28-01-2012, 11:54 AM
Vaccum Brake System
The vacuum brake is a braking system employed on trains and introduced
in the mid-1860s. A variant, the automatic vacuum brake system, became
almost universal in British train equipment and in those countries influenced
by British practice. Vacuum brakes also enjoyed a brief period of adoption
in the USA, primarily on narrow gauge railroads. However, its limitations
caused it to be progressively superseded by compressed air systems starting
in the United Kingdom from the 1970s onward. The vacuum brake system is
now obsolete; it is not in large-scale usage anywhere in the world,
supplanted in the main by air brakes.
Moving train contains energy, known as kinetic energy, which
needs to be removed from the train in order to cause it to stop. The
simplest way of doing this is to convert the energy into heat.
The conversion is usually done by applying a contact material to
the rotating wheels or to discs attached to the axles. The material creates
friction and converts the kinetic energy into heat. The wheels slow down
and eventually the train stops. The material used for braking is normally in
the form of a block or pad.Vacuum brakes were a big step forward in train
safety.
Overview
In the earliest days of railways, trains were slowed or stopped by the
application of manually applied brakes on the locomotive and in brake
vehicles through the train, and later by steam power brakes on locomotives.
This was clearly unsatisfactory, but the technology of the time did not easily
offer an improvement. A chain braking system was developed, requiring a
chain to be coupled throughout the train, but it was impossible to arrange
equal braking effort down the length of the train.
A major advance was the adoption of a vacuum braking system
in which flexible pipes were connected between all the vehicles of the train,
and brakes on each vehicle could be controlled from the locomotive. The
earliest pattern was a simple vacuum brake, in which vacuum was created by
operation of a valve on the locomotive; the vacuum actuated brake pistons
on each vehicle, and the degree of braking could be increased or decreased
by the driver. Vacuum, rather than compressed air, was preferred because
steam locomotives can be fitted with ejectors, which are simple devices that
create vacuum without the use of moving parts.
However, the simple vacuum system had the major defect that
in the event of one of the hoses connecting the vehicles becoming displaced
(by the train accidentally dividing, or by careless coupling of the hoses, or
otherwise) the vacuum brake on the entire train was
How they work :
The brakes themselves are in the form of metal shoes which press against the
train's wheels creating friction which slows the train down.
On a train equipped with vacuum brakes, every wagon or coach is equipped
with at least one set of brakes. The default position of each brake shoe is on
and the brakes are spring-loaded so that without vacuum, there is pressure
applied. Behind each brake shoe is a vacuum cylinder which contains a
piston, which draws the brake shoe forwards or backwards, or into the on or
off positions.
An airtight pipe runs along the entire length of the train. The air is pumped
out of this pipe by a pump in the locomotive to form a vacuum. As a vacuum
forms in the vacuum cylinder behind the piston, the piston is pushed
backwards by atmospheric pressure, thereby drawing the brake shoe
backwards into the off position.
The brakes will automatically move forward to the default "on" position if
the vacuum is broken. The train driver can apply the brakes by opening a
valve which lets air into the pipe thus breaking the vacuum. If the train
breaks up or the pipe develops a leak, the vacuum will again be broken and
the brakes will come on.
The vacuum brake was considered preferential to the air brake in railroad
applications largely because it was cheaper to install on a steam locomotive.
Air brakes required a steam-powered compressor - bulky, noisy, unsightly
and using a lot of power, while the vacuum ejector used to generate vacuum
was a much simpler device, having no moving parts.
MAINTENANCE AT WORKSHOP:-
During POH all components of the brake
gear system shall be examined, repaired and
replaced as necessary. The pins and bushes
shall be examined for wear and replaced if
the radial clearance exceeds 0.75 mm.
Following items should receive particular
attention during POH:
i) Safety brackets provided for brake gear
components should be in accordance
with the approved drawings and shall
be examined for proper condition and
secured according to the prescribed
method.
ii) Vacuum cylinders and their trunnion
brackets, vacuum reservoirs and train
pipes, rubber hose & syphon pipes,
alarm chain apparatus including the
chain, disc and locking arrangement,
brake beams, hangers, and brake
blocks shall be secured as prescribed.
All brake gear pins (should be
chromium plated) shall be secured
with washers and split cotters.
iii) Vacuum gauges shall be properly
tested and adjusted using master
gauges before being fitted.
The vacuum brake is a braking system employed on trains and introduced
in the mid-1860s. A variant, the automatic vacuum brake system, became
almost universal in British train equipment and in those countries influenced
by British practice. Vacuum brakes also enjoyed a brief period of adoption
in the USA, primarily on narrow gauge railroads. However, its limitations
caused it to be progressively superseded by compressed air systems starting
in the United Kingdom from the 1970s onward. The vacuum brake system is
now obsolete; it is not in large-scale usage anywhere in the world,
supplanted in the main by air brakes.
Moving train contains energy, known as kinetic energy, which
needs to be removed from the train in order to cause it to stop. The
simplest way of doing this is to convert the energy into heat.
The conversion is usually done by applying a contact material to
the rotating wheels or to discs attached to the axles. The material creates
friction and converts the kinetic energy into heat. The wheels slow down
and eventually the train stops. The material used for braking is normally in
the form of a block or pad.Vacuum brakes were a big step forward in train
safety.
Overview
In the earliest days of railways, trains were slowed or stopped by the
application of manually applied brakes on the locomotive and in brake
vehicles through the train, and later by steam power brakes on locomotives.
This was clearly unsatisfactory, but the technology of the time did not easily
offer an improvement. A chain braking system was developed, requiring a
chain to be coupled throughout the train, but it was impossible to arrange
equal braking effort down the length of the train.
A major advance was the adoption of a vacuum braking system
in which flexible pipes were connected between all the vehicles of the train,
and brakes on each vehicle could be controlled from the locomotive. The
earliest pattern was a simple vacuum brake, in which vacuum was created by
operation of a valve on the locomotive; the vacuum actuated brake pistons
on each vehicle, and the degree of braking could be increased or decreased
by the driver. Vacuum, rather than compressed air, was preferred because
steam locomotives can be fitted with ejectors, which are simple devices that
create vacuum without the use of moving parts.
However, the simple vacuum system had the major defect that
in the event of one of the hoses connecting the vehicles becoming displaced
(by the train accidentally dividing, or by careless coupling of the hoses, or
otherwise) the vacuum brake on the entire train was
How they work :
The brakes themselves are in the form of metal shoes which press against the
train's wheels creating friction which slows the train down.
On a train equipped with vacuum brakes, every wagon or coach is equipped
with at least one set of brakes. The default position of each brake shoe is on
and the brakes are spring-loaded so that without vacuum, there is pressure
applied. Behind each brake shoe is a vacuum cylinder which contains a
piston, which draws the brake shoe forwards or backwards, or into the on or
off positions.
An airtight pipe runs along the entire length of the train. The air is pumped
out of this pipe by a pump in the locomotive to form a vacuum. As a vacuum
forms in the vacuum cylinder behind the piston, the piston is pushed
backwards by atmospheric pressure, thereby drawing the brake shoe
backwards into the off position.
The brakes will automatically move forward to the default "on" position if
the vacuum is broken. The train driver can apply the brakes by opening a
valve which lets air into the pipe thus breaking the vacuum. If the train
breaks up or the pipe develops a leak, the vacuum will again be broken and
the brakes will come on.
The vacuum brake was considered preferential to the air brake in railroad
applications largely because it was cheaper to install on a steam locomotive.
Air brakes required a steam-powered compressor - bulky, noisy, unsightly
and using a lot of power, while the vacuum ejector used to generate vacuum
was a much simpler device, having no moving parts.
MAINTENANCE AT WORKSHOP:-
During POH all components of the brake
gear system shall be examined, repaired and
replaced as necessary. The pins and bushes
shall be examined for wear and replaced if
the radial clearance exceeds 0.75 mm.
Following items should receive particular
attention during POH:
i) Safety brackets provided for brake gear
components should be in accordance
with the approved drawings and shall
be examined for proper condition and
secured according to the prescribed
method.
ii) Vacuum cylinders and their trunnion
brackets, vacuum reservoirs and train
pipes, rubber hose & syphon pipes,
alarm chain apparatus including the
chain, disc and locking arrangement,
brake beams, hangers, and brake
blocks shall be secured as prescribed.
All brake gear pins (should be
chromium plated) shall be secured
with washers and split cotters.
iii) Vacuum gauges shall be properly
tested and adjusted using master
gauges before being fitted.