a valve seal disposed on {HEAD ~ said plunger} in {TAIL ~ the vicinity} of said downstream end thereof; and 
in
a valve seal disposed on { HEAD ~ said plunger } in { TAIL ~ the vicinity } of said downstream end thereof ; and
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH