PART VI.

GENERAL DESCRIPTION OF A LOCOMOTIVE ENGINE.

QUESTION 63. _What are the principal parts of an ordinary locomotive engine?_

_Answer._ A boiler for generating steam and a pair of high-pressure steam engines, which are all mounted on a suitable frame and wheels adapted for running on a track consisting of two iron or steel rails.

QUESTION 64. _How is the power of high-pressure engines applied to locomotives?_

_Answer._ By connecting the engines with the wheels so as to give the latter a rotary motion.

QUESTION 65. _When they revolve what will occur?_

_Answer._ Either they will slip on the track, or the locomotive will move either backward or forward, according to the direction the wheels are turning.

QUESTION 66. _What will determine whether the wheels will slip or the locomotive move?_

_Answer._ The friction or _adhesion_, as it is called, between the wheels and the track. If this adhesion is greater than the resistance opposed to the movement of the locomotive, the latter will overcome the resistance; but if the latter is greater than the friction, the wheels will slip.

QUESTION 67. _Upon what does the amount of friction or adhesion of the wheels depend?_

_Answer._ Chiefly on the weight which they bear, but to some extent upon the condition of the rails. Under ordinary circumstances, the adhesion of the wheels of a locomotive is in direct proportion to the weight they carry.

QUESTION 68. _Why are two cylinders employed on locomotives?_

_Answer._ Because if only one was used, it would be impossible or very difficult to start the engine, if it should stop on one of the dead points.

QUESTION 69. _How is this difficulty overcome by the use of two cylinders?_

_Answer._ By attaching the two cranks to the same shaft or axle, and placing them at right angles to each other, so that when the one is at a dead point the other is in the position where the steam can exert the maximum power on the crank.

QUESTION 70. _How are the cranks of an ordinary locomotive made?_

_Answer._ They are cast in one piece with the wheels that drive the locomotive, which are therefore called _driving-wheels_. In this country the centre portion of such wheels, or _wheel-centres_ as they are called, is always made of cast iron, with tires of wrought iron or steel around the outside, and is fastened to the axles of the locomotive. The shaft of a locomotive engine is called the _main driving-axle_, and the wheels attached to it the _main driving-wheels_.

QUESTION 71. _How are the cylinders and driving-wheels of a locomotive usually placed?_

_Answer._ The cylinders _A_, plates I, II and III, are placed at the front end of the locomotive, and the main driving-axle, _B_, far enough behind them to permit the connecting rods, _C_, to be attached to pins, _D_, in the cranks, called _crank-pins_. In this country these cranks are now universally placed on the outside of the wheels, and therefore the cylinders must be placed far enough apart (as shown in fig. 40 and Plate III) to permit the connecting-rods to be attached to the crank-pins. The cylinders are therefore placed outside the frames, _H_, _H_, Plate III, (the latter are inside of the wheels,) and are now nearly always horizontal, although in old engines they are often inclined. Plate I is a side view of an ordinary eight-wheeled American locomotive, Plate II a longitudinal section, Plate III a plan, and fig. 40, a transverse section through the cylinder and smoke-box.

[Illustration: _Fig. 40._

Scale ¹⁄₄ in. = 1 foot.]

QUESTION 72. _What are the smaller wheels, E E, called, and what are they for?_

_Answer._ They are called _truck-wheels_ and carry the weight of the cylinders and other parts of the front end of the locomotive, and serve to guide and steady the machine in a manner which will be more fully explained hereafter.

QUESTION 73. _Why are more than one pair of driving wheels necessary for locomotives?_

_Answer._ Because if all the weight which is needed to create the requisite adhesion of the wheels of locomotives to pull heavy loads was placed on one pair of wheels, it would be so excessive as to partly crush and injure the rails. It is therefore distributed, usually on two pairs, but sometimes on three or four or even more pairs.

QUESTION 74. _Where is the second pair of driving-wheels usually placed?_

_Answer._ These wheels, _F_--called the _back_ or _trailing driving-wheels_--are, in the ordinary type of locomotives used in this country, situated behind the main driving-wheels, far enough back to give the room necessary for the boiler, _G_, between the two axles, as shown in plates I, II and III.

QUESTION 75. _How are the axles, cylinders, etc., held in the right position in relation to each other?_

_Answer._ By longitudinal frames, _H_, _H_, _H_, _H_, which hold the axles in the proper position, and are bolted to the cylinders, and also fastened to the boiler at _I_, _I_, Plate I.

QUESTION 76. _How is a locomotive engine made to run either backward or forward?_

_Answer._ By having two eccentrics, _J_, _J_, Plate III (also shown in Plate II,) for each cylinder. One of these is fixed or _set_ on the shaft in such a position as to move the valve so that the engine will run in one direction; the other eccentric is set so that the engine will run the reverse way. The ends of the two eccentric rods are attached to what is called a _link_, _L_, (Plates II and III,) the object of which is to furnish the means of quickly engaging and disengaging either eccentric rod to or from the rocker, _K_. The link is operated by a system of levers, consisting of the lifting shaft, _M_, and arms, _N_, _N_, and the reverse lever, _O_, _O_, (Plate II). The principles and working of these will be more fully explained hereafter.

QUESTION 77. _What are the principal parts or “organs” of a locomotive boiler?_

_Answer._ 1. A fire-place, or, as it is called a _fire-box_, _G_, (Plate II,) which is surrounded with water.

2. A cylindrical part, _P P_, (Plates I and II,) attached to the fire-box at one end and to a chamber, _Q_, called the _smoke-box_, at the other.

3. The tubes or flues _a a′_, (Plate II and fig. 40,) which connect the fire-box with the smoke-box and pass through the cylindrical part of the boiler and are surrounded with water.

4. The smoke-stack or chimney _R R_.

QUESTION 78. _What is each of these parts or organs for and of what do they consist?_

_Answer._ The fire-box _G_ furnishes the room for burning the fuel, and consists of an inner and outer shell made of boiler plate, with the space between the two filled with water; a grate, _b b_, (Plate II,) formed of cast-iron bars, with spaces between them for admitting air for the combustion of the fuel, which is placed on the top of them; a door, _C_, called the _furnace-door_, for supplying the grate with fuel; a receptacle, _d d_, below the grate, to collect ashes, and therefore called the _ash-pan_, which is supplied with suitable dampers, _n′_, _n′_, for admitting or excluding the air from the fire.

The cylindrical part _P P_, or _waist_ of the boiler as it is sometimes called, contains the greater part of the water to be heated.

The flues or tubes, as they are generally called, of which a locomotive has from one to two hundred, are usually two inches in diameter, and about eleven feet long. They conduct the smoke and products of combustion from the fire-box to the smoke-box. These tubes are made of small diameter so as to sub-divide the smoke into many small streams and thus expose it to a large radiating surface through which the heat is conducted to the water.

The smoke-stack serves partly for removing into the open air the smoke which passes through the flues, and partly for producing a strong draft of air, which is indispensably necessary for the rapid combustion of the fuel, and also for collecting and extinguishing the sparks from the fire.

QUESTION 79. _How is the draft produced in locomotive boilers?_

_Answer._ By conducting the exhaust steam through pipes (_e_, _e_, fig. 40) from the cylinders to the smoke-box and allowing it to escape up the smoke-stack from apertures, _f_, _f_, (Plate II, fig. 40.) called _exhaust nozzles_. The strong current of steam thus produced in the smoke-stack produces a vacuum, by which the smoke is sucked into the smoke-box with great power and forced out of the smoke-stack into the open air.

QUESTION 80. _How are the water and fuel carried which must be supplied to a locomotive while it is running?_

_Answer._ The water is carried in a tank, which is constructed in the form of the letter ~U~, so as to give room for the stowage of fuel between its two branches or sides. This tank is carried on a set of wheels, and forms a separate vehicle, independent of the locomotive, called a _tender_, the construction of which will be explained in a future chapter.

QUESTION 81. _What are the dimensions of the principal parts of a locomotive?_

_Answer._ There is a great variety in the plan, size and capacity of locomotives, but the type which is more generally used in this country than any other, and which has been selected for the preceding illustrations, and will be described in the succeeding chapters of the Catechism, has four driving and four truck wheels, and weighs in working condition about 60,000 lbs. The following are the dimensions of its principal parts: The driving-wheels are about 5 feet and the truck-wheels from 26 to 30 inches in diameter. The longitudinal distance between the centres of the driving-wheels is usually about 7 feet, and between the centres of the truck-wheels 5 ft. 9 in., and the total distance from the centre of the back driving-wheels to the centre of the front truck-wheels, which is called the _wheel-base_, is 21 ft. 8 in. The weight on each driving-wheel is usually about 10,000 lbs., and on each truck-wheel about 5,000 lbs. The cylinders are 16 in. in diameter and the piston has 24 in. stroke, and the connecting-rod is 7 ft. long measured between the centres of the pins to which it is attached. The centres of the cylinders are about 6 feet apart, measured across the track. The fire-box inside is 5 feet long and 2 ft. 11 in. wide, and the cylindrical part of the boiler is 4 feet in diameter measured on the outside of the smallest portion. The water spaces around the fire-box are about 3 inches wide. There are 140 tubes, which are 2 in. in diameter measured on their outside, and 11 ft. long. The inside of the smoke-stack is 16 in. in diameter, and it is 14 ft. 3 in. high measured from the top of the rails. The tender carries about 1,800 gallons of water and about 8,000 lbs. of coal. When loaded it weighs about 40,000 lbs., making the total weight of the engine and tender 100,000 lbs.

The following is a list of parts designated by the letters of reference on plates I, II, III and fig. 40.

_A_, _A_, Cylinders. _B_, Main driving-axle. _C C_, Main connecting-rods. _D D_, Main crank-pins. _E_, _E_, Truck-wheels. _F_, Axle of trailing-wheels. _G_, Fire-box. _H_, _H_, _H_, Frames. _I_, _I_, Frame-clamps. _J_, _J_, Eccentrics. _K_, _K_, Rockers. _L L_, Links. _M_, Lifting-shaft. _N_, _N_, Lifting arms. _O O_, Reverse-lever. _P P_, Cylinder part of boiler. _Q_, Smoke-box. _R R_, Smoke stack or chimney. _S_, Pilot or cow-catcher. _T_, Head-light. _U_, Bell. _V_, Sand-box. _W_, Whistle. _X_, Dome. _Y Y_, Cab or house. _Z_, Back or trailing-wheel crank-pin. _A′_, Pump air-chamber. _B′_, _B′_, Main driving-wheels. _C′ C′ C′_, Supply-pipe. _D′_, Front platform. _E′_, Bumper timber. _F′ F′_, Back driving-wheels. _G′_, Coupling-pin. _H′_, Friction-plate. _I′_, Check-valve. _K′ K′_, Foot-board. _L′_, Lazy cock. _M′_, Mud drum. _N′ N′_, Driving springs. _P′_, Pump. _R′_, Drop-door or grate. _S′_, Steam gauge. _T′ T′_, Feed pipe. _U′ U′_, Forward eccentric rods. _V′ V′_, Backward eccentric rods. _X′_, Lifting-shaft spring. _Y′ Y′_, Dampers. _Z′_, Pushing-bar. _a a′_, Tubes. _b b_, Grate. _c_, Fire-box door. _d d_, Ash pan. _f f_, Exhaust-nozzles or blast-pipes. _g_, Safety-valve lever. _h h_, Cross-heads. _i i_, Running-board. _j_, Throttle-stem. _l_, Throttle-pipe. _m m_, Dry pipe. _n_, T-pipe. _o o_, Steam-pipe. _p_, Petticoat pipe. _q_, Smoke-box door. _r_, Piston. _s_, Spark-deflector or cone. _t t_, Wire-netting in stack. _u u u_, Boiler-lagging. _v v_, Truck-spring. _w w_, Sector or quadrant. _x_, Blow-off cock. _e k_, Reversing-rod. _y_, Truck centre-pin. _z_, Throttle-lever. _a′ a_, Tubes. _b′ b′_, Truck frame. _c′ c′_, Bed-plate. _d′_, Boiler brace. _e′ e′_, Sand pipe. _f′ f′_, Equalizing lever for driving wheels. _g′ g′_, Guide-bars or rods. _h′ h′_, Receptacle for sparks. _i′ i′_, Bell rope. _j′ j′_, Guide yoke. _k′_, Valve-stem. _l′ l′_, Truck equalizing lever. _m′ m′ m′_, Hand-rail. _n′_, Blow-off cock in mud drum. _o′_, Spring balance. _p′_, Pump plunger. _q′ q′_, Foot steps. _r′_, Brace to smoke-box and frame. _s′ s′_, Steam-chests. _t′ t′ t′_, Crown-bars. _u′_, Head-light lamp. _v′_, Main valve. _w′_, Blow-off cock handle. _x′_, Bell-crank for throttle-valve. _y′_, Piston-rod. _z′_, Draw-bar.