DIFFERENT KINDS OF LOCOMOTIVES.
QUESTION 427. _Into what classes may locomotives be divided
conveniently?_
_Answer._ 1. Locomotives for “switching,” “shunting” or “drilling”
service, that is, for transferring cars from one place to another at
stations; 2, for freight traffic; 3, for ordinary passenger traffic,
and 4, for suburban or metropolitan railroads, where a great many light
trains are run.
QUESTION 428. _What kinds of locomotives are used in this country for
switching cars at stations?_
[Illustration: Fig. 220.]
_Answer._ Four-wheeled locomotives similar to that shown in Plate IV.
In some cases they are made with six driving-wheels. Engines like that
shown in Plate IV have separate tenders, but they are sometimes made so
as to carry the water-tank and fuel on the locomotive itself, as shown
in fig. 220, and are then called tank locomotives. Fig. 220 represents
a switching engine built by the Taunton Locomotive Manufacturing
Company.
QUESTION 429. _Why are four-wheeled locomotives used for switching?_
_Answer._ Because in such service it is constantly necessary to start
trains, many of which are very heavy, and therefore a great deal of
adhesion is needed. For this reason the whole weight of the locomotive
and in the case of tank locomotives that of the water and fuel is
placed on the driving-wheels. It is also necessary for such locomotives
to run over curves of very short radius and into switches whose angle
with the main track is very great, and therefore in order that they may
do this and remain on the track, their wheel-bases must be very short,
and consequently the wheels are all placed near together between the
smoke-box and fire-box.
QUESTION 430. _Why are such locomotives not suited for general traffic?_
_Answer._ Owing to the shortness of their wheel-bases they become
very unsteady at high speeds, and acquire a pitching motion, similar
to that of a horse-car when running rapidly over a rough track. This
unsteadiness not only becomes very uncomfortable to the men who run the
locomotive, but there is danger of the engine running off the track.
As nearly all switching is done at very slow speeds, it is not so
objectionable for that service as it would be on the “open road”[102]
at high speeds.
[102] The term “_open road_” is a literal translation from the
German, for which there is no corresponding English term, and means
the road between stations where trains run fast.
QUESTION 431. _What kinds of locomotives are used for freight service?_
_Answer._ The greater part of the freight service of this country is
performed by locomotives like that selected for the illustrations
of these articles, and represented in Plates I, II and III. Such
locomotives have been called “American” locomotives because they first
originated in this country and are now more generally used here than
anywhere else. Side elevations of locomotives of this kind, built by
the Baldwin Locomotive Works, the Grant Locomotive Works, the Danforth
Locomotive and Machine Company, the Mason Machine Works and the Hinkley
Locomotive Works are represented in Plates V, VI, VII, VIII and IX.
Such locomotives have been described in the preceding pages.
QUESTION 432. _What are the dimensions of such engines?_
_Answer._ The principal dimensions of the engines illustrated are given
in the table in the appendix, but locomotives of this plan are built
of much smaller and also of larger sizes than those represented by the
engravings. In some cases such locomotives do not weigh more than 35 or
36,000 lbs., with cylinders from 8 to 12 inches in diameter. In other
cases they weigh as much as 66,000 lbs., with cylinders 17 or 18 inches
in diameter. The wheels vary from 4 to 6 feet in diameter, but the most
common sizes are 4¹⁄₂ and 5 feet.
QUESTION 433. _When it is desirable to pull heavier loads than
is possible with the adhesive weight that can be placed on four
driving-wheels, what is done?_
_Answer._ One or more pairs of driving-wheels are added, as in
the ten-wheeled locomotive represented in Plate X, the “Mogul”
engine, Plate XI, and the “Consolidation” engine, Plate XII. The
ten-wheeled locomotive, it will be seen, is similar in construction
to an ordinary American locomotive, excepting that it has another
pair of driving-wheels in front of the main driving-wheels. It will
be seen, however, that it is necessary to keep these close to the
latter, because if they are brought further forward they will be too
near the back truck-wheels. For this reason a truck consisting of a
single pair of wheels, _A_, _A_, is placed in front of the cylinders,
as represented in Plates XI and XII, is now much used. The front
driving-wheels are then placed further forward, and thus bear a larger
proportion of weight than they do in locomotives like that shown in
Plate X.
