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A differential pulley, also called "Weston differential pulley", sometimes "chain hoist" or colloquially "chain fall", is used to manually lift very heavy objects like car engines. It is operated by pulling upon the slack section of a continuous chain that wraps around pulleys. The relative size of two connected pulleys determines the maximum weight that can be lifted by hand. The load will remain in place (and not lower under the force of gravity) until the chain is pulled.〔Macauley, David with Ardley, Neil. The New Way Things Work. p.56. Houghton Mifflin Company, Boston, USA 1998. ISBN 0-395-93847-3.〕 ==History== The differential pulley was invented in 1854 by Thomas Aldridge Weston from King's Norton, England.〔Hoist Magazine - (The history makers )〕 The pulleys were manufactured in collaboration with Richard and George Tangye. According to Richard Tangye's autobiography, the Weston differential pulley evolved from the Chinese windlass, with an endless chain replacing the finite length of rope. He claimed that many engineering firms conceded on the difficulty of efficiently disengaging the chain from the teeth as the pulleys turned, but his firm developed a "pitch" chain which solved the issue. Marketed as "Weston Differential Pulley Blocks with Patent Chain Guides", the pulley had good sales, namely, 3000 sets in 9 months. It was displayed in 5 sizes — from to — at the 1862 International Exhibition in London and received a medal for "original application, practical utility and success". An ironmonger challenged the Tangyes that the pulley had been in use for 30 years before Weston's patent but the judge, William Page Wood ruled in favour of the Tangyes because the engaging mechanism was substantially different from the one presented as evidence.〔Powerhouse Museum, Sydney, Australia - (2003/45/1 Differential pulley block, large and small sheaves, 2 ton (2.032 tonnes) capacity, invented by T A Weston / made by Tangyes Ltd, Birmingham, England, 1860 - 1890 )〕 The Yale Lock Company acquired the patent rights in 1876.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Differential pulley」の詳細全文を読む スポンサード リンク
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