| 摘要 |
An arrangement in a boom for a rock drilling unit, comprising a boom (1), pivotally connected to a frame (2) about a shaft (3), a lift cylinder (4) between the boom (1) and the frame (2), at the other end of the boom a feed beam pivotally connected about a shaft, parallel to the shaft (3), and a swing cylinder (10) between the feed beam and the boom. In the arrangement the lift cylinder (4) comprises three cylinder spaces, of which the first and second cylinder space (13a, 13b) may be connected to a hydraulic fluid supply for lifting or lowering the boom. The third cylinder space (13c) is inside a hollow piston rod (4b) and the cylinder comprises a fixed servo piston (4c) extending inside the piston rod. The third cylinder space (13c) is connected to the swing cylinder (10), to its first cylinder space (18a) and the second cylinder space (18b) of the swing cylinder (10) is connectable to a hydraulic fluid supply or receiver simultaneously with the first cylinder space (13a) of the lift cylinder.
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