同时分析了下冲程抽油杆所产生的螺旋弯曲变形。
Deformation of helical buckling appeared on rod during down stroke is also analyzed.
该项工艺省去原机械举升中的油管，利用空心杆作为传动介质和油流通道，下冲程挤压排液。
This technique eliminates the tube in conventional mechanical lifting, takes hollow rod as the transmission medium and oil flow channel and discharges fluid during down stroke.
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