The Circle of Knowledge

SOME GREAT MECHANICAL INVENTIONS

Steam Engines

What are steam engines?

Steam engines are machines in which the elastic force of steam is used as a motive power. In the ordinary engines the alternate expansion and condensation of steam imparts to a piston an alternating rectilinear motion, which is changed into a circular motion by means of various mechanical arrangements.

The engine is unquestionably the grandest and most influential for good of all the great inventions in the realm of physics. No other contrivance of man can be compared with this gigantic, yet tractable motor, in relieving both man and beast of ceaseless toil and irksome drudgery; in preventing suffering and starvation, and promoting intercourse, progress and civilization among the nations of the earth.

Give a description of the steam engine.

Every steam engine consists essentially of two distinct parts: the apparatus in which the steam is produced, and the engine proper. We shall first describe the former.

Steam Boiler.—The boiler is the apparatus in which steam is generated. Usually a cylindrical boiler is used for fixed engines; those of locomotives and of steam vessels are very different.

The steam is produced from water at a pressure considerably above that of the atmosphere, and is delivered to the engine with as little loss of pressure and heat as possible. The higher the pressure of the steam, the greater will be the amount of heat available, in a given weight of steam, for conversion into mechanical energy. Only a fraction of the total heat energy given to the steam in the boiler is converted into the mechanical work in the engine. By far the greater portion still remains in the steam after it has passed through the engine. The proportion of heat utilized depends on the thermal efficiency of the engine, amounting from twelve to fifteen per cent in good condensing engines; in the very best engines of large size it may be as high as twenty per cent.

The terms axis, axle, arbor, and shaft, in mechanics, are generally understood to mean the bar, or rod, which passes through the center of a wheel. A gudgeon is the pin, or support, on which a horizontal shaft turns; the pins upon which an upright shaft turns are called pivots.

The engine proper consists of a hollow cylinder closed at both ends; inside it is the piston, a sliding partition which fits the bore of the cylinder sufficiently close to prevent the steam leaking past it, but having sufficient freedom to allow it to move from end to end of the cylinder with as little friction as possible.

In modern engines the pressure of the atmosphere is not employed to drive the piston down. The steam is admitted into the cylinder above the piston at the same time that it is condensed or withdrawn from below, and thus exerts its expansive force in the returning as well as in the ascending stroke. This results in a great increase of power.

The practical construction of the piston and cylinder, and the arrangement of connecting pipes by which steam is admitted alternately above and below the piston, is fully shown in Figure A. This gives a sectional view of the cylinder, of the piston, and of the distribution of steam. The entire engine is of iron. To the piston, T, is fixed a rod, A, which slides with gentle friction in a tubulure, U, placed at the center of the plate which closes the cylinder. As it is very important that no steam shall escape between the piston-rod and this tubulure, the latter is formed of two pieces, one attached to the plate, while the other, which fits in the first, can be pressed as tightly as is desired, so as to compress the material soaked with fat which is between the two tubulures. This arrangement is called a stuffing-box; it prevents the escape of steam without interfering with the motion of the piston.

FIGURE A

Valve-Chest.—This is the arrangement by which steam passes alternately above and below the piston.

Figure A presents a vertical section of this valve-chest and shows its relation to the cylinder. The steam enters the valve-chest from the boiler by the brass tube x. From the valve-chest two conduits, a and b, are connected with the cylinder, one above and the other below. If they were both open at once, the steam, acting equally on the two faces of the piston, would keep it at rest. But one of these is always closed by a slide-valve, y, fixed to a rod, i. This moves alternately up and down, by means of an eccentric, e, placed on the horizontal shaft. The [899] slide-valve closes the conduit a, and allowing the steam to enter at b, below the piston, the latter rises. But when it reaches the top of the stroke the rod i sinks, and with it the slide-valve, which then closes the conduit b, and allows the steam to enter at a. The piston then sinks, and so forth at each displacement of the slide-valve.

It now remains to explain what happens when the steam presses below the piston. It must not remain above, otherwise the piston could not move. But while the steam enters below by the conduit b, the top of the cylinder, by means of the conduit a, is connected with a cavity, O, from which passes the tube L. Through this tube the steam which has already acted upon the piston passes into the atmosphere, or else is condensed in a vessel filled with cold water, which is called the condenser. If, on the other hand, the piston sinks, the vapor below the piston passes, by the conduit b, to the cavity O, and to the tube L.

Transmission of Motion.—The alternating rectilinear motion thus generated within the cylinder is transmitted, by means of a rod attached to the piston, to a strong beam ff, movable upon a central axis, a system of jointed rods ee, called the parallel motion, being interposed for the purpose of neutralizing the disturbing action which the circular path of the beam would otherwise exert upon the piston. The reciprocating motion of the beam is now, through the intervention of the connecting-rod g and crank h, converted into a circular or rotatory motion, which is rendered continuous and uniform by the fly-wheel i, to the axis of which the machinery to be impelled is connected.

The air-pump, p, for withdrawing the vapor and water from the condenser, the feed-pump, s, for supplying the boilers, and cold-water pump, t, for supplying the condenser cistern, are all worked by rods from the beam; and the governor, u, for maintaining uniformity of motion, is driven by a band from the crankshaft. The above description refers more immediately to that class of steam engines called low-pressure engines.

Types of Engines.—The various forms of the steam engine have received a varied form of classification. There are the general divisions into condensing and non-condensing engines, compound and non-compound, and single, double, or direct acting. Again there is the classification connected with the position of the cylinder, as in the horizontal, vertical, and inclined cylinder engines. Another classification divides steam engines into the uses to which they are applied, such as stationary engines, portable engines, marine, locomotive, electric generating, pumping, mill driving, winding, etc.

Steam Turbine.—The steam turbine, though the most modern form of the steam engine in practice, is the most ancient in actual history, the germ of the invention dating from Hero of Alexandria, in the second century B. C.

FIG. B—BEAM CONDENSING STEAM ENGINE

a, The steam-cylinder; b, the piston; c, the upper steam-port or passage; d, the lower steam-port; ee, the parallel motion; ff, the beam; g, the connecting-rod; h, the crank; ii, the fly-wheel; kk, the eccentric and its rod for working the steam-valve; l, the steam-valve and valve-casing; m, the throttle-valve; n, the condenser; o, the injection-cock; p, the air-pump; q, the hot-well; r, the shifting-valve for creating a vacuum in the condenser previous to starting the engine; s, the feed-pump for supplying the boilers; t, the cold-water pump for supplying condenser cistern; u, the governor.

One kind of steam turbine is really worked on the same principle as a windmill, only steam is used instead of the wind. Instead, however, of the sails making one revolution in seven or eight seconds, it sometimes makes three thousand revolutions a minute, or fifty revolutions a second. In another kind the blades of the turbine are something like the pockets on a water-wheel, and the steam shoves the wheel round by its great velocity.

Turbine engines are now fitted to vessels of large dimensions, up to ocean liners and battleships, with extremely satisfactory results. Turbine engines have also been applied in various other ways, e.g., to the driving of fans and blowers.

The principle of internal combustion, as used in gas and oil engines, has also been applied to the turbine with marked success, and has done much to solve the all-important problem of efficiency. It is extremely improbable that the long-range activities of the submarine would be nearly so effective were it not for the application of the same principle to their engines.

THE MARVELOUS IRON SKELETON OF THE LOCOMOTIVE AND THE NAMES OF ITS PRINCIPAL PARTS

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4	Air Signal Hose	77	Engine Truck Frame	150	Driving Box
5	Air Brake Hose	80	Engine Truck Equalizer	151	Driving Axle
11	Front Frame	82	Engine Truck Spring	155	Main Frame
12	Cinder Chute	86	Truck Brake	158	Go Ahead Eccentric
14	Extension Front	87	Wheel Guard	159	Back Up Eccentric
15	Headlight Step	88	Signal Pipe	165	Rocking Grates
16	Signal Lamp	92	Main Rod	168	Running Board
18	Smoke Arch Door	97	Main Frame	169	Air Cylinder Brake Pump
19	Smoke Arch Front	99	Air Drum	170	Steam Cylinder Brake Pump
22	Headlight Case	100	Pump Connection	173	Drip Cock
23	Headlight Reflector	101	Train Pipe Connection	174	Pump Piston Packing
27	Deflector Plate	102	Valve Stem Rod	177	Governor
28	Deflector Plate Adjuster	103	Train Pipe	186	Fire Box
29	Air Pump Exhaust Pipe	104	Wash Out Plugs	192	Stand Pipe
38	Smoke Stack	108	Link Block	195	Throttle Valve
39	Arch Hand Rail	112	Tumbling Shaft Arm	198	Dome
44	Steam Chest	113	Tumbling Shaft	201	Safety Valves
51	Steam Passages to Chest	114	Tumbling Shaft Lever	202	Chime Whistles
52	Valve Seat	120	Check Valve Case	203	Whistle Rig
56	Steam Ports	121	Check Valve	204	Ventilator
57	Cylinder	122	Flues	205	Cab
58	Back Cylinder Head	123	Oil Pipe	207	Air Gauge
59	Piston Packing	124	Horizontal Boiler Seam	208	Steam Gauge
60	Piston Rod	125	Circumferential Seam	209	Steam Turret
61	Piston Head	126	Boiler Lagging	213	Signal Whistle
62	Piston Packing Rings	127	Boiler Jacket	214	Air Pump Throttle
64	Front Cylinder Head	128	Jacket Bands	215	Throttle Lever
65	Cylinder Head Casing	132	Bell	216	Pneumatic Sander
66	Cylinder Lagging	133	Steam Bell Ringer	216a	Sand Lever
67	Cylinder Casing	134	Sand Box	217	Reverse Lever
68	Cylinder Cocks	135	Pneumatic Sander	218	Engineer’s Brake Valve
69	Cylinder Cocks Rigging	136	Sand Pipe	219	Gauge Cocks
70	Engine Truck	137	Driving Wheel Tire	222	Fire Door
71	Engine Truck Wheel	138	Driving Wheel Centers	229	Whistle Signal Valve
73	Engine Truck Axle	140	Driver Brakes	233	Signal Pipe
75	Engine Truck Box	141	Driver Springs	236	Feed Pipe