{HEAD ~ Each hole} is open for {TAIL ~ a small portion} of the operational cycle to selectively tap an intermediate and discharge pressure to the back pressure chamber 
is open for
{ HEAD ~ Each hole } is open for { TAIL ~ a small portion } of the operational cycle to selectively tap an intermediate and discharge pressure to the back pressure chamber
HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH