File:Applied thermodynamics for engineers (1913) (14766387705).jpg

Identifier: appliedthermodyn01enni (find matches)
Title: Applied thermodynamics for engineers
Year: 1913 (1910s)
Authors: Ennis, William Duane, 1877-
Subjects: Thermodynamics
Publisher: New York, Van Nostrand
Contributing Library: The Library of Congress
Digitizing Sponsor: The Library of Congress

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LOCOMOTIVE 353 is ird-Lp ^ ttD til is work to be trans-mitted to the point ofcontact between wheeland rail without loss,and that the diameterof the wheel is D feet,then the tractive power,the force exerted atthe rim of the wheel,d-^LpD The value of p, withsuch valve gears as areemployed on locomo-tives, may be taken at80 to 85 per cent of theboiler pressure. Theactual tractive power,and the pull on thedrawbar, are reducedby the friction of themechanism; the latterfrom 5 to 15 per cent.Under ordinary con-ditions of rail, thewheels will slip whenthe tractive power ex-ceeds 0.22 to 0.25 thetotal weight carried bythe driving wheels.This fraction of thetotal weight is calledthe adhesion, and it isuseless to make thetractive power greater.In locomotives of cer-tain types, a tractionincreaser is sometimesused. This is a devicefor shifting some of theweight of the machinefrom trailer wheels todriving wheels. Theweight on the driversand the adhesion arethereby increased. Theengineman, upon ap-
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354 APPLIED THERMODYNAMICS proaching a heavy grade, may utilize a higher boiler pressure or a later cut-offthan would otherwise be useful. 510. Compounding. Mallet compounded the two cylinders as early as 1876.The steam pipe between the cylinders wound through the smoke box, thus becom-ing a reheating receiver. Mallet also proposed the use of a pair of tandem compoundcylinders on each side. The Baldwin type of compound has two cylinders on eachside, the high pressure being above the low pressure. Webb has used two ordinary ■outside cylinders as high-pressure elements, with a very large low-pressure cylinderplaced under the boiler between tlie wheels. In the Cole compound, two outsidelow-pressure cylinders receive steam from two high-pressure inside cylinders. Theformer are connected to crank pins, as in ordinary practice: the latter drive aforward driving axle, involving the use of a crank axle. The four crank effortsdiffer in phase by 90°. This causes a very regular rotative impul

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