| 摘要 |
A pump jack for traveling up and down a pole includes a frame member which supports a lower shackle having a front and a rear gripping rods applying a clamping force for gripping the pole. A pump arm pivotally supports and operates an upper shackle also having a front and a rear gripping rod for clamping the pole. The lower shackle has a single U-shaped yoke pivotally supported on and biased to a support arm to improve the leverage for operating the lower shackle. The upper shackle is provided with a freely rotatable roller mounted on the upper shackle so as to space the bitting front rod of the upper shackle from the pole to permit stepping up of the upper shackle. The usual tension springs on the upper shackle are eliminated to thereby permit less force needed for its operation.
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