Blowout preventer with variable inside diameter

Claim 1

A blowout preventer adapted to seal with a pipe or other object in a well bore or to close same in the absence of any object in the well bore, comprising: a resilient sealing member having an inner surface adapted to engage a pipe of the like in a well bore; a rigid retainer plate mounted with the sealing member and having an inner surface generally conforming with the inner surface of said sealing member; means for urging said sealing member radially inwardly relative to said inner surface of said plate for effecting a seal with a pipe or the like in a well bore or with itself for closing a well bore; and first anti-extrusion means mounted with said plate and movable radially relative thereto in response to radial inward movement of said sealing member for preventing extrusion of the sealing member longitudinally in the area radially inwardly of said plate when fluid pressure acts on said sealing member, said anti-extrusion means including: a first set of anti-extrusion members spaced from each other and mounted for radial movement relative to said plate; a second set of anti-extrusion members, each mounted alternatively with respect to two anti-extrusion members in said first set; and interlocking means on said adjacent members for locking said adjacent members for radial movement together while premitting circumferential relative movement therebetween.