CHAPTER I. GENERAL DESCRIPTION. Q. What are the essential features of a locomotive engine? A. (1) Boiler, (2) engines, (3)'running-gear. Q. What name is applied to the type of boiler usually employed for 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 non-compound, 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 engines 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? 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 * See special section under heading 66 Boilers," page 40. 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 noncompound 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 pay expenses, enough water to cool the exhaust. The time may * See special section on Compound Engines," page 499. come when by greater efficiency of the engine itself, calling for less steam per horse-power; by decreased friction of engine and of train, calling for less horse-power; and by increased efficiency of condensers themselves, calling for less water per horse-power—a locomotive may be run condensing; but that time is not yet. Q. What is a slide-valve? * A. A flat distributing-valve which has a to-and-fro motion upon a flat seat, usually in a direction parallel to that of the engine piston; this valve having in its working face one or more cavities, usually serving as a passage for the exhaust. Q. Do all locomotives employ slide-valves? A. Nearly every one that has been built has employed a slide-valve of one sort or another. Attempts have been made to use other types, but in general have been failures, not having the simplicity, durability, and range of work of the ordinary slide. Q. What is a link-motion engine?† A. One in which the valve (generally a slide) is moved by being connected with a bar or link (usually slotted) which receives a vibrating motion by connection with a rod attached to strap surrounding an eccentric disk set on a drivingaxle. There are usually two such disks for each cylinder, to enable reversing. The link position being varied, the amount of motion that it imparts to the valve may be altered at will. Q. Are all locomotives of the link-motion type? A. Most of them; but there is a system in which the valve is moved by an attachment to levers receiving their motion from the cross-head, or from the connecting-rod between the cross-head and the crank-pin; the amount of motion thus given being variable by slight changes in the relative and actual positions of the connecting-levers. * See special section on "Slide Valves," page 225. |