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