| 摘要 |
A hydraulic, walking, roof-support frame comprising a vertically-movable, pivotable control lever pivotally connected at its lower end portion to a rigid inextensible rocker arm pivotally mounted on a floor runner or skid of the frame and guided at a distance therefrom by a second rocker arm disposed nearer the coal-face end of the frame and pivotally connected to the floor runner and to the control lever, the free or coal-face end of the control lever being pivotally connected to a roof bar or plate pivotably born by hydraulic vertically-adjustable props, in which the said second rocker arm is longitudinally adjustable and is so constructed that it can be held at a predetermined intermediate length between pivots at its ends to enable its length to be changed in either direction as a result of a thrust from the roof.
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