| 摘要 |
A braking mechanism for avoiding a too sudden release of twist energy stor ed in a rod string on shut down or power failure, includes a gear pump which incorporates two meshing pinion gears that define a first and a second chamb er within the gear pump cavity. A liquid pathway leads from the first chamber to the second chamber and contains flow-restricting means such as a nozzle or valve. The pinion gears are mounted such that pumping takes place only in one direction, namel y from the first chamber, through the liquid pathway, and back to the second chambe r. Reverse rotation of the pinion gears produces no pumping action due to a relatively large space between the pinion gear teeth and the wall of the cavity, and th e relatively close mesh of the two pinion gears with each other. One of the pinion gears is mounted on a shaft which is geared to a portion that rotates with the rod string.
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