Down-hole blow-out preventers

DETAILED DESCRIPTION I claim: 1.
A down-hole blow-out preventer of the kind having means for connection into a drill string for use therewith in a bore hole, said blow-out preventer comprising: a housing formed with a bore extending through said housing for the passage therethrough of drilling fluid; means for connecting said housing into a drill string so that the bore of the housing communicates with the bore of the drill string; packer means inflatable into engagement with the bore hole to form an annular seal between said bore hole and the housing; and bore closure means for closing off the bore of the housing, said bore closure means including a bore closure member movably mounted in the bore of the housing, a piston mounted for movement in a cylinder in the housing, said piston being operatively connected to said bore closure means and being movable between a first position in which the bore of the housing is open and a second position in which the bore closure means closes off the bore of the housing, means for communicating said cylinder on one side of the piston with the bore of the housing, said cylinder on the other side of the piston defining a chamber which contains a compressible fluid, and first valve means normally isolating said communicating means and operable by a signal to open said communicating means to expose said piston to said fluid pressure in the bore of the housing to cause the piston to move to its second position to close off the bore of the housing.
2.
A device as claimed in claim 1 wherein said chamber contains gas at atmospheric pressure.
3.
A device as claimed in claim 1 wherein said communicating means is situated in said housing above the bore closure member.
4.
A device as claimed in claim 1 wherein said first valve means operable by a signal comprises a solenoid valve which is associated with means for receiving signals, which signal receiving means is operable to actuate said solenoid valve.
5.
A device as claimed in claim 1 and further comprising means to allow inflation of the packer means, comprising a one-way valve between the bore of the housing and the packer means, which one-way valve allows inflation of the packer means but prevents deflation of the packer means