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