| 摘要 |
A derrick having boom rotation brake release means operable to allow the boom to be rotated by side loading above a predetermined magnitude and thereby relieve the extent of side loading so as to avoid damage to the derrick. The boom is rotated by a hydraulic motor with which is associated a double relief valve that allows reverse operation of the motor as an idler pump while imposing a limited resistance to rotation. The brake release means is hydraulically operated to release a brake mechanism that normally prevents boom rotation, with the brake release means being connected in the hydraulic system of the derrick for operation to release the brake mechanism in response to an increase in the hydraulic pressure in the system occurring during operation of the rotation motor and also during operation of other hydraulically operated derrick functions to allow the boom to rotate during operation of the rotation motor and to be rotated by side loading during operation of the other derrick functions, with the resistance of the rotation motor preventing rotation until a predetermined magnitude of side loading is imposed. Deactuation of the rotation motor and all of the other derrick functions results in a pressure decrease that renders the brake release means inoperable to allow the brake mechanism to prevent further rotation of the boom when the derrick functions have been completed or at any time that it becomes necessary to stop boom rotation, e.g., to avoid damaging contact with an adjacent object.
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