| 摘要 |
A braking mechanism for avoiding a too sudden release of twist energy stored 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 chamber 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, namely from the first chamber, through the liquid pathway, and back to the second chamber. Reverse rotation of the pinion gears produces no pumping action.
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