Importance

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Abstract

A synchronous lifting or lowering system with hydraulic cylinders controlled by parallel-connected lift valves having two fluid passages. Hydraulic fluid for extending or retracting the actuators is delivered by a hydraulic supply system alternating between the two passages. Each time the supply circuit alternates passages, a fixed volume of hydraulic fluid is transferred during lifting or received during lowering by the respective lift or lowering valves to or from the cylinders causing the rods to lift or lower a proportionate amount. All of the rods extend during advancement or retract during lowering by approximately the same increment each time the supply circuit alternates passages. Because the rods all extend or retract the same increment each cycle, the load is lifted or lowered evenly and the need for height sensors or transducers is eliminated.

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First Claim