| 摘要 |
An upstanding telescopic cylinder including piston and cylinder sections is provided and the piston and cylinder sections include large, inner and outer relatively telescopingly engaged guide sleeves with the cylinder guide sleeve disposed outermost. The piston section includes small and large diameter guide discs slidably mounted thereon with the small diameter disc lowermost and the piston sleeve includes longitudinally spaced sets of circumferentially spaced notched abutments which successively engage and elevate the large and small diameter discs during extension of the piston section. In addition, the piston section comprises a downwardly opening tubular member and the cylinder section includes a supply and return tubular member loosely telescoped into the tubular member defining the piston section and structure is provided for withdrawing downwardly through the supply and return tubular member, upon full retraction of the piston section, substantially all of the air which may accumulate in the cylinder section.
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