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