QUESTION 434. _How are trucks with a single pair of wheels constructed?_
_Answer._ The truck frame is extended some distance behind the
truck-axle, as shown in fig. 221, and the centre-pin, _a_, about which
it vibrates, is placed at the back end. The weight of the locomotive,
or that portion to be carried on the truck, is then made to rest over
the centre of the axle, but in such a way that it can move laterally
or crosswise over the track. Such trucks were first made so that the
weight of the engine rested on slides on the truck frame, but recently
they are nearly always suspended on links, so that they can swing like
a pendulum, as shown in figs. 190 and 191. The weight of the engine
then rests on the centre-plate, _H H_; which forms part of the plate,
_B B_. This is suspended by links, _L L_, represented by dotted lines,
which are attached by bolts to the cross-pieces, _m m_, which are
fastened to the truck frame. In this way the truck-wheels can move
sideways independent of the engine itself. As the wheels and axles, _A
A_, must move about the centre-pin, _a_, fig. 221, the axle assumes a
radial position to the curves of the track. It does this, too, quite
independent of the driving-wheels, as is shown in fig. 221, which
represents a plan of the wheels on a curve. It will be seen that the
truck is not at all influenced by the position of the driving-wheels.
This arrangement therefore gives great flexibility to the wheel-base,
and enables the wheels to adjust themselves to any lateral curvature or
alignment of the track.
[Illustration: Fig. 221. Scale ¹⁄₈ in. = 1 foot.]
QUESTION 435. _For what purpose are locomotives like that shown in
Plates XI and XII used?_
_Answer._ “Mogul” locomotives are often used for ordinary freight
service where heavy trains must be hauled, and also on steep grades.
“Consolidation” locomotives, represented in Plate XII, which have eight
driving-wheels, are employed almost exclusively for traffic over heavy
mountain grades.
QUESTION 436. _What other kinds of locomotives are used for freight
traffic?_
_Answer._ Various kinds of tank locomotives, that is, locomotives which
have no separate tenders, but carry the water-tanks and fuel on the
frame and wheels of the locomotive itself, have been devised and are to
some extent used. Plate XIII represents a locomotive of this kind on
which the tanks are placed on each side of the boiler, and the fuel on
a Bissell truck at the back end. A similar truck is placed at the front
end, so that a locomotive of this kind can run equally well either way.
The lateral movement of the two trucks also gives great flexibility to
the wheel-base, so that such an engine will adjust itself easily to
the curvature of the track. If, however, the two pairs of truck-wheels
should both stand on an elevated part of the track, and the
driving-wheels on a depression, the latter would evidently not carry as
much and the truck-wheels would carry more of the weight of the engine
than they did on a level part of the track. If the reverse condition
of things should occur, that is, if the driving-wheels should be on an
elevation and one or both pairs of the truck-wheels on a depression,
then the latter would bear less weight than they did and the
driving-wheels more. For this reason, in order to distribute the weight
evenly on all the wheels, it is necessary to equalize the weight on the
truck and driving-wheels, by connecting them with equalizing levers,
similar to those which were described in answer to Question 301. These
levers distribute any undue weight which may come on one wheel to that
next to it. This is important, because if the driving-wheels bore less
weight at some times than at others, their adhesion and their capacity
to draw loads would be reduced in like proportion.
It is evident, however, that if the water-tank or fuel is carried on
the driving-wheels, there will be a greater weight on them when the
tank is full than when it is empty, and that therefore there will
either be so much weight on the wheels at one time as to be injurious
to the rails, or else there will be too little for adhesion at another.
Of course cases are conceivable, and doubtless exist in practice, where
more adhesion is required to start a train and haul it during the
first part of the “run” than will be needed during the latter part. In
such cases doubtless the variable character of the weight might be an
advantage instead of the reverse, but for ordinary practice a variable
load on the driving-wheels would have the disadvantages which have been
described. For this reason tank locomotives have been built like that
represented in Plate XIV. In this it will be seen that the weight of
the water-tank rests on a four-wheeled truck at the back end. A Bissell
or two-wheeled truck is, however, placed in front in the same position
as in the engine represented in Plate XIII, and carries a portion of
the weight of the boiler and machinery.
