BASIC COURSE OF

AIR BRAKE
compressed
RAILWAY
 ORIGINS AND DEVELOPMENT OF COMPRESSED AIR BRAKES
RAILWAY

One of the main factors for the development of rail transport was,
Without a doubt, the invention and use of the compressed air brake. Besides the safety that this
the type of brake came to represent, it became possible to increase the number of vehicles
by train, the capacity of the wagons, as well as the operating speed of the fleet.
Before the use of compressed air brakes, the cargo compositions in
The United States were limited to about ten wagons with approximately 18.
ton. of capacity, traveling at a speed of 15 to a maximum of 25 km/h.
In this way, it is easy to deduce that the prospects for the railways for the
the future was seriously compromised, since, with limited trains in
weight and speed, along with the lack of safety and operational difficulties, made it
unfeasible the high investments for construction, maintenance, acquisition of
rolling stock, etc., involved in the operation of a railway.
Regarding the lack of security, one only needs to remember that in the United States, there were
an alarming rate of accidents, with American railways in the year 1850
killed, on average, one passenger for every 200,000 transported.
Until the year 1869, controlling the decrease in the stopping speed of a train in
a ramp was a true adventure.
To request the brakes, the engineer would give a whistle, as pre-established,
which could mean reduction of speed, normal stop or emergency stop.
After conveniently interpreting the whistle, the brake guards, positioned over the
wagons, they ran and operated the manual brake wheels.
Each brake guard was responsible for the operation of the brakes and condition of
maintenance of the wheels of two wagons, (sometimes even four), at the end of the operation
the engineer applied a 'back steam' and the train stopped, with a lot of luck, close to
desired location.
For an emergency stop, things got more complicated: the engineer
devia apitar para alertar os guarda-freios, atuar os freios manuais do "tender" e aplicar
to the maximum 'against steam'.
If any brake guard, by luck, still stood upright, it should press the
brake lever of the largest number of cars possible. This way it is possible to evaluate
how the railway accidents of that time were not only frequent but also fatal for the
Passengers and burdensome regarding the loss of rolling stock.
In addition to the brakes operated by wheels, some railways, American
they also operated with locomotives equipped with steam-operated brake cylinders. This
invention (1833 - 1834) by George Stephenson, however, was not effective.
mainly due to the loss of efficiency at lower temperatures.
Nehemiah Hodge patented the vacuum brake in 1860 in the United States.
for locomotives and cars.
The vacuum brake system basically consists of a brake cylinder.
installed in each vehicle and connected to the main plumbing, which is the plumbing that

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passes through all the vehicles of the composition and goes up to the locomotive, having its
continuity guaranteed by flexible hoses.
The general plumbing is the element that has a dual function of ensuring the means by
where the evacuation of all cylinders of the composition is done and through which,
reduction of the initial vacuum degree present in it, the control of the formation of
pressure in the brake cylinders of the composition.

When one wants to relieve the brakes, a vacuum is created in the main piping and it is
it is possible then to create a vacuum in both chambers of the cylinder: in the lower one, directly and
at the top, through the check valve (fig. 1).
To apply the brakes, atmospheric pressure is allowed in the main piping and
consequently in the lower chamber of the cylinder. Then a differential arises
pressure capable of making the piston rise (fig. 2).
The vacuum brake system is said to be automatic because when there is a break in
train with the consequent discontinuity of the main piping, the air of the atmosphere

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penetrating, through the opening produced in the main plumbing, applies the brakes of both
the parts of the train.
In the vacuum brake system, atmospheric air pressure is used to generate the
force that makes the brake shoes act against the wheels.
However, the low pressure achieved in practice with this type of equipment, 7 to 8
psi., caused primarily the vacuum brake chambers or cylinders to be
too large and heavy in order to achieve braking force
necessary.

