GB1174809A - Improvements in or relating to a Hydraulic Lifting Apparatus - Google Patents

Abstract

1,174,809. Platform elevators. YAWATA IRON & STEEL CO. Ltd., and TOKYO KEIKI SIEZOSHO CO. Ltd. 14 May, 1967 [16 March, 1966], No. 11862/67. Heading B8H. [Also in Division F1] An hydraulic load lifting apparatus has a plurality of lifting cylinders 6-9 movable in synchronism by hydraulic fluid supplied by a main pump 1, the output of which is divided into separate streams by passage through a plurality of coupled motors M, one for each cylinder, the thus possibly slightly differing flow rates to each cylinder being automatically adjusted to the same rate by valves 10-13, each controlling the supply to a particular cylinder of additional fluid from an auxiliary pump 14. A solenoid operated changeover valve 15 allows the valves 10-13 to adjust the flow rate from the cylinder during lowering of the load. If any cylinder reaches its lowermost position ahead of the other cylinders, the creation of a vacuum therein is prevented by the opening of an associated non-return valve 17, 18, 19 or 20 to admit hydraulic fluid from a reservoir. In the event of any cylinder reaching its uppermost position ahead of the other cylinders the excess pressure is released through an associated non-return valve 21, 22, 23 or 24 and a relief valve 25. A low-pressure relief valve 32 may be connected so as to replace the relief valve 25 by operation of a solenoid valve 26, whereby fluid may be flushed from the apparatus without raising the load. Each cylinder has an individual solenoid valve 27, 28, 29 or 30 independently operable to supply hydraulic fluid from a further pump 31 or exhaust fluid for independent adjustment of the lifting cylinders. Differences in the extensions of the units are corrected by appropriate operation of the solenoid valves in response to displacement error signals emitted by synchronous motors.