| 摘要 |
A self-advancing mine roof support has at least two extensible hydraulic props, mounted on blocks of elastomeric material, and a prop aligning or positioning means. The latter comprises a retractable and extendable device operative between the props of the support so as to be responsive to angular movement thereof and operative or operable to give the props an initial setting attitude when the support has been relieved of the roof load. A preferred form of retractable and extendable device is a hydraulic ram having a pressure fluid cylinder attached to one prop and a piston working in said cylinder and acting substantially vertically on a foot or member projecting laterally from the other prop. A single prop aligning or positioning means may be arranged to align or position three, four or more props of a support.
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