thereon through a bearing 64 suitable seals are provided between unlocking piston 62 cylinder 17 and cylinder head 18 to seal the unlocking chamber 60 the unlocking piston 62 moves from the locking position fig2 to the unlocking position fig2 a in response to abatement of locking or closing fluid pressure on inlet 24a and introduction of opening or unlocking fluid pressure in the cylinder 17 from inlet conduit 24b through the conduit 50 stinger 52 and conduit 58 which convey such pressure to the unlocking chamber 60 as the piston 62 moves to the unlocking position the force of springs 40 is overcome and movable clutch plate 38 is moved inwardly to a position fig2 a where a gap 66 is present and there is no engagement between the ratchet teeth 38a and 42a with the ratchet teeth 38a and 42a out of engagement with each other locking action between the lock nut 30 and body of the blowout preventer is removed and the threaded surface 26a of the tail shaft 26 is permitted to pass rearwardly through the surface of the lock nut 30 with the lock nut 30 and clutch plate 38 rotating in the reverse direction to the arrow 32 fig3 it should be understood that a lock l is provided for the left hand ram r as viewed in fig1 in the same manner as the lock l discussed above for the right hand ram r in fig2 in the operation of the blowout preventer b with the lock l when it is desired to move the ram r inwardly from the.