1. Field of the Invention
This invention relates to telescopic hydraulic hoist mechanisms, and in particular to such mechanisms that are made from rolled aluminum stock, are fast-acting; have greater bearing life and air breathers for the space between hydraulic stages, thereby preventing dirt from being sucked into the hydraulic mechanism.
2. Related Art
The Commercial Intertech Distribution Services Hydraulic Cylinder Division catalogue, (Date ?) pages 24-34 illustrates a number of "Dump Cylinder Identification Drawings" each representing a particular telescopic hydraulic mechanism respectively identified as: "ANTHONY"; "COMMERCIAL"; CUSTOM HOIST"; "FONTAINE"; "PEABODY GALION"; "GLENCO/FARMHAND"; "HEIL "OLD STYLE""HPT SERIES"; "HEIL "NEW STYLE" HPT SERIES"; "HYCO 900-2000 SERIES"; "HYCO 10,000 SERIES"; "HYCO 30,000 SERIES"; "HYCO 70,000 SERIES"; JOHNSON"; "LESSARD";"MAILHOT/"C" MODEL"; "MAILHOT/"M" MODEL COVER TUBE DESIGN"; "MARION MFCG."; NORDIC/NORD-SEN METAL INDUSTRIES"; "PERFECTION"; "PERFECTION FARM HOISTS"; "PRINCE"; and "WARD CO". These telescopic hydraulic dump cylinders collectively disclose various state-of-the-art features of such mechanisms, for example an oil port in the base trunnion and various seal mechanisms.
Additionally, U.S. Pat. No. 3,958,376 to Campbell and entitled: "Extendible Tower Structure" discloses a plurality of nesting tower sections that can be telescopically raised into an extended position for supporting a load thereat. Hydraulic cylinders within the tower sections extend the tower sections.
U.S. Pat. No, 4,928,488 to Hunger and entitled: "Hydraulically-Operated Support Device for Semitrailers" discloses an extending cylinder in the bottom of which is formed a load-raising cylinder for a load-raising piston. A pump subassembly includes three independently operable pumps for generating and controlling the hydraulic operating pressure.
Finally, U.S. Pat. No. 4,471,944 to Leray et al. and entitled: "Telescopic Jack" discloses a plurality of coaxial tubular telescopic elements mounted within a cylinder and each pair of adjacent tubular telescoping elements has two pairs of cooperating annular recesses on their inner and outer surfaces which cooperate with an elastic ring to limit the outward movement of an inner tubular element relative to its adjacent outer element.
The prior art telescopic hydraulic mechanisms are prone to abnormal wear of their bearings, operate slowly, have inadequate sealing which admits dirt into the hydraulic cylinders and are heavy.