Back-up power tongs

Back-up power tongs for holding a tubular member against rotation of a connected tubular member, comprising:

• a. a body, having a center opening of sufficient size for a tubular member to pass therethrough, a slot communicating between the edge of said body and said center opening, said slot having a width greater than the diameter of said tubular member, and a cavity disposed within said body;
• b. a plurality of jaw members disposed within said body around the perimeter of said center opening, each said jaw member having a concave surface generally conforming to the curvature of said tubular member and facing the interior of said center opening so as to be grippingly engageable with said tubular menber;
• c. at least one cylinder assembly, disposed within said cavity and fixedly connected to one said jaw member so as to extend or retract said jaw member on a radial path centered at the center of said tubular member, said cylinder assembly including:
• i. a cylinder body, fixedly connected to said jaw member at one end and having a cylinder cavity opening from the interior of said cylinder body to the other end of said cylinder body;
• ii. a piston, having first and second ends, positionable within said cylinder cavity, and having a piston head at said first end slidingly and sealingly positionable within said cylinder cavity, and a piston rod extending between said piston head and said second end, said second end being fixedly positionable within said body cavity, and sealingly attachable to said other end of said cylinder body so as to slidingly seal said cylinder cavity from the exterior of said cylinder body, said piston further having a first fluid port communicating between said first and second ends, and a second fluid port communicating between said second end and the exterior of said piston rod behind said piston head, said first and second ports being connectable at said second end to a fluid system.