| 摘要 |
A pumping unit has a drive train comprising a very large mass including large diameter series connected sheaves, one of which is a large crank sheave. The crank sheave is directly connected to a pitman arm which oscillates a walking beam, which in turn reciprocates a horsehead attached to a bridle. The bridle is connected to a polished rod associated with a downhole pump. The crank wheel, pitman arm, and rocking beam are arranged respective to one another to cause the tail bearing to oscillate predominantly in the second quadrant, and to cause the center of gravity of the pitman arm to be located predominantly between the vertical axis of the crank wheel and the Samson post bearing. The geometry of the crank wheel, pitman arm, and rocking beam provides substantially constant, positional of the polish rod on the downstroke, with rapid positional occurring at peak polish rod velocity, which causes a longer downhole pump stroke because of the induced elongation of the sucker rod string.
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