. American engineer and railroad journal . will take place at any speed. Thecalculations are simple, but care must be taken that theyare based on accurate data. To estimate the weights ofthe reciprocating parts from drawings is not sufficient ;they should be ascertained by actually weighing the fin-ished articles. engines with three cranks, althoughpartially balanced when at rest, are very far from balancedwhen at work, owing to the distance between the variousreciprocating parts, which consequently set up a rockingmotion, which is the principal one to be overcome, and insuch
. American engineer and railroad journal . will take place at any speed. Thecalculations are simple, but care must be taken that theyare based on accurate data. To estimate the weights ofthe reciprocating parts from drawings is not sufficient ;they should be ascertained by actually weighing the fin-ished articles. engines with three cranks, althoughpartially balanced when at rest, are very far from balancedwhen at work, owing to the distance between the variousreciprocating parts, which consequently set up a rockingmotion, which is the principal one to be overcome, and insuch engines this rocking motion we have to deal with inaddition to the vertical motion of the center of gravity,this vertical motion being due to the difference in weightof the working parts of the three engines. The positionsof the bob weights should be chosen so as to minimizetheir weight. What weight may be necessary to avoidvertical vibration of the center of gravity is constant, butwhat may be required to avoid rocking motiorr is dimin-. MODEL ILLUSTKATIN ished by an increased distance apart of the weights. Indouble-cylinder engines with the cranks at right angles itis a more pronounced galloping motion—that is, a motionof a kind, being a compound of vertical motionsof their center of gravity and a rocking motion. In a sin-gle-cylinder engine the vibration of the engine is prac-tically up and down ; but with whatever type of motion wehave to deal the same principle of balancing holds forces causing vertical vibration can be neutralized bythe use of bob weights, arranged to set up equal forcesacting in an opposite direction. Some years ago wethought the vibration in triple-expansion engines was dueto the difference in weight of the pistons, and with a viewto balance them and, as we supposed, avoid vibration, wemade each piston of the same weight in a first-class tor-pedo boat ; thus we prevented any vertical movements ofthe center of gravity of t
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectrailroadengineering
