... in the oil field workover operations on dumping 23/8" ,-3½"drill pipe, and 2 7/8"- 4½" tubing and 4 ... surface of clamping rollers climbing, cards tight, reliable and timely release. 3, the first with the upper and lower clamp Fuzheng outside ... , matching clamp back, reversing valve can be manually manipulated simultaneous release clamping or string. 5, friction braking institutions in the clamp ...