| 摘要 |
A multi-lift mast for a forklift has hydraulic circuitry that provides free lift and negative lift capabilities for the forklift. The mast comprises a stationary member, at least one extensible member slideable on the stationary member and a carriage slideable on an extensible member. The extensible mast members are raised and lowered by double acting hydraulic actuators extending between the stationary member and an extensible member. The carriage is raised and lowered by a positively connected double acting carriage hydraulic actuator extending between an extensible mast and the carriage. The circuitry employs identical pairs of counterbalance valves controlling the supply and exit of hydraulic fluid for the bore and rod ends of the actuators, set to cause the carriage to fully extend before the extensible mast members extend, providing free lift, and set to cause the extensible mast members to fully lower before the carriage lowers. The hydraulic circuitry prevents the extensible masts from rising when forks of an elevated carriage are inserted in receivers on a hauling vehicle and the circuitry is operated as if to lower the carriage, causing the carriage to pull up the extensible mast and so lift the forklift off the ground (negative lift) for piggybacking on the hauling vehicle.
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