Another problem with vacuum brakes was the loss of their efficiency as
started operating in higher places.
In 1869, George Westinghouse invented the compressed air brake which came to
from then on, improve the safety and operation conditions of railways across all
world.
On April 13, 1869, George Westinghouse made the first demonstration.
practice of the new brake system.

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 The experiment took place on the Pennsylvania Railroad, between Pittsburgh and
Stenbenville, on a steam locomotive coupled to a pair of passenger cars.
The compressed air braking system initially operated in a way
similar to the vacuum brake system, that is, it consisted of a brake cylinder
installed in each vehicle and connected to the piping that runs through all the vehicles
from the composition and goes to the locomotive, having its continuity guaranteed by
flexible hoses. This system was called Direct Air Brake.

DIRECT AIR BRAKE

In the air brake system, the agent used to generate the necessary force to
Applying the brake shoes against the wheels is compressed air.
The compressor that, at that time, operated with steam, is the organ that
provides compressed air for the brake system operation. To obtain this air,
The steam, through a device, is admitted, now into chamber 'A', now into chamber 'B'
of a piston, transmitting this movement to a cylinder. In the movement
descending from the piston (fig. 3), the air contained in chamber 'D', whose volume is being
decreased, begins to increase its pressure and then is discharged by the
bottom flush valve for inside the main reservoir. This same
movement, executed by the piston, causes the air from the atmosphere to be admitted
through the upper intake valve, into chamber 'C' of the compressor.
When the piston starts its upward movement, the upper intake valve is
closed by the action of its spring and the air begins to be compressed inside chamber 'C'
and the increase in pressure opens the discharge valve flowing into the reservoir
main. With the three-way valve in the closed position, this movement of the piston
will create pressure inside the main reservoir. This position is known as
from the "Relief Position", this is because the air from the brake cylinders of the entire train remains
connected to the atmosphere through the three-way valve (fig. 3).
When one wishes to apply the brakes, air is introduced into the main piping.
compressed contained in the main reservoir, by turning the handle of the three-way valve
ways to the application position. In this position, known as 'Position of
"Application", the air will reach the brake cylinders in each vehicle of the composition, and
will overcome the pressure of the spring on its side without pressure and will move the piston
applying the brakes against the wheels, (fig. 4). To relieve the brakes, the engineer
I raised the three-way faucet lever to the relief position, in which it promoted
the discharge of all the main plumbing into the atmosphere, thus exhausting it,
pressure of all brake cylinders. Under the action of their springs, the pistons of the
cylinders returned to their original position relieving the brakes of the whole train.
During the relief, the three-way tap isolated the supply system from
in the compressed air of the train's main pipeline. The direct air brake was already widely
used in the United States, coast to coast, around 1871.
However, despite its simplicity, the direct air brake also limits the

4
size of the compositions and the collision problems between the carriages resulting from the
high application times and brake relief, still presented the great inconvenience
not to be safe, in case the main pipeline of the train were to break. In this case, not
braking the entire composition.
In order to eliminate the deficiencies of the direct air brake, Westinghouse developed
he patented the first automatic air brake equipment in 1872, as we will see
in the following chapters.

BASICS OF BRAKING TECHNIQUE.

- GENERALITIES -

Before we get into the brake part

In Automatic, let's look at some foundations of
braking technique.
FRICTION - The braking of a
railway vehicle is obtained by the application
of cast iron or materials
non-metallic against the wheels or against
solidarity discs with her.
The kinetic energy that the vehicle
is then converted into heat by the
friction of the brake pad against the wheel, and it is dissipated
to stop the vehicle or reduce its
speed.
The forces acting on the wheel during braking are shown in fig. 5 and
they are the following:
F1 = braking force applied to each brake shoe of the wagon.
F2 = tangential force developed on the surface of the wheel, due to the action of
F1
F3 = force existing between the surfaces of the wheel and the rail, and that allows
the rotation movement of the wheel. This force is due to the adhering weight, that is, to the weight
of the vehicle on the tracks, and it is called adhesion.
For a perfect braking, it is necessary for the vehicle to stop with
the wheels turning, because if they stop doing so;
a) the grip decreases, the vehicle slips and escapes the control of the brakes.
b) calluses form on the wheels
For the above condition, we must have F2 < F3 (1), because then the conjugate that
keeping the wheel turning will always be greater than what tends to stop it.
However, F2 = F1 x a (2) where 'a' is the coefficient of friction between the shoe and the wheel, and F3
Pa x b where 'b' (3) is the coefficient of friction between the wheel and the rail

