , define a circumferential interior passage between { HEAD ~ the vessel } and { TAIL ~ the seal cover }
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 TAIL TAIL TAIL TAIL TAIL TAIL TAIL