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