7
 These coefficients are variable due to the influence of several factors, such as the
speed, humidity, temperature, surface conditions, etc.
However, the most predominant influencing factor is the speed coefficient.
of friction 'a' between the shoe and the wheel, and speed and humidity for the coefficient of friction
"b" between wheel and rail.
Figure 6 shows the curves of variation of 'a' with speed and of 'b'.
with the speed and humidity (state of the tracks).
Taking into account equalities (2) and (3), equation (1) takes the following form.
aspect:

b
F1 < Pa
a

which will theoretically give us the braking effort F1 to be applied at each

wheel of a vehicle weighing Pa per wheel.
Meanwhile, the determination of the braking effort by this formula, directly,
it is difficult to execute in practice, once
that the coefficients 'a' and 'b' are of
complicated determination, due to the
various factors that influence them.
Thus, what is done in practice
railway for determining the efforts
of braking to be used in the various
types of vehicles, is to use practical rules,
resulting from experiments, whose objective is
ensure the safety of trains and prevent the
wheel slip.
The adhesion coefficient varies with
the nature of the surfaces in contact (type
of the materials), with their condition
existence or non-existence of foreign matter
interposed), with the atmospheric conditions and
with speed.
Rough surfaces present
higher coefficient of friction than the
lisas. Thus, the adhesion coefficient of
tire on the rough pavement is
0.40 to 0.50 (40 to 50%), while on smooth surfaces it is 0.25.
The coefficient of friction of steel wheels on steel rails has the following
approximate values:
Completely dry trail or washed by rain 0.33
Dry and clean trail 0.22
Dry trail 0.20
Wet trail from the rain 0.14
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 Dew wet trail 0.125
Wet and dirty trail 0.11
Track with oil 0.10
In practice, a mean value of 0.22 is usually taken for traction calculations.
for the dry rail adhesion coefficient.
The low adhesion coefficient for the dew-wet rail is explained by the
in the following way: a film of dew, reaching a part of the ticket dirty with oil,
even dry, due to the phenomenon of surface tension causes the oil to advance,
forming an oil film that lubricates the head of the rail, (ticket)
decreasing adherence,(Fig. 7).

BALANCE -RESERVOIRS -
And brake cylinders

The balance between the two volumes with

different pressures is obtained with the connection between
them, allowing the airflow until both
they are under the same pressure. The pressure of
equilibrium depends on the size of the volumes
connected and their original pressures.

RESERVOIRS WITHOUT CONNECTION

The illustration on the side shows reservoirs

not connected with various volumes.
loaded and under pressure. Those shown to
the left side has constant volumes and are
loaded at 70 lbs/sq in gauge and those of
right, without pressure but with various volumes. In the illustration, the two above
they have the same volume; in the center, the one on the right is smaller than the one on the left and;
the one on the right is bigger than the one on the left

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 CONNECTED RESERVOIRS

When these reservoirs are connected the

The air flows from the loaded to the empty until equilibrium.
The two whose volumes are identical if
they will balance with the pressure at half of the original. If
the pressure was 70 lbs/in² the equilibrium will be at 35
lbs/in²
When the two reservoirs are different
volumes are connected, with one loaded and the
empty outcome, the result of the balance may be
greater or less than half of the pressure of
loaded. The balance between both depends on the
comparative proportion of the volumes of
reservoirs. If the volume that is empty is smaller
that when loaded, the balance will be above average
and, in the case of the latter being greater, the pressure will be
younger.

BRAKE CYLINDERS
The first illustration next to shows an auxiliary reservoir connected to a
brake cylinder. The volume of the reservoir is such
that, when the brake cylinder reaches its
correct course, the pressure of 70 lbs/in² if
it will balance at exactly 50 lbs/in² when it is
the connection between both was made.
The second illustration shows the same
reservoir with 70 lbs/in² connected to a
same brake cylinder, however, with a stroke
menor que o normal. A pressão de equilíbrio
(in this case 60 lbs/in²) will be something between the
initial loading pressure of the reservoir
auxiliary (70 lbs/in²) and the equalization between
this is the brake cylinder with normal stroke (50
lbs/in².
The third illustration shows the same.
auxiliary reservoir loaded with 70
lbs/pol² is connected to the same brake cylinder,
however, with a course above normal. The
equilibrium pressure (in this case 40 lbs/in²)
it will be slightly below the correct pressure (50 lbs/in²)
depending on how much the cylinder's course of
the brake is above normal.

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 DISPLACEMENT

Displacement (in relation to air brakes) is the change that occurs in a

cylinder, reservoir, diaphragm or other means.
The displacement of the brake cylinder is the change in cubic measurement of the volume
when your piston reaches the full stroke, compared to the initial volume in the position of
relief.

When the brake cylinder piston moves from the relief position to
application, the volume of the cylinder (the side where the pressure is being built) is
increased as the pressure, without additional air supply, would be reduced.
Thus, the brake operation is such that the air is always supplied, this means
what additional pressure should be provided to achieve proper equalization
due to this loss through the
displacement.

The brake cylinder is a

reservoir where one of its walls
moves. In the relief position,
being your supply line
linked to the atmosphere, the pressure
against your piston will be zero
manometric or atmospheric. See the
illustration above.

The supply passage is

so closed, as shown in the figure
next. The rod of the cylinder is fixed to the
brake lever and with the fixed point
in the center, a force is applied to the other
end in such a way that the piston
move to the position of
application.

Let's admit that there is no

no leaks in the connections and
no pressure. If a suitable manometer is installed in the cylinder, it will indicate a
pressure less than zero (or atmospheric) and, as an illustration, let's say it is 8.5
negative lbs/pol².
If it weren't for this displacement, 5 lbs/in² of the auxiliary tank pressure
they would give approximately 12.5 lbs/in² in the brake cylinder, but with the displacement
for the piston, the trend is to reduce this value to approximately 4 lbs/in², which
means a loss of 8.5 lbs/in².

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 The cylinder's supply after the first 5 or 10 lbs/in² will be a growth
from 2.5 lbs/in² to every 1 lbs/in² from the auxiliary reservoir outlet as long as the stroke
comply with the specific standards for each type of wagon equipment. In
In practice, the following formula is commonly used for the approximate calculation of pressure of
brake cylinder, starting from the reduction made in the general plumbing:

Pcf = 3.25R - 15 where:

Pcf - Pressure in the cylinder of
brake
R - Reduction in piping
general mind
15 - Atmospheric pressure
rounded from the value of
14.7 Ibs/pol'
3.25 - Relationship between the
volumes of the auxiliary reservoir and
brake cylinder in position
application and with course within value
correct. Example. What is the pressure?
in the brake cylinder after a reduction in the general piping of 12 lbs/in²
3.25 x 12 - 15
Pcf = 24 lbs/in²
TRIPLE VALVE
The control valve was known
as a triple valve because it had three functions
basics:
1. Load the auxiliary reservoir of the
carriage
2. Apply the brakes;
3. Release the brakes.
The triple valve is the core of any
Westinghouse air brake system, except in the
more modern.
It basically consists of:
a) A piston with a rod, having a sealing ring mounted in a groove on it
existing.
b) a metering valve attached to the piston rod that follows all the
your movements, sliding over a thirst, against which it is held, by the
action of a spring.
c) A gate valve that is held by the pressure of a spring against a
existing seat in the triple valve bushing. In the gate valve, it remains
also the seat of the adjusting valve.

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 The gate valve is dragged by the
piston in its movements due to a
"tooth" existing in your stem, however there is
a break that allows for a displacement
of the piston/graduator set, without the
gate valve moves.
The basic components of the valve
triplet is shown in fig. 8.
We move on to the examination of the three functions.
of this valve, following them in the diagrams
reproduced below:

a) Loading: (fig. 9a) - The air

from the supply system
from the locomotive's compressed air, flowing
through the main plumbing, acts on the face
the piston moving it to the right,
then the loading of the
auxiliary pressure reservoir
general plumbing through the groove of
food.

b) Preliminary service position

(fig. 9b) - When a reduction is made of
pressure in the main piping, to start
a brake application, the pressure drop
verified on the piston face, on the side of the
general plumbing, causes the movement
initial of the piston to the left until
your top rod in the gate valve. This
movement will close the slot of
food shutting off the plumbing
general of the auxiliary reservoir and will connect the air
from the auxiliary reservoir to the headquarters of the
gate valve.
c) Position of service application
(fig 9c) Continuing the reduction in
general plumbing creates a differential
among the pressures acting on the faces
of the piston related to the main piping and auxiliary reservoir, capable of overcoming the
friction of the gate valve and its seat and move the assembly to the left, until the
piston hits the stabilizer spring rod. At this moment, the air from the reservoir
the auxiliary will be connected to the brake cylinder, creating pressure inside it.

13
 d) Coating (fig. 9d) - Once the reduction of pressure in the piping has ceased
Generally, if a complete service application has not been made, the air will continue to flow from the
auxiliary reservoir for the brake cylinder, until it becomes slightly less than
pressure acting on the other side of the piston. There will then be a difference between the
pressures acting on the faces of the piston
regarding the general plumbing and
auxiliary reservoir, capable of displacing
the piston/valve regulating set
to the right and this last one closes the
passage through which communication was made
auxiliary reservoir with the cylinder of
brake, stopping the flow from the first to
this last one.

e) Reloading and relief (fig.

9e) - For brake relief, it is done
increase the pressure in the plumbing
general and again the difference between the pressures acting on the faces of the piston
related to the main plumbing and auxiliary reservoir that will move the set
piston/gate valve for the right end. In this position, the
reloading of the auxiliary reservoir through the feed slot and will be
established the connection of the brake cylinder with the atmosphere. The existing spring in the
chamber without pressure from the brake cylinder will cause the piston to return to its
relief position.
In addition to the service application
intended to stop or reduce the
train speeds under conditions
normal, it was necessary to introduce
an emergency application for
faster stops in the cases of
eminent risks of fatal accidents or
give us materials of great value.
These quicker stops were
initially obtained with the growth
but faster the pressure in the cylinder and
subsequently, combined with an increase
of the value of the final pressure obtained there, with the introduction of a supplementary volume in
each vehicle, called emergency reservoir.

Emergency application (fig. 9f) - To obtain an application of

in an emergency, the pressure in the main piping is reduced at a rate

14
faster than the normally used for the reduction aimed at producing
service applications.
In these conditions creates oneself
quickly a pressure differential
able to overcome the friction of the set
piston/gate valve and resistance of
stabilizing mole, allowing for
direct communication from the reservoir
assist with the brake cylinder by a
wider passage, giving then the
faster growth of pressure in
brake cylinder.
The stabilizing fin was
introduced into the triple valve for
guarantee differentiation in your operation
according to the rate of pressure drop in the main piping.
The intensity of brake application was proportional to the drop in pressure that the
mechanic, through the three-way tap, caused in the general piping. The
maximum braking intensity was obtained when the volume of the auxiliary reservoir and
brake cylinder was in equilibrium.
The use of automatic braking allowed for faster action and
safe operation of longer trains, with compositions of up to 30 becoming common
wagons.

FEEDING VALVE:

At the same time they were modernizing the

válvulas de controle (válvulas tríplice) foram sendo
refined and created the other devices of the
train brake system.
In 1880, the valve was developed.
nutrition, for blood pressure control
general plumbing.
With it, one could easily regulate the pressure.
in the general plumbing with desired values (70,
80, 90 psi
Large pressure reducing valves
sensitivity and capacity that supplies the
general compressed air piping at a pressure
regulated, through the three-way tap or
automatic brake manipulator. It must be adjusted

15
at least 70 lbs/sq in or according to the standards set by the railway.
The oldest types were separate sets, whereas nowadays they are integrated.
the automatic manipulator itself.

OPERATION:

In fig. 10, with the adjusting screw

release all the air from the main reservoir to a
pressure of 125 to 140 lbs/sq.in comes through the passage
"IN" of the feed valve and is retained in the
spherical supply check valve
inferior.

In this position, the spherical flush valve

the superior remains away from its headquarters linking the
to the passage 'OUT' to the atmosphere together
with the diaphragm air of the valve. Therefore, it
start the valve adjustment by turning the
adjustment screw clockwise, the
spring set and diaphragm follower and diaphragm
will move, initially allowing the
closing of the upper ball valve - valve
of discharge - disconnecting the chambers and passages already described from the atmosphere. (fig. 11)

In the sequence of adjusting the screw, the assembly will allow the opening of the
lower ball valve - for supply - allowing air from the reservoir
the main one starts to flow into the general piping. At the same time, this air will be
acting through a restricted orifice, in the part
inferior of the diaphragm of the feeding valve. The
main reservoir pressure, thus, will
going to the general plumbing of the train
load the auxiliary reservoirs of all the
train cars of the composition.

When the pressure throughout the plumbing

general and auxiliary reservoirs, of the train that
is also acting on the diaphragm area of the
feeding valve to overcome the force exerted
through the spring over the diaphragm, the set will
move up allowing the lower sphere
supply valve - should be installed over the
your thirst, no longer allowing the air of
main reservoir passes to the plumbing
general.
In this position, the upper sphere - valve
download - will also remain closed in your
it does not allow the flow of air to the atmosphere
16
 Any modification that may occur in
The pressure of the main plumbing will be reflected.
at the bottom of the diaphragm of the valve
nutrition. If there is an increase in pressure
above the force exerted by the spring the set
diaphragm/follower will open the upper sphere -
flush valve - from its seat discharging the
excess pressure for the atmosphere.
In case of a drop in pressure in the lower chamber of
the diaphragm or assembly will move downwards and the
lower sphere - supply valve - will be
open feedback to the system

AUTOMATIC AIR BRAKE.

The term "automatic" was due to the fact that this new system applied the
brakes on all cars, regardless of the engineer's action, in case of a
hose were to break. The operating principle of this automatic system
was based on the fact that the decrease in pipe pressure was the promoter of the
application of the brakes along the train. On the other hand, the increase in pressure of the
The general plumbing caused the release of the brakes.
To implement this new system, it was necessary to reverse the assembly of
three-way faucet in relation to the direct air brake system.
The air intended for the brake cylinders was stored in the auxiliary reservoir.
on the occasion of loading. This reduced the time for applying the brakes,
for the air supply of the cylinders was already present in the wagon itself, not being
it is necessary to wait for its arrival from the locomotive's reservoir.
In this way, the new braking system introduced a valve in each vehicle.
of control and an auxiliary reservoir, maintaining the same brake cylinder of the
previous system.
Next, we will study the positions that the control valve assumes based on
the positions of the brake manipulator (three-way tap).

GEAR POSITION:

In this position, also known as 'Relief and Loading Position'

(fig. 14), the air coming from the compressor is stored in the main reservoir and in
followed through the feed valve and brake handler that is located in
marching position (open), reaches the general piping of the locomotive and, through
flexible hoses, the one from the train.

17
 In the locomotive and in each car there is a branch that directs the air to the valve of
control going to act on the external face of the piston. This, in turn, will move to the
far-right discovering the feed slot loading the reservoir
assistant with the same pressure as the main piping, that is, the one for which the
The feed valve has been adjusted. In this position of the control valve, its
the drawer will be connecting the brake cylinder to the atmosphere.
With no pressure inside it, the brake cylinder will be displaced to the
relief position due to its return spring action.
Under these conditions, the application force of the brake pads is neutralized.
against the wheels. The system will be fully loaded when the last car of a
composition is with the auxiliary reservoir at the same pressure as the
general plumbing or close to this as we will study later.

SERVICE APPLICATION POSITION

When one wishes to apply the brakes of a train, the

The brake manipulator handle must be moved to the application position.
Nessa posição a pressão do reservatório principal que estava ligado para o
main plumbing through the feed valve is interrupted at
brake manipulator. At the same time, it establishes the connection of the piping
general with the atmosphere through a controlled orifice. This will cause a decrease in
pressure of the main piping along the entire length of the train. At the control valves
(locomotive and cars) as soon as the drop in pressure is detected on the piston face,
side of the main piping, causes its movement to the left until the bump
from its top stem to the gate valve. With this, the piston closes the groove of
feeding disconnecting the auxiliary reservoir from the main plumbing. Being the valve
solidarity graduator to the piston its sliding over the gate valve,
provides for the opening of a passage connecting the air from the auxiliary reservoir to the
your thirst. This movement known as 'Service Preliminary' (fig. 15) does not
move the gate valve so the brake cylinder remains connected to
atmosphere.
Continuing the discharge of the main pipeline, the increase in the differential of
pressure will create a force capable of dragging the piston assembly and valve
slide valve (fig. 16). At that moment, the slide valve disconnects the brake cylinder from the
atmosphere. This movement will be limited until the smaller rod on the left side of the
piston touches the stabilizer spring rod. The pressure differential would increase the
point of compressing the stabilizer spring is at this moment the air from the reservoir
the auxiliary would not be drained into the brake cylinder through a hole
controlled at the gate valve. This in turn, receiving the pressure, will displace
providing for the application of the brakes.
This is the so-called 'Service Application Position' which will be greater
the more the brake lever handle is kept in the application position.

18
RECOVER POSITION AFTER A SERVICE APPLICATION

If the reduction of the general piping pressure falls below what allows
the balance between the auxiliary reservoir and brake cylinder, we will then have the position
of receipt (fig. 17) as follows:
Raising the brake lever to the closed position
will stop the discharge of the main plumbing to the atmosphere. The pressure on the outer face
The piston of the control valve, on the side of the main piping, will be stabilized. A
the pressure of the auxiliary reservoir acting on the opposite side of the piston will continue to be
reduced once it is connected to the brake cylinder through the valve seat
graduator and gate valve. At the moment this pressure difference is
capable of producing a force sufficient to overcome the friction of the piston and valve
the graduator will move to the right and the graduator will close
passage that connected the auxiliary reservoir to the brake cylinder. We will then have the
covering position.

