Hydraulically operated heavy lift system for vertically moving a string of pipe

Apparatus for longitudinally moving at substantially constant velocity a string of pipe having collars at fixed intervals along the pipe string, said apparatus comprising:

• first and second releasable collar engaging means, first and second reciprocating linear drive means spaced along the pipe string for stroking the collar engaging means reciprocally lengthwise of the pipe string between a pipe collar engaging position and a pipe collar releasing position, control means for each of the linear drive means and associated collar engaging means, said control means including means for cycling the first and second drive means through successive drive cycles, the drive means during each drive cycle moving the associated collar engaging means during half of each cycle at a first control operating velocity through a distance equal to half the distance between the two collars, and moving the associated collar engaging means at slightly slower velocity in the same direction at one end of the limit of travel for a small portion of the second half cycle, at a slightly higher velocity in the same direction at the other end of the limit of travel for a small portion of the second half cycle, and in the reverse direction during the remainder of the second half cycle, the drive cycles of the first and second drive means being a half cycle out of phase.