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US Patent: 26,871
Enos G. Allen - Boston, MA

USPTO Classifications:
73/715, 92/94

Tool Categories:
propulsion and energy : steam apparatus : stationary boilers : steam pressure gauges

Henry O. Allen - Malden, MA

American Steam Gauge Co. - Boston, MA
National Steam Gauge Co. - Boston, MA

Albert W. Brown
Robert L. Harris

Patent Dates:
Granted: Jan. 17, 1860

Patent Pictures:
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"Vintage Machinery" entry for Enos G. Allen
"Vintage Machinery" entry for American Steam Gauge Co.
Last in a trio of interesting steam-gauge patents by Enos G. Allen. "In the construction of steam gages, the spacing or graduating of the dial plate constitutes a very expensive part of the manufacture, as each dial has to be marked differently from the others. This difficulty arises from the fact, that it has been found impossible to manufacture any number of the springs which communicate the pressure of the steam to the index hand exactly alike, and so that they shall all possess the same amount of tensile power. The nearest approach to accuracy has heretofore been attained by the use of a volute spring tapering both in width and thickness as described in the schedule of Letters Patent of the United States, granted to me (patent 26,152). But I have found in practice, that it is impossible to so make these springs that they shall be all exactly alike, owing partly to their form, they being too thin to permit their being planed down from the bar of steel of which they are made, to the required shape or so as to taper two ways and consequently are constructed entirely by forging, which is not only an expensive operation but one which precludes the possibility of obtaining perfect accuracy in the spring, as the steel so forged cannot be uniform throughout... The present invention consists in constructing the volute spring of a bar of steel of uniform thickness throughout and tapering in wide on one side only, which form of spring I have found by repeated tests to produce the most accurate results, as the bar of steel, which when coiled, constitutes the spring, can as it is of uniform thickness, be reduced the to the required shape by planing, thereby avoiding the imperfections and great expense of forging. Moreover this form of spring enables me, without difficulty or great cost, to manufacture all the springs so exactly alike that instead of being obliged to mark each dial plate by accurate and actual experiments, so as to correspond with its spring, as has heretofore been necessary, I am enabled to prepare the dial plate by electrotyping, as any spring will answer for any dial..."

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