The hole is preferably selectively exposed to a discharge pressure for {HEAD ~ a small portion} of {TAIL ~ the cycle}, and to an intermediate pressure for a second small portion of the cycle 
of
The hole is preferably selectively exposed to a discharge pressure for { HEAD ~ a small portion } of { TAIL ~ the cycle } , and to an intermediate pressure for a second small portion of the cycle
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH