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