At the end of {HEAD ~ each piston}, a second camming surface is provided which engages {TAIL ~ the first camming surface} 
At the end of { HEAD ~ each piston } , a second camming surface is provided which engages { TAIL ~ the first camming surface }
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL