LOCOMOTIVE CATECHISM CHAPTER I GENERAL DESCRIPTION Q. What are the essential features of a steam-driven locomotive engine? A. (1) Boiler, (2) engines, (3) running-gear. Q. What name is applied to the type of boiler usually employed for such locomotives?* A. Horizontal tubular with internal fire-box. Q. What name might be applied to the engines usually employed on locomotives? A. Twin horizontal double-acting high-pressure noncompound, non-condensing link-motion slide-valve engines. Q. Are all locomotive engines of the twin type? A. Nearly all; some, however (compounds, for instance), have the cylinder on one side of different diameter from that on the other; some have one cylinder on each side and one in the center; some again have four cylinders. Q. Are all locomotive cylinders horizontal? A. Nearly all; but some are slightly inclined downward toward the crank-pin, and while nearly horizontal are not strictly so. Q. What is the meaning of "double-acting"? A. An engine is double-acting when steam is admitted on both sides of its piston, instead of on only one, as in a Westinghouse stationary engine. Q. Are all locomotive engines double-acting? A. Yes. * See special section under heading "Boilers," page 30. Q. What is the meaning of "high-pressure"? A. It is a misnomer. The term came in when non-condensing engines were first made, to represent the difference between an engine which worked with high-pressure steam (either with or without a condenser, but particularly without) and one which worked usually by the aid of the vacuum produced by a condenser. Q. What is the difference between a compound and a non-compound engine? * A. In a compound the steam exhausted from one cylinder is passed into another, there to do more work as it expands further. In a non-compound the steam after being exhausted from one cylinder does not go into any other. Q. Is there any relation between compound and condensing engines; that is, may an engine be both? A. Yes; many engines, particularly marine, are both compound and condensing; that is, the steam after being exhausted from one cylinder, in which it has done work, passes into another cylinder, there to do further work, and then goes into a condenser. Q. What is a condensing engine? A. One in which the steam, after having done work in a cylinder, is exhausted therefrom at a certain pressure above vacuum or above the atmosphere, and at a certain temperature, then passes into a chamber where it is cooled by contact with a jet or spray of cold water, or with sheets or tubes cooled by cold water circulating on the other side thereof. Q. Are most locomotives non-compound? A. Yes; but compounds have been used in Europe for some years; and in this country, since 1890, orders for them have been increasing in proportion. Q. Are all locomotives non-condensing? A. Yes; it would be impossible, at least in the present state of steam engineering, to carry on a train that would * See special section on "Compound Engines." |