{HEAD ~ The position} of {TAIL ~ the vent} can be moved to either side of the piston 
of
{ HEAD ~ The position } of { TAIL ~ the vent } can be moved to either side of the piston
HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH