Engineers' Handy-Book; Containing Facts, Formulae, Tables and Questions on Power, Its Generation, Transmission, and Measurement, Together with a Discu
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. 1907 edition. Excerpt: ...termed a long and short leg, it is evident that the valve has an earlier and a freer exhaust at one end than at the other; nevertheless, one exhaust may be heavier than the other, and yet the intervals between them may be equal. In such cases the exhaust is equal as to time, but not as to amount. The difference in amount may be caused by unequal degrees of expansion, and this in turn may be caused by unequal cut-off, or unequal clearance, or both. Such inequality cannot be cured by mere adjustment, since the lap requires to be changed; but in most cases an imorovemeut may be effected by a compromise between equalized cut-off and exhaust, so that the effects of the inequality'of both would not be noticeable. In the case of fast-running engines, or where the exhaust has to pass through long pipes, this inequality is not easily determined from the appearance of the exhaust; but it may be done more accurately by holding the ear close to the exhaust pipe. This latter method may also be resorted to in the case of low-pressure engines exhausting into a condenser. How to Determine the Amount of Lap and Lead on a Valve without Opening the Steam-Chest, and whether it is Equal at both Ends or not. Open the cylinder drain-cocks and disconnect them from the drip-pipes, so that the steam may be seen and heard to issue from them. A better plan is, to open the holes made for the indicator, if there are any; at all events, open as large holes as possible; then let in a very little steam, turn the engine around by hand, and note, by the commencement and cessation of the flow of steam, j ust where the steam is admitted and cut-off. The point of cutoff can be most accurately ascertained by turning the engine backwards; the steam will in this case commence blowing at...
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