{HEAD ~ the second valve} is operable only between a valve open position and {TAIL ~ a valve closed position} 
is operable between
{ HEAD ~ the second valve } is operable only between a valve open position and { TAIL ~ a valve closed position }
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL OTH REL OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL