_THE WESTINGHOUSE AIR-BRAKE._
INVENTION OF THE WESTINGHOUSE ATMOSPHERIC BRAKE.
In this exacting age, the traveling public are much more disposed
to find fault with systems that do not provide against fatalities
resulting from human fallibility, than to commend the perfection of
appliances which annually save more lives than would be lost in a
sanguinary war. The Westinghouse brake has performed this life-saving
service, yet its great conserving merit has been but feebly appreciated
outside of railroad circles. During the decade between 1860 and
1870, America became a reproach among nations for the frequency and
disastrous nature of its railroad accidents. To-day fewer railroad
travelers in America lose their lives by accidents beyond their own
control, than the travelers in any country under the sun. The credit
of this immunity from fatal accidents is almost entirely due to the
successful operation of the Westinghouse and other brakes that followed
the line suggested by this invention.
DISTINCT CLASSES OF INVENTIONS.
Inventions may be divided into two distinct classes. Far the more
numerous class are those which effect improvements on recognized
appliances. The other is the rare and more valuable class, to which
belongs the original inventor who devises an entirely new method for
performing a desired operation. Among this class of inventions may
be noted Watt’s separate condenser, which first rendered the steam
engine a commercial success; the multitubular boiler of Nathan Read,
which made a high-speed locomotive practicable; and the air-brake of
Westinghouse, which made fast traveling safe, by putting the train
speed under the control of the engineer.
BENEFITS CONFERRED ON TRAIN MEN BY GOOD BRAKES.
To the traveling public the air-brake has proved a source of
satisfaction by assuring exemption from accidents, but its greatest
blessing has been conferred upon train men. Being the greatest
sufferers from railway accidents, their risks of life and limb are
greatly reduced; and the agonizing helplessness that used to be so
often experienced with trains that could not be stopped in time to
avoid a disaster, is almost unknown on our well-managed roads. Mind has
become victor in its conflict with matter. When necessary, an engineer
can run a train at a high velocity over crowded lines without having to
shut off steam within a mile of each point where there may be another
train obstructing the track, or keep up his speed at the risk of his
life. People unacquainted with the inside operating of railroads have
no idea of the difficulties train men had to contend with in getting
fast trains over the road, before continuous brakes were supplied.
The train had to be run on schedule time, and all points where trains
might be expected had to be approached with care. This meant reduced
speed; and speed could not be reduced in short distances, so the risk
had to be taken of violating one rule to comply with another.
FIRST TRIALS OF THE WESTINGHOUSE ATMOSPHERIC BRAKE.
The Westinghouse atmospheric brake was patented April 13, 1869; and
the first public trial took place on the Panhandle road about the same
time. The trial was so satisfactory, that the Pennsylvania Railroad
Company, which have been always noted for their liberal patronage of
every meritorious device likely to promote the efficiency and safety
of railroad operating, had a train equipped with the brake. This was
the Walls accommodation train, a kind of service where frequent stops
were required, and was therefore well calculated to demonstrate the
true character of any brake. A number of public trials were made with
the brake thus fitted, among which was one by the Master Mechanics’
Association in the middle of September, 1869, on the Horseshoe Bend
on the Pennsylvania Railroad. Here a train of six cars, running down
a grade of 96 feet to the mile, at the rate of 30 miles an hour, was
stopped in a distance of 420 feet. Such a feat was unprecedented at
that time, and attracted wide-spread attention.
In the following month, official trials of the train were made by the
officers of the Pennsylvania Railroad near Philadelphia. The train was
then taken to Chicago, where numerous tests were made in the presence
of leading Western railroad officers. So convincing were these trials
of the decided efficiency of the brake, that, immediately afterwards,
the Michigan Central Railroad and the Chicago and North-Western
Railway each ordered a train to be fitted with the brake.
FIRST ROADS THAT ADOPTED THE WESTINGHOUSE BRAKE.
The first five sets of the Westinghouse brake fittings made were got
out in the shops belonging to the Pennsylvania Railroad Company at
Altoona, Penn. The first railroads to adopt the brake as a regular part
of their equipment, were the Pennsylvania, the Pittsburg, Cincinnati,
and St. Louis, the Union Pacific, the Chicago and North-Western, and
the Michigan Central Railroads.
Since the Westinghouse atmospheric brake was first tried, many changes
in details have been made, and numerous improvements have been
effected; but the essential points remain the same. And the best forms
of brakes subsequently got out by other inventors are founded on the
Westinghouse idea, just as much as the numerous types of locomotives
follow the design of Stephenson’s Rocket.
OUTLINES OF THE ATMOSPHERIC BRAKE.
Although the automatic air-brake is now becoming almost universal
in American railroad practice, most train men are familiar with the
working of the atmospheric brake under the name of “straight air.”
When first invented, the Westinghouse brake consisted of an apparatus
located on the locomotive for compressing air, which was stored in an
iron drum fastened somewhere about the engine. Underneath each car,
and connected with the ordinary brake attachments, was a cylinder
containing a piston, which operated the brake. The brake-cylinders
were kept in communication with the air-drum on the locomotive by iron
pipes. Connection between the cars where “stretching” and “compression”
made the train vary in length, was made by means of rubber flexible
hose. When the engineer wished to apply the brakes, he admitted the
compressed air into the supply pipes, through a three-way cock at his
hand. This air entered the cylinders under the cars, moving back the
pistons which pulled the levers operating the brakes. To release the
brakes, the air was permitted to escape out of the pipes into the
atmosphere.
Thus, what is really a complicated operation was performed in a simple
manner, and by means of machinery not liable to get out of order
readily. The instant application of every brake on a long train was
put in the hand of the engineer. On the first indication of danger,
his hand became powerful beyond the magical forces conceived by the
imagination of poets.
HOW EASTERN RAILROADS KEPT ALOOF FROM THE WESTINGHOUSE BRAKE.
The growth of the Westinghouse brake into public favor furnishes a
curious commentary on the different degrees of enterprise to be found
among railroad companies in the various sections of this country. It
was natural to suppose that railroads in the thickly settled States,
where trains had become too numerous for being safely operated with
crude brakes, and no signals, would have been the first to adopt an
improved appliance which gave promise of increased safety. Yet the
railroads in the Eastern States, with a few creditable exceptions,
were among the last to patronize the Westinghouse brake; and they
adopted it only when the influence of public opinion could no longer be
ignored. Western railroads that ran through sparsely settled prairies,
where trains were rare, and stopping room generally ample, were among
the first to encourage the inventor of the brake with their support.
LESSON OF THE REVERE RAILROAD ACCIDENT.
During the first two years after it was invented, the Westinghouse
brake made slow progress into practical application, except in the
West. In the ancient State of Massachusetts, it was hardly known till
the Revere accident happened near Boston. This was the case of a
crowded road being operated without signals or brakes, except those
of the most primitive description. A fast express train ran into the
rear end of an accommodation train, killing twenty-nine persons, and
severely injuring fifty-seven others. The engineer of the express
train, while running at a speed of twenty-five miles an hour, saw the
tail lights of the accommodation train when he was eight hundred feet
away. He whistled for brakes, and reversed his engine; but the train
could not be stopped.
The railroad superintendents throughout the conservative State of
Massachusetts then received enlightenment respecting the existence
of an efficient continuous brake in a vigorous fashion. The Revere
accident conveyed its lessons in a terrible way, but they were
effectual in convincing railroad managers that they could not afford to
dispense with a brake that proved itself to be reliable.
WEAK POINTS OF THE ATMOSPHERIC BRAKE.
Although the atmospheric brake could, with light trains, make stops
within the shortest distance it was desirable to stop trains with
safety to the passengers and rolling stock, it possessed certain weak
points which demanded remedy. In case of a train breaking in two,--an
accident which frequently happens, especially on rough track,--there
was danger of the engineer applying the brake without knowing that an
interval existed between the cars, and allowing the rear end of the
train to crash into the forward part. The signal given by the bell-rope
breaking, had a tendency to lead to an accident of this character.
Another objection to straight air was, that should derailment take
place, or any accident happen that would rupture the pipes or their
connections, the brake was rendered useless. These weak features did
not interfere with the working of ordinary traffic; and as providing
special appliances to meet cases of accident which are rare, does
not generally receive much consideration, the brake might have been
regarded as perfect enough for all practical purposes had it not failed
to meet satisfactorily a condition of ordinary train service. As the
length of trains was increased, it was found that the atmospheric brake
was slow in action. When a long array of pipes and many cylinders
had to be charged with air from the drum on the locomotive after the
necessity for applying the brake became apparent, and before it would
act, some seconds were required for the operation. Every additional car
put upon the train increased the length of pipes and the cylinders to
be filled, and so lengthened the time that elapsed between the instant
danger was perceived and the time at which the brake began to perform
its retarding work. The increase of time might be only a few seconds,
but they would probably be priceless moments when an accident was
impending.
THE WESTINGHOUSE AUTOMATIC AIR-BRAKE.
To overcome this line of weakness, the Westinghouse automatic air-brake
was invented. Where good station signals are in use, it has long been
accepted as an axiom among railway authorities, that a signal must be
constructed so that it will indicate danger when any accident happens
to its mechanism. This principle was brought into practical application
in the Westinghouse automatic air-brake. When any thing goes wrong with
the brake apparatus, its tendency is to apply the brake automatically.
A break in a pipe makes the brake fly on. Each car carries a supply
of compressed air sufficient to apply its own brakes several times.
By the new arrangement, the brakes on all the cars are applied almost
simultaneously, and instantly after the engineer turns the handle of
his stopping-valve. The brakes are applied by decreasing the pressure
in the pipes; so the breaking in two of the train, or the fracture of
an air-pipe or coupling, sets the brakes on all the cars on the train,
whatever side of the break the cars may be on. That in itself is an
invaluable feature in a continuous brake, and prevents cars from acting
as battering-rams upon each other in cases of derailment.
LIFE-SAVING VALUE OF THE AUTOMATIC BRAKE.
Every few days, notices get into the public prints relating how
frightful accidents were prevented by the prompt action of the
automatic air-brake. And hundreds of narrow escapes, where this brake
proves the preventive of destruction to life and property, receive no
record, and are known only to the employes connected with the operating
of trains. To the men familiar with train service, to those who are
intimately acquainted with the life-saving effected by the automatic
air-brake, it seems surprising that railroads could have been operated
without this or a similar appliance. They certainly were not operated
safely without it.
FIRST RAILROADS THAT ADOPTED THE WESTINGHOUSE AUTOMATIC AIR-BRAKE.
Patents for the Westinghouse automatic air-brake were granted in March,
1872. During the succeeding winter, trials of the brake were made by
the Pennsylvania Railroad; and it was shortly afterwards adopted by the
Philadelphia and Reading Railroad Company as their standard brake for
passenger trains. The example of that company was soon followed by the
St. Louis, Kansas City and Northern, the Chicago and Alton, the Toledo,
Wabash and Western, and the St. Louis, Iron Mountain and Southern
Railroads, all of which companies equipped their passenger rolling
stock with the automatic air-brake within a few months.
ESSENTIAL PARTS OF THE WESTINGHOUSE AUTOMATIC AIR-BRAKE.
The prominent features of the Westinghouse automatic air-brake consist
of the following leading parts: An air-pump, placed on the locomotive,
is operated by a steam cylinder, which forces air into an iron drum or
reservoir placed under the deck, or in any other convenient part about
the engine. The air is compressed to the density considered necessary
for the kind of train the locomotive usually pulls.
In the cab, located conveniently to the hand of the engineer, is the
engineer’s brake-valve, commonly called the “three-way cock,” which
regulates the flow of air from the main reservoir into the main
brake-pipes for supplying the auxiliary reservoirs with air. This
valve applies the train-brakes by letting the air escape from the main
brake-pipes, and releases them by again admitting the pressure of air
into the pipes.
From the main reservoir, the main brake-pipe connects with the
engineer’s valve, and thence along the train, supplying all the brakes
with the air required.
Under the floor of each car is fastened an auxiliary reservoir, which
holds a supply of air necessary for operating the brakes on that car.
So each car carries its own supply of air.
Connected with each car-truck is a brake-cylinder, in which is operated
a piston that applies the brake. The brake-levers connect with the
piston-rod in such a manner, that, when the piston is forced out by the
air-pressure, the brake is applied.
Attached to the auxiliary reservoir is the triple valve, whose action
connects the air-cylinder with the auxiliary reservoir.
THE AIR-PUMP.
When the air-brake was first invented, the distribution of steam
within the cylinder was effected differently from what it is in modern
pump-cylinders. The steam-valve consisted of a double piston, the
heads having ports on their edges which admitted and released the
steam. This valve did not move up and down, but received an oscillatory
motion from a small auxiliary engine placed on the top of the steam
cylinder-head. The movements of the auxiliary engine were regulated by
a reversing-rod (popularly known as a kicker-rod), working inside the
main piston-rod. This arrangement of steam distribution was somewhat
complicated, and liable to get out of order; and it was superseded by
the differential steam-valve movement now in use.
HOW THE AIR-PUMP WORKS.
[Illustration: FIG. 33_a_.]
In Fig. 33_a_, steam enters from the boiler at the nipple 35, and
fills the steam-space between the heads of the main piston-valve 15,
16, maintaining a constant pressure of steam there while the pump
is at work. The upper head of the main valve being of greater area
than the lower one, the tendency of the pressure is to raise the
valve. A downward movement of the valve is provided for by a separate
single-headed piston-valve 20, working in a cylinder above the main
valve. The reversing-rod 12 operates a slide-valve 13, which regulates
the admission and release of steam for the third piston.
In the cylinder shown in the engraving, the main valve is down, so that
steam is passing into the lower end of the main cylinder. Two small
ports can be seen close to the piston-head 16, one above the other. The
upper port is open, and is the admission port; the lower port, which
is closed by the small piston, is for exhausting the steam. The main
piston 7 is on its upward stroke, and the upper exhaust port seen
above the piston-valve 15 is open, while the steam port immediately
below it is closed by the valve-piston in the same way that the exhaust
port is closed at the other end. When the main piston 7 shall reach
near the top of its upward stroke, the plate 10 will strike on the
projection on the reversing-rod, pushing up the slide-valve 13. The
upper edge of this slide-valve will cut the steam off the passage
_a_, and open the passage _b_ to the exhaust. This takes the steam
away from the piston 20, and allows piston 15 to move upward, closing
the exhaust-port, and opening the upper steam-port. The same movement
makes the piston 16 close its steam-port, and open the exhaust. Piston
7 now begins to travel downward; and, when it reaches nearly to the
bottom of the cylinder, the plate 10 catches the knob on the end of the
reversing-rod, and pulls down the slide-valve 13 to the position it
holds in the engraving. Steam then rushes through the passage _a_, and
makes the piston 20 push down the main valve. That completes the circle
of the operations in the steam cylinder.
HOW THE AIR-END OPERATES.
[Illustration: FIG. 33_b_.]
The operation of the air part of the pump is very simple. While the
main piston (Fig. 33_b_), which is on the same rod as the piston of
the steam cylinder, is moving upward, it is forcing the air out of the
upper end of the cylinder up under the discharge-valve 32, and away
through the proper passages to the main reservoir. At the same time the
lower end of the cylinder is being filled with air drawn through the
lower receiving-valve 34. During the downward stroke of the piston, the
air will be delivered through the valve 33, and the upper part of the
cylinder filled by air received through the upper valve 34.
AIR-PUMP DISORDERS.
An engineer who does not understand the principles of a locomotive’s
action, is not likely to prove a valuable runner. The men who are most
successful in getting trains over the road with solar regularity; the
men who make the best records on the mileage sheets for economy in
fuel and in lubricants; who are lightest in repairs, yet keep their
engine going longest,--are those who comprehend the functions of every
portion of the engine, and what relation the various parts bear to
each other. With this knowledge clearly established in the mind of the
runner, his power to detect any thing wrong with his engine becomes
instinctive. Trifling defects, which neglect would develop into serious
disabilities, are rectified in time, and the whole engine is maintained
in smooth working-order by the harmony of its individual sections. The
mere stopper and starter is losing his hold on the locomotive service.
When he drops off entirely, our mileage for each dollar expended will
be decidedly increased.
The principles which apply to the running of a locomotive are equally
applicable to the management of an air-brake, with all its perfected
connections. This apparatus can not be properly managed unless the man
who works it knows something about its action.
PUNY DIFFICULTIES VANQUISH THE IGNORANT ENGINEER.
A great many engineers who run passenger trains, and take an
intelligent interest in the working of the locomotive, whose
technicalities they have thoroughly mastered, display no desire
whatever to understand the air-brake, and are perfectly contented
with its action so long as it will stop the train. The air-pump,
so wonderfully interesting to those who understand its movements,
receives no more attention than is necessary to keep it going so that
the required air-pressure is maintained. They know how to start and
stop the machine, and they oil it regularly; but these are the limits
of their attentions. Should the pump happen to stop working, the cause
is mysterious, like many other mysteries; and the natural remedy
suggested, is to hit the thing on the head with a monkey-wrench. Should
it not respond to this treatment by renewed action, the hand-brakes are
resorted to for the rest of the journey; and the round-house foreman or
machinist is required to do the head-work which locates the trouble.
A belief prevails among men who labor principally with their hands,
that laziness is exclusively physical. This is a mistake. It is a
psychological fact, well known to metaphysicians, that mental laziness
is prevalent enough to dwarf the minds of half the human race. Men who
would willingly work with their hands during half their leisure time to
keep their engines in proper condition for running, have to be driven,
by fear or jealousy, before they will force their mental faculties to
do trifling labor in a new channel.
CAUSES THAT MAKE BRAKES INOPERATIVE OFTEN EASILY REMEDIED.
Any engineer of ordinary intelligence, who will spend one hour a day
for two weeks studying up the Westinghouse instruction book, will
understand the brake so well, from the pump to the hind end of the
train, that any imperfection happening to its working will be as
readily located as an ordinary defect in a locomotive. Yet it is an
intensely hard matter to induce men running passenger engines to go
through this trifling mental exercise. The consequence is, that the
brake sometimes becomes inoperative from causes so slight that men
should be ashamed to report them; and they would be so if they only
comprehended how small a mole-heap became their mountain. I knew a case
where all the train men--that is to say, engineer, fireman, conductor,
baggageman, and brakemen--wrestled for twenty minutes over a triple
valve, trying to find out how to cut the air off a car; and, when the
crowd was vanquished, a colored porter came, and showed them how the
thing was done. This was on a road where straight air was generally
used. One day some winters ago, a passenger train on the road I worked
for was delayed an hour or more at a station, waiting for something.
When the engineer tried to start the air-pump, it would not work.
He fumed and fussed over it for fifteen minutes, gave it a liberal
dose of copper hammer medicine, and saturated it with oil, but all to
no purpose. It would not pump a pound of air, so the old-fashioned
Armstrong was called into operation. In the course of its journey, this
train had to pass the round-house at headquarters; and the engineer
stopped to see if his pump could be given some quick remedy. I happened
to be the doctor consulted. On learning the particulars of how the pump
stopped working, I set fire to a piece of greasy waste, and held the
flame to the check-valve of the air-drum; and the pump went right to
work. All the trouble was, that the check-valve was frozen in its seat.
I felt sorry for that engineer, he appeared to be so thoroughly ashamed
and crestfallen at being baffled by such a small trouble.
CARE OF THE AIR-PUMP.
To run an air-pump successfully, the first requisite is that it should
be managed intelligently, and its wants attended to regularly. An
air-pump consists of numerous moving parts, which should operate with
the least possible amount of friction: consequently, it is important
that the machine should be properly lubricated,--not deluged with
grease for ten minutes, and then run on the interest of the excess
for two hours, but sparingly furnished with clean oil, which will
keep the moving parts moist all the time. To accomplish this, the
feeding-cup must be kept in proper working-order, so that it will pass
the oil regularly. I have found a leading cause for air-pumps working
unsatisfactorily to be in the intermittent feeding of the oil-cups.
Some dirt gets into the cup, obstructing its action, and greater
opening is given to make it feed; then the oil goes through by spasms,
and the pump works irregularly; for at one time the steam-piston is
churning the oil, and again it is working dry. There is also a common
abuse of the oil-can when any thing goes wrong with the pump; for
some men will then drench it with oil, expecting that to make it work
smoothly. Permanent injury is often done in this way, especially where
inferior oils are used, which frequently contain mineral substances in
suspension. This solid matter is separated from the oil by the heat,
and settles in the small passages, filling them up by degrees till
eventually there is no channel left for the steam to pass through to
reverse the steam-valve; so the pump stops. I once saw a runner trying
to doctor a sick pump by pouring the stickiest kind of gummy valve-oil
into an air-cylinder. He gave the thing its quietus, as other poor
doctors sometimes do with their patients.
PUMP PACKING.
The stuffing-box packing is not generally supposed to exercise an
important effect on the action of an air-pump; yet I have seen cases
where irregular action of the pump, and serious loss of air, resulted
from bad packing. Soapstone and asbestos, and other substances that
become compact and rigid when cold, are unsuitable for packing the air
end of a pump. After a little use, material of this kind becomes so
hard that no amount of screwing of the gland will make it tight; and
the greater part of the air at that end of the pump escapes through the
stuffing-box instead of passing into the drum.
HOW STEAM PASSAGES GET CHOKED.
Around the bushings of the cylinder, where the small reversing piston
20 works, are diminutive steam passages, very liable to get stopped up
when foreign matter is attempted to be run through the cylinder. Such
matter is occasionally introduced in various ways. When rubber gaskets
are used in the pipe connections leading to the cylinder, the rubber
often peels off in shreds, or breaks off in small pieces, which lodge
around the bushing in the passages, producing harassing annoyance. So
soon as those passages get obstructed, or reduced below their correct
size, the pump begins to work badly. Machinists not well versed in the
mysterious ways of air-pump disorders will now take that pump apart,
and find nothing the matter. Subsequent proceedings depend upon the
nature of the man who has the job in hand. If the machinist be of a
conservative disposition, he will put the apparatus together again
without making any alteration, and perhaps will relieve his mind by
expressing a belief that the engineer does not know when an air-pump is
in good shape. Another machinist, of a more enterprising stamp, must
find something to change, so he lengthens or shortens the reversing
valve-rod 12 (a favorite resort of small-knowledge tinkers), which
gives the pump the _coup de grâce_; and it has to be overhauled by a
competent machinist before it again supplies the air to stop a train.
This competent man goes direct to the root of the trouble. Skill in
this particular line of work convinces him, after an examination,
that the moving parts require no repairs; and knowledge begotten of
experience, supplemented by sound sense, directs him where to look for
the cause of defective operation.
SAGACITY NEEDED IN REPAIRING AIR-PUMPS.
Men who meet with good success in repairing air-pumps, and in
determining, from the action of the pump, the probable cause of defect,
have to do a great deal of deep and sagacious thinking. Sometimes a
defect, simple enough in itself, is extremely difficult to locate,
because it belongs to the unexpected order of occurrences.
Here was an instance. Some small jobs had been done one day to
the steam cylinder of a pump which had not been working quite
satisfactorily. When they tried to start it, after being put together,
the pump would not work at all. The machinist who did the job, an
eminently competent man at such work, took the machine apart again,
but could detect no defect or maladjustment about it. The steam
cylinder, with all its valves and rods and bushings, was critically
examined: the air-pump, with all its connections, got a thorough
inspection to no purpose. When an ordinary man goes through the
patient, thoughtful labor needed for an examination of this kind, and
finds nothing wrong, he is apt to get discouraged, and confess himself
beaten. This man did not recognize the word beaten as applied to his
work. He reasoned, “This pump would work if it were all right. It will
not work, so something must be wrong.” After exercising more patience
and perseverance, he discovered that the bushing 23 of the reversing
valve (usually called the kicking-rod valve) had become loose, and,
when the cap was screwed down, it twisted the bushing round, and closed
the passages that lead steam to the reversing piston. There are small
grooves round the sides of the small steam passages to provide for the
bushings being moved a little, but these grooves had become gummed up
so that they failed to serve their purpose of keeping the ports open.
GRADUAL DEGENERATION OF THE AIR-PUMP.
The working and stationary parts within the cylinders of the air-pump
are adjusted with nice exactness; and, when they remain in their normal
condition, the pump works smoothly, and compresses air rapidly. When
wear, or any other cause, alters the dimensions of these parts, the
effect immediately becomes apparent in unsatisfactory working of the
whole machine. Rods are adjusted so that valves or pistons shall cover
and uncover steam passages, and no superfluous movement is provided
for. The passages are so small that all the steam they convey is needed
for the work of reversing the motion; and if from any cause the valve
or piston only partly uncovers the opening, the necessary volume of
steam does not get through. A close observer of the pump’s action can,
day by day, perceive the gradual degeneration due to wear. Wear of the
steam-cylinder connections is generally indicated by reduced power. The
pump will not do its work satisfactorily, and has difficulty in keeping
up the pressure of air. This deterioration continues till the pump will
stop, unless its decay gets arrested by repairs. When the valves of the
air-pump are in correct order for doing good work, the discharge-valves
32 and 33 have 1/16″, and the suction-valves 34 ⅛″ lift. The continual
tapping of these valves on their seats has a tendency to wear out
valves and seats, making the lift greater than what is desirable. Any
material increase of lift for the discharge-valve has a most injurious
effect upon the motion of the pump, especially if the suction-valve
should happen to be leaky. Then the movement of the pistons will become
fluctuating, and subject to frequent stoppages. The up-and-down motion
of the piston is of a jerky character, that makes the beholder suppose
the thing is uncertain which way to go. Deterioration of air-valves is
not, however, the only cause for that jerky motion so often observed
in bad working pumps. A bent reversing valve stem (kicker-rod) acts on
the reversing valve with oblique pull and thrust, which tend to move
it away from the seat, letting the steam pass the wrong way. A broken
main steam-valve ring has a similar effect; for the steam passes to
the wrong end of the valve, destroying its equilibrium; and there is
nothing decisive about its reversal, or about its motion after it is
reversed. Its action resembles the movements of a vacillating human
being. It does not want to go in that direction, but goes, then keeps
trying to change its mind during the rest of the journey. Obstructed
steam passages will sometimes cause indecisive action of the pump
before it gets bad enough to stop it altogether.
CAUSES THAT MAKE A PUMP POUND.
Pounding on the heads is a somewhat common attribute of degenerated
air-pumps. Broken or badly worn air-valves very often cause the pump to
pound. If the trouble should happen to be in the upper air-valve, it
will demonstrate its disorder by causing pounding on the upper head;
and the lower valve’s malady will cause pounding on the lower head.
When a pump is suffering from indecisive motion, or is pounding, and
the machinist does not feel certain about where the trouble lies, he
may safely examine the condition of the air-valves,--for they can be
easily reached,--and in a great many cases the defect will be found
there. Wear of the pin whereon the bottom of the main valve-rod rests,
or of the rod itself, will induce pounding on the upper head by the
main piston. Some runners think, that, by keeping the drain-cock of the
steam-cylinder open all the time, they secure dry steam. The practice
is pernicious, and injurious to the pump: for the piston receives so
little cushion when the drain-cock is shut, that it can not afford the
decrease made by a permanently open cock; and consequently the loss of
cushion permits pounding on the lower head.
I have known of a disastrous effect being produced on a pump by putting
a new gasket, which proved too thick, on the upper head. It was the
thinnest copper that could be found, but it perceptibly lengthened the
upper end of the cylinder so that the bottom knob on the reversing stem
struck the reversing plate on the main piston before that action was
due. On several occasions I have had air-pumps reported to be working
badly, when all the trouble lay in the air-strainer being partly
choked up by floating vegetable matter that had been sucked in with
the air, and failed to pass through the meshes. In another case we had
much difficulty in locating the defect, with a pump that absolutely
refused to work. The boiler-makers had been working in the smoke-box,
and by some means the end of the exhaust-pipe got solidly stopped up
with cinders. As none of us had come across that particular cause of
obstruction before, we expended a good deal of labor searching for the
trouble before we thought to disconnect the exhaust-pipe from the pump.
THE TRIPLE VALVE.
This is the part whose operation gives the brake its automatic action.
Those who have opposed this form of brake have made great objection
to the complicated nature of the triple valve. But some familiarity
with the device shows that it is far from being complex, considering
the functions it performs. It is merely a piston-valve carrying a
slide-valve along with it.
The arrangement of the parts of the triple valve is shown in Fig. 34.
[Illustration: FIG. 34.]
The triple valve has a piston 5, working in the chamber _B_, and
carrying with it the slide-valve 6. Air enters from the main pipe
through the four-way cock 13 into the drain-cup _A_, and passes
to the chamber _B_, forcing the piston up, and uncovering a small
feeding-groove in the upper part of the chamber, which permits air
to flow past the piston into the auxiliary reservoir, while, at the
same time, there is an open communication from the brake-cylinder to
the atmosphere through the passages _d_, _e_, _f_, and _g_. Air will
continue to flow into the auxiliary reservoir until it contains the
same pressure as the main brake-pipe.
ACTION OF THE TRIPLE VALVE.
To apply the brakes with their full force, the compressed air in the
main brake-pipe is permitted to escape, when the greater pressure
in the auxiliary reservoir forces the piston 5 down below the
feeding-groove, thus preventing the return of air from the reservoir
to the brake-pipe. As the piston descends, it moves with it the
slide-valve 6, so as to permit air to flow directly from the auxiliary
reservoir into the brake-cylinder, which forces the pistons out, and
applies the brakes. The brakes are released by again admitting pressure
into the main brake-pipe from the main reservoir; which pressure, being
greater than that of the auxiliary reservoir, forces the piston 5 back
to the position shown in the engraving, recharges the reservoir, and at
the same time permits the air in the brake-cylinders to escape.
To apply the brakes gently, a slight reduction is made in the pressure
in the main brake-pipe, which moves the piston down slowly until it
is stopped by the graduating spring 9. At this point, the opening _l_
in the slide-valve is opposite the port _f_, and allows air from
the auxiliary reservoir to feed through a hole in the side of the
slide-valve, and through the opening _l_ into the brake-cylinder.
The passage _l_ is opened and closed by a small valve 7, which is
attached to, and moves with, the piston 5, provision being made for
a limited motion of these parts without moving the valve 6. When the
pressure in the auxiliary reservoir has been reduced by expanding into
the brake-cylinder until it is the same as the pressure in the main
brake-pipe, the graduating spring pushes the piston up until the small
valve 7 closes the feed opening _l_. This causes whatever pressure is
in the brake-cylinder to be retained, thus applying the brake with a
force proportionate to the reduction of pressure in the brake-pipe.
TO PREVENT CREEPING ON OF BRAKES.
To prevent the application of the brakes, from a slight reduction of
pressure caused by leakage in the brake-pipe, a semicircular groove is
cut in the body of the car-cylinder, 9/64 of an inch in width, 5/64
of an inch in depth, and extending so that the piston must travel
three inches before the groove is covered by the packing leather. A
small quantity of air, such as results from a leak, passing from the
triple valve into the car-cylinder, has the effect of moving the piston
slightly forward, but not sufficiently to close the groove, which
permits the air to flow out past the piston. If, however, the brakes
are applied in the usual manner, the piston will be moved forward,
notwithstanding the slight leak, and will cover the groove. It is very
important that the groove shall be three inches long, and shall not
exceed in area the dimensions given above. Heretofore leakage valves
have been used, and also a leakage hole. These leakage holes have been
found to be too uncertain in their operation; and consequently it is
recommended that these holes should be closed, and the grooves in the
cylinders substituted, as rapidly as possible.
When the handle of the four-way cock 13 is turned down, there is a
direct communication from main brake-pipe to the brake-cylinder, the
triple valve and auxiliary reservoir being cut out; and the apparatus
can be worked as a non-automatic brake, by admitting air into the main
brake-pipe and brake-cylinder, to apply the brakes. When from any cause
it is desirable to have the brake inoperative on any particular car,
the four-way cock is turned to an intermediate position, which shuts
off the brake-cylinder and reservoir, leaving the main brake-pipe
unobstructed to supply air to the remaining vehicles.
The drain-cup _A_ collects any moisture that may accumulate, and is
drained by unscrewing the bottom nut.
HOW TO APPLY AND RELEASE THE BRAKE.
The brakes, as has been explained, are applied when the pressure in
the brake-pipe is suddenly reduced, and released when the pressure is
restored.
It is of very great importance that every engineer should bear in
mind that the air-pressure may sometimes reduce slowly, owing to the
steam-pressure getting low, or from the stopping of the pump, or from
a leakage in some of the pipes when one or more cars are detached
for switching purposes, and that in consequence it has been found
absolutely necessary to provide each cylinder with the leakage groove
already referred to, which permits a slight pressure to escape without
moving the piston, thus preventing the application of the brakes, when
the pressure is slowly reduced, as would result from any of the above
causes.
This provision against the accidental application of the brakes must
be taken into consideration, or else it will sometimes happen that all
of the brakes will not be applied when such is the intention, simply
because the air has been discharged so slowly from the brake-pipe that
it only represents a considerable leakage, and thus allows the air
under some cars to be wasted.
It is thus very essential to discharge enough air in the first
instance, and with sufficient rapidity, to cause all of the leakage
grooves to be closed, which will remain closed until the brakes have
been released. In no case should the reduction in the brake-pipe for
closing the leakage grooves be less than four or five pounds, which
will move all pistons out so that the brake-shoes will be only slightly
bearing against the wheels. After this first reduction, the pressure
can be reduced to suit the circumstances.
On a long train, if the three-way cock be opened suddenly, and then
quickly closed, the pressure in the brake-pipe, as indicated by the
gauge, will be suddenly and considerably reduced on the engine, and
will then be increased by the air-pressure coming from the rear of the
train: hence it is important to always close the three-way cock slowly,
and in such a manner that the pressure, as indicated by the gauge, will
not be increased; or else the brakes on the engine and tender, and
sometimes on the first one or two cars, will come off when they should
remain on. It is likewise very important, while the brakes are on, to
keep the three-way cock in such a position that the brake-pipe pressure
can not be increased by leakage from the main reservoir; for any
increase of pressure in the brake-pipe causes the brakes to come off.
On long down grades, it is important to be able to control the speed of
the train, and at the same time to maintain a good working pressure.
This is easily accomplished by running the pump at a good speed, so
that the main reservoir will accumulate a high pressure while the
brakes are on. When, after using the brake some time, the pressure has
been reduced to sixty pounds, the train pipes and reservoirs should
be recharged as much as possible before the speed has increased to
the maximum allowed. A greater time for recharging is obtained by
considerably reducing the speed of the train just before recharging,
and by taking advantage of the variation in the grades.
There should not be any safety-valve or leaks in the main reservoir,
otherwise the necessary surplus pressure for quickly recharging can not
be obtained.
To release the brakes with certainty, it is important to have a higher
pressure in the main reservoir than in the main pipe. If an engineer
feels that some of his brakes are not off, it is best to turn the
handle of the three-way cock just far enough to shut off the main
reservoir, and then pump up fifteen or twenty pounds extra, which will
insure the release of all of the brakes; all of which can be done while
the train is in motion.
For ordinary stops, great economy in the use of air is effected by, in
the first instance, letting out from eight to twelve pounds pressure
while the train is at speed, taking care to begin a sufficient distance
from the station.
PUMP GOVERNOR.
This is an important attachment which ought to be connected to all
air-brake pumps. It not only prevents the carrying of an excessive
air-pressure by the engineers, which often results in the sliding
of the wheels, but it also causes the accumulation of a surplus of
air-pressure in the main reservoir, while the brakes are applied, which
insures the release of the brakes without delay. It also limits the
speed of the pump, and consequently the wear.
[Illustration: FIG. 34_b_.]
The pump governor is shown in Fig. 34_b_, the object of which is
to automatically cut off the supply of steam to the pump when the
air-pressure in the train-pipe exceeds a certain limit, say seventy
pounds.
The operation of this governor is as follows: the wheel 8 is screwed
down so as to permit the valve 10 to be unseated by the excess of
pressure on the upper side of the valve, permitting steam to pass
through the openings _A_ and _B_ to the pump. A connection is made from
the train-pipe to the upper end of the governor, and the compressed
air passes around the stem 14 to the upper side of the diaphragm plate
18, which is held to its position by the spring 16, which latter is of
sufficient strength to resist a pressure of, say, seventy pounds per
square inch on diaphragm. As soon as the air-pressure on the diaphragm
18 exceeds this amount, it forces the diaphragm down, unseating the
valve 13, and allowing the steam on the upper side of the valve 10 to
escape through the exhaust 6, which causes an excess of steam-pressure
on the lower side of the valve 10, forcing the valve against its seat,
and cutting off the supply of steam to the pump.
When the pressure in the train-pipe is diminished by applying the
brakes, the diaphragm is restored to the position shown by the action
of the spring 16. The valve 13 is seated by the spring 12; and the
steam-pressure, passing through the port _C_, accumulates on the upper
side of the valve 10, forcing it down, and opening the passage for
steam to the pump until the air-pressure is again restored to the
required limit of seventy pounds.