In order to get all the advantages which a four-wheeled switching
engine possesses in having its _whole_ weight on the driving-wheels,
and at the same time avoid the disadvantages which result from a
short wheel-base, and also from a varying amount of weight on the
driving-wheels, a locomotive like that represented in Plate XV was
designed by the writer with the whole weight of the boiler and
machinery resting on the driving-wheels, and the water and fuel on a
truck. By this means not only the objections to carrying the weight
of the water on the driving-wheels is overcome, but at the same time
the disadvantages arising from the short wheel-base of the switching
locomotive, Plate IV, are also obviated. That is, all the _permanent
weight_ of the boiler and machinery of such a locomotive rests on the
driving-wheels, and is therefore all _adhesive weight_, as it is in the
switching engine, and at the same time by extending the frame beyond
the fire-box and placing the water-tank and fuel on this extension
of the frame and supporting their weight on a truck, the engine has
a wheel-base which is as long and as flexible as that of ordinary
American engines, represented in Plates V, VI, VII, VIII and IX, and
as the latter have only about _two-thirds_ of their weight on the
driving-wheels, locomotives like that represented in Plate XV, of the
same weight as the others, have fifty per cent. more adhesion, or they
may be one-third lighter and have the same adhesion. As was explained
in answer to Question 260, if an ordinary American locomotive runs
backwards, that is, with the driving-wheels in front, the friction of
their flanges against the rails on curves of short radius will be very
excessive. To avoid this with locomotives of the design last described,
they are run with the truck first, which, being at the opposite end
of the boiler from the position which it usually occupies, reverses
the position of the boiler and other parts relative to the motion of
the engine. That is, the fire-box is then in front and the smoke-stack
behind. Engines of this kind have been built and are now working and
doing excellent service; but the prejudice which exists against running
locomotives in the reverse direction to what has been customary seems
to be the chief obstacle in the way of their use.
Another plan which possesses all the advantages of the locomotive
described above and is free from the last objection is represented
in Plate XVI. This plan was first adopted by Mr. Robert Fairlie in
England, but has been introduced into this country and very much
improved by Mr. William Mason, of Taunton, Mass. In these locomotives,
the driving-wheels and cylinders are attached to a truck frame which
turns around a centre-pin like any ordinary truck. The steam and
exhaust pipes are connected to the boiler and cylinder with pipes which
have flexible joints. By this means the truck can move independently
of the boiler, and thus the driving-wheels can adjust themselves to
the curvature of the track, just as the wheels of any other truck do,
and therefore the driving-wheels can be run ahead just as well as the
truck-wheels which carry the tank. This plan possesses the additional
advantage that the fire-box can be made as wide and as long as may
be desired without interfering with the driving-wheels. The flexible
pipes are, however, usually considered an objection; but with the
improvements which have been made in their design and construction,
the difficulties which were at first encountered have probably been
overcome. At any rate if there is no other objection to the use of such
locomotives, ingenuity and care should in time overcome that one. Plate
XVII represents a locomotive of this plan, with six driving-wheels
and a six-wheeled carrying truck under the tank. This latter plan of
locomotive is intended for heavy freight traffic.
QUESTION 437. _What kind of locomotives is used for passenger trains?_
_Answer._ Eight-wheeled American locomotives are used almost
exclusively for passenger service. Usually the driving-wheels of
such locomotives are larger in diameter than are used for freight
traffic. Their size varies from 5 feet to 5 ft. 9 in. in diameter. The
locomotive by the Mason Machine Works represented in Plate VIII has
5¹⁄₂ feet driving-wheels. For very heavy express trains locomotives
with 17 × 24 inch cylinders and weighing 34 tons are now used on many
through lines.
QUESTION 438. _What is meant by suburban and metropolitan railroads,
what is the nature of their traffic, and what kinds of locomotives are
needed for it?_
_Answer._ The traffic of suburban railroads consists chiefly of the
transportation of passengers who do business in the city to the latter
in the morning and to their homes in the evening. As the largest
number of passengers must be carried during a few hours in the morning
and evening, it is necessary to run very heavy trains at those times.
As the passengers must be distributed at many stations which are near
together, it is necessary to stop often; and in order that the average
speed may be reasonably fast the trains must run very rapidly between
these stations. It is therefore necessary to have heavy locomotives,
with more than the usual proportion of adhesive weight, so that the
trains can be started quickly without slipping the wheels. The main
valves should also have a liberal amount of travel, so that steam will
be admitted to and exhausted from the cylinders quickly. In some cases
it is thought desirable to have locomotives which will run equally well
either way, so that it will not be necessary to turn them around at
each end of the “run.”
By metropolitan railroads are meant railroads in large cities. They
may be divided into two classes, one for carrying freight cars from
the outskirts of cities to the warehouses and stores at their business
centres, and also from the terminus of one road to that of another.
Metropolitan railroads of this kind are usually branches of lines
which extend from the city. Locomotives for such traffic must have
great tractive power, in order to pull heavy trains, and as the speed
is usually slow the wheels and the boiler capacity may be small.
They must generally be capable of running through curves of very
short radius; and as the traffic is usually carried through streets
in close proximity to buildings, the locomotives should be as nearly
as possible noiseless. The other class of metropolitan roads is for
carrying passengers. The traffic of the latter is similar to that
usually carried on horse railroads, and consists almost exclusively of
passengers. At present (1874) there are only one or two metropolitan
railroads in this country for carrying passengers which are operated by
steam power. It seems certain, however, that their use will soon become
very general in all large cities. Their traffic will consist of many
light trains run at short intervals and at comparatively slow speeds,
and therefore very light locomotives are required.
QUESTION 439. _What kinds of locomotives are used for suburban
railroads?_
_Answer._ The ordinary American eight-wheeled locomotive is used
more than any other kind; but a number of locomotives like that
represented by fig. 222 have been built and are used for this traffic.
These have one pair of driving-wheels in front of the main pair and
a Bissell truck in front of the cylinder. With this arrangement the
driving-wheels bear a larger proportion of weight than they do if
arranged on the ordinary American plan with a four-wheeled truck.
Another plan is that shown in Plate XVIII. Such engines, as will be
seen, have a Bissell truck at each end, and therefore they run equally
well either way. In some cases the tanks of such engines are carried on
the top and sides of the boiler. When they are obliged to run only a
short distance, and a small supply of water is needed, this arrangement
answers very well; but it is impossible to carry a large supply of
water in this way without overloading the wheels of the locomotive,
and at the same time increasing the evils of a varying load on the
driving-wheels.
[Illustration: Fig. 222.
LIGHT PASSENGER AND FREIGHT LOCOMOTIVE, BY THE GRANT LOCOMOTIVE WORKS,
PATERSON, N. J.]
Locomotives like that shown in Plate XIV are also used for suburban
traffic. As shown in the engraving they have a four-wheeled truck at
one end and one with two wheels at the other, so that it is thought
that they can be run safely either way. The four-wheeled truck carries
the weight of the water and fuel.
The plan of engine represented by Plate XV is very well adapted for
this kind of traffic. Excepting on curves with a very short radius
it could be run in either direction at any required speed, without
encountering any other difficulty excepting the prejudices of those who
run it.
As double-truck locomotives similar to that shown in Plate XVI can
adjust themselves to any curve, this objection could not be urged
against their use.
QUESTION 440. _What kinds of locomotives are used on metropolitan
railroads?_
_Answer._ For freight traffic ordinary switching locomotives like that
represented in Plate IV are often employed. In some cases these have
the tanks on the locomotives. It often happens, though, that such
traffic must be conducted in the streets of a city, and that the noise,
especially of the exhausting steam, is thus liable to frighten horses
and disturb the occupants. It is, then, necessary either to condense
the exhaust steam or render its escape noiseless, which is done by
allowing it to escape into the water-tanks. Street locomotives which
have a condenser similar to the surface condensers used on marine
engines are used on the Hudson River Railroad in New York. The exhaust
steam passes through these and then escapes into the tanks. The latter
are long and narrow, so as to expose a great deal of surface to
radiation, and in this way cool the water which becomes heated by the
steam. The engines have four driving-wheels and vertical boilers. The
cylinders are connected to a crank shaft with a pinion on it, which
gears with another wheel of larger size on the driving-axle. In this
way the speed is reduced and great tractive power can be exerted. The
whole of the engine is enclosed so as to hide the machinery, the sight
of which is supposed to frighten horses. The engines were designed and
patented by Mr. A. F. Smith, formerly Master Mechanic of that road.
For roads in cities carrying passengers almost exclusively, an entirely
different class of locomotives is needed. To suit passengers it is of
course necessary to run a great many trains at very short intervals.
When this is done the trains are necessarily very light, and therefore
only light locomotives are needed. Plate XIX represents the locomotives
employed on the Greenwich Street Elevated Railroad in New York. These
engines weigh only 10,000 lbs., and the wheels are 30 in. diameter
and the cylinders 7 × 10 in. The peculiarity in their construction
consists in their having an intermediate shaft between the two pairs
of driving-wheels. This shaft has two cranks inside of the frames and
two outside. The cylinders are connected to the inside cranks, and the
coupling-rods to those on the outside. The water is carried in a tank
on top of the boiler. The fuel is anthracite coal.