Annulus pressure then acts against {HEAD ~ the bottom side} of {TAIL ~ piston} 40 and moves the mandrel up and opens the valve 
of
Annulus pressure then acts against { HEAD ~ the bottom side } of { TAIL ~ piston } 40 and moves the mandrel up and opens the valve
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH