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