| 摘要 |
An internal bypass free piston provides for continuous flow of gas during upward and downward travel of the piston; the piston is structured to rotate during downward travel to equalize wear and the frictional force between wall and piston is utilized to maintain the position of parts of the piston during upward as well as downward travel and is readily adjusted; further, such frictional force is automatically maintained at a higher value during upward motion than in downward motion in the well tubing.
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