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