File:A manual of marine engineering- comprising the design, construction, and working of marine machinery (1907) (14763413791).jpg

Identifier: marineen00seatmanualofrich (find matches)
Title: A manual of marine engineering: comprising the design, construction, and working of marine machinery
Year: 1907 (1900s)
Authors: Seaton, Albert Edward, 1848-1930
Subjects: Marine engineering
Publisher: London, C. Griffin and company, limited New York, D. Van Nostrand co.
Contributing Library: University of California Libraries
Digitizing Sponsor: MSN

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ne tend to tilt and twist on its bed. Moreover, sincethe momentum of the balance weight is constant tangentially, while that ofthe pistons, rods, &c., ceases at the ends of the stroke, there must be anexcess momentum of the balance weight at those periods which, in thevertical engine, tend to make it move horizontally, and in the horizontalengine vertically. This evil is made apparent in a locomotive engineby what is called rail hammering, from the blows the rail gets fromthe wheels with the balance weights when the engine passes the deadcentres. If the balance weight is placed on one crank-arm only, as was some-times done for cheapness, similar actions were set up, but less in degree.Two balance weights, one on each arm, make the proper balance, but stillfail to avoid the horizontal overbalance when the crank passes the deadpoints and the consequent horizontal vibration. If only balance weightsopposite the cranks can be provided, a compromise must be arrived at, so BALANCING. 537
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538 MANUAL OF MARINE ENGINEERING. that their weight is such that the horizontal vibration due to overbahmceis reduced to that of the vertical vibration caused by underbalance. If,however, the engine has an air pump, &c., worked by means of levers sothat they move in the opposite direction to that of the piston, their weightniay be so adjusted that their momentum balances that of the piston androds, while the balance weights on the crank balance the crank, pin brasses,and connecting-rod end. There will, however, still remain a couple tendingto rock the engine athwart ship. Mr. Macalpine has designed a quadruple engine (fig. 200) with thecylinders in pairs, one behind the other, and each pair operating on thesame crank by means of rocking levers like those of the air pump. Thisgives, no doubt, a very well balanced arrangement fairly free fromvibration, but the ratio of maximum to mean torque is greater than thatof a thi-ee-crank engine. Further, the motion of the valve and gear in t

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