After passing over the head block , the lines are fastened by chains and turnbuckles to a counterweight carriage . The turnbuckles enable the set to be trimmed . The carriage runs up and down , usually at the wall , travelling a distance equal to that travelled by the flown pipe . The weights are pig-iron , added incrementally until the set is counterbalanced to a degree that permits manual operation by pulling on a manila purchase line to the top of the carriage , running over...











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