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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1916 Excerpt: ...may be longer than the other, as in a bob-tailed draw. Such cases will have to be given special consideration when they arise. In operating the end and centre wedges, the forces to overcome are the horizontal components of the vertical reactions on the wedges and the friction on each contact surface. This friction shall be taken at fifteen (15) per cent for each surface. In case toggles are used to lift the ends of the span, the friction in the toggle-joints shall also be taken at fifteen (15) per cent of the total load thereon. For operating the locks a proper allowance of power is to be made. The wedges and locks should be opened or closed in from fifteen (15) to thirty (30) seconds. 88. Lift Spans For vertical lift spans the friction on the journal shall be taken as twelve (12) per cent at the start and reduced by unity for each increase in speed of one (1) foot per minute at periphery of journal until the friction has been reduced to six (6) per cent. This force shall be reduced to an equivalent force at the rim of the tower sheave. If r = the radius of the journal, R = the radius of the supporting sheave, W = total moving load, the force in the operating ropes to overcome starting friction becomes 0.12 Wr Fl = R' The force at any other instant shall be determined in the same way by using the proper friction factor. The force necessary to overcome inertia is 32.2' where W = total moving load, and a = the linear acceleration. For spans opening in from one (1) to one and one-half (1H) minutes, the acceleration should take place in from ten (10) to twenty (20) seconds and the retardation in from ten (10) to fifteen (15) seconds. Where the time allowed for opening and closing is greater, the period of acceleration and retardation should be increased corresp...

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