| 摘要 |
Oil supply line (13) connects an oil supply pump (11) and the hydraulic balancing line (9) with said supply line having an electric control valve (15). Position sensors (17, 18) are placed respectively on the auxiliary arm (4) and on the principal arm (3) neighboring the articulation of the beam (5) of the counter weight. If the auxiliary arm is detected in its pendulum position, while the beam of the counter weight is not yet detected in its vertical position, the electric valve is commanded by an automat (16) and extra oil is supplied to a jack (8) to place the beam in a vertical position.
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