Brake relief after a service application

After a service application wishing to relieve the brakes, the handle of the
brake manipulator must be moved to the drive position. In this position, the air
the main reservoir will be connected to the general plumbing through the valve of
feeding. As soon as the pressure on the outer face of the control valve piston
become slightly higher than the pressure of the auxiliary tank it will move
to the right carrying with it the adjusting and sliding valve. With this
the movement will open the feeding slot allowing for recharging
from the auxiliary reservoir and simultaneously the cylinder will be connected to the atmosphere.
through the gate valve. We will thus have the brake relief

EMERGENCY APPLICATION POSITION

In this position, the brake lever's grip should allow a release.

quick release of the general pipeline pressure of the entire train to the atmosphere (fig 18). In the
control valves this sudden drop will cause the set
piston/drawer/graduator move to the far left position compressing the
stabilizing tank. The auxiliary reservoir will then be connected to the brake cylinder by
a wide passage behind the gate valve in its housing. In the position of
in an emergency, the speed of the application will be greater than that obtained in the applications of
service.

RELIEVING THE BRAKES AFTER AN EMERGENCY APPLICATION

To relieve the brakes after an emergency application, proceed with the

same way as described in the Brake Relief Position After An Application

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of Service excepting that in this position the general plumbing was unloaded
zero and the pressure will have to be increased until it exceeds the reservoir pressure
assistant, so that the brakes can be relieved.

MAIN FACTORS THAT INFLUENCE MANIPULATION OF

BRAKES OF A TRAIN
GRADIENT LEAKAGE AND BRAKE CYLINDER COURSE

Leakage - It is the loss of air from the main pipeline of a train. The places
but more prone to this loss are in the connections, taps, couplings between
hoses, etc. The important thing is to reduce this leakage to the minimum possible,
a way that never exceeds five pounds per square inch per minute (5
lbs./pol.²/ min.). The excess leakage greatly affects the handling of the brakes,
as we have seen before, braking applications are obtained by reduction
gradual reduction of the pressure in the general plumbing system. One of these reductions that would have been made
to reduce the speed of a train, it can be stopped if there is an excess of it
leakage. In order to avoid this unwanted stop of the train, the engineer is required to
release the brakes, however, if immediately after the release there is a need to reapply the brakes
brakes, he will not be able to do it since there wasn't enough time for a
minimum brake system reloading, due to the applications made
previously, and still, because the recharge is affected by the leakages.
As we could observe, the pressure loss due to leakage, in addition to
Deregistering the train driver's operations requires even more work from the compressor.
The most modern brake equipment has a set called
"Mantenedor de Pressão", que elimina a aplicação dos freios por vazamento no
general plumbing, as long as it is within the limits of its operation or rather
five pounds per square inch per minute (5 lbs./in²/min).
The leak is the biggest provocateur of gradient.

Gradient - We call gradient the pressure difference in the piping.

general between the locomotive and the last car of a train, and this should not exceed 10%
of the total number of vehicles in the composition, that is: for every ten vehicles of one
trem may exist a difference of one pound per square inch
(1lbs./pol.²/min) between the locomotive pressure and the last car of the train.
While the leak increases, the application of the brakes renders the gradient impossible.
the application of brakes in the latest vehicles. The current control valves are
equipped with a device capable of compensating for the deficiencies worn out by excess
gradient.
This device is known as a Quick Service Limiting Valve.

Brake cylinder stroke - We call it brake cylinder stroke

distance that your piston moves when it receives pressure, in order to imprint
effort in the brake steering. With the wear of the wagon brake shoes, the course

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the brake cylinder increases, decreasing the pressure inside it, consequently
reduces the shoe's effort against the wheels.
The volume of the brake cylinder, which is supplied with air from the reservoir
assistant, depends directly on your course.
Thus, if we want to achieve a uniform braking effort on each vehicle, it is
I need the courses of your brake cylinders to be uniform.
On the same train, if there are various brake cylinder courses, there will be
collisions and jolts between vehicles, which may cause jaw fractures
bumper or even derail the train. With technological development
automatic adjusters were introduced in the brake hardware (steering gears)
Play, which can be pneumatic or mechanical functioning, but with only one
Purpose: to maintain the brake cylinder stroke of the wagons at a single pre-determined value.
established.
There are different standards for the various types of brake cylinders.
However, we must follow them according to the technical specifications

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