| 摘要 |
The double-acting hydraulic cylinders of the lift system are connected in a master-slave series relationship. When the cylinders have been retracted to a predetermined extent, a control valve between the last slave and a primary selector valve of the system is mechanically closed responsive to the arrival of the cylinders at such retracted condition and, simultaneously, the master is prevented from further retraction by either mechanical means or another hydraulic control valve between the master and the primary selector valve. Thus, the cylinders and their interconnecting lines are cut off from inadvertent overcharging, as well as fluid escape, so that all cylinders remain uniformly extended with drift from their established positions. Several circuit arrangements are disclosed, including provision for bleeding off higher than necessary operating pressures tending to become trapped within the cylinders and their associated flow lines after the cylinders have reached the intended point of retraction.
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