| 摘要 |
A double-acting hydraulic unit (1) for telescopic booms comprises a cylinder (2) and a hollow piston rod (4) with a piston (3) that divides the cylinder into a piston side chamber (5) and a piston rod chamber (7). Two main conduits (10, 11) lead to the cylinder and two main conduits (10', 11') lead away from the piston rod to a co-operating hydraulic unit. Within the piston rod (4), there is a displaceable transmission element (16) that is arranged to actuate a locking device which in an active state engages into a seat (19) in a gable portion (8) to the cylinder (2). When the transmission element (16) is in an inner end position, the locking device (17) is inactive, whereby the piston (3) is freely movable relative to the cylinder. When the piston (3) reaches an outer end position at the same time as the actuation of the transmission element (16) by a carrier of an adjacent hydraulic unit terminates, then the transmission element is displaced axially, a wedge body (21) actuating the locking device (17) so that it engages into the seat (19). In this way the piston rod is locked mechanically and automatically in its outer end position.
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