Before starting the braking system of the Indian railway we have to know about the Brake. now the question arises What is a Brake?
What is the brake?
A brake is a device by means of which artificial frictional resistance is applied to a moving machine member, in order to retard or stop the motion of a machine.
Two types of brake systems are used in Indian railway-
1.VACUUM BRAKE SYSTEM
2.AIR BRAKE SYSTEM
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1) VACUUM BRAKE SYSTEM
The vacuum brake is a braking system introduced in mid1860s, the automatic vacuum brake system, became almost universal in British train equipment and in countries influenced by British practice. Vacuum brakes also enjoyed a brief period of adoption in the United States, primarily on narrow gauge railroads. Its limitations caused it to be progressively superseded by compressed air systems starting in the United Kingdom from the 1970s onward.
PRINCIPLE OF VACUUM BRAKES-
The automatic vacuum brake consists of a continuous pipe—the train pipe—running throughout the length of the train. In normal running, a partial vacuum is maintained in the train pipe, and the brakes are released. When air is admitted to the train pipe, the air pressure acts against pistons in cylinders in each vehicle. A vacuum is sustained on the other face of the pistons so that a net force is applied. A mechanical linkage transmits this force to brake shoes which act on the treads of the wheels.
The fittings to achieve this are:
-> a train pipe: a steel pipe running the length of each vehicle, with flexible vacuum hoses at each end of the vehicles, and coupled between adjacent vehicles; at the end of the train, the final hose is seated on an air-tight plug;
:an ejector on the locomotive, to create a vacuum in the train pipe;
: controls for the driver to bring the ejector into action, and to admit air to the train pipe.
:a brake cylinder on each vehicle containing a piston, connected by rigging to the brake shoes on the vehicle; and:a vacuum (pressure) gauge on the locomotive to indicate to the driver the degree of vacuum in the train pipe
The brake cylinder is contained in a larger housing—this gives a reserve of vacuum as the piston operates. The piston in the brake cylinder has a flexible piston ring that allows air to pass from the upper part of the cylinder to the lower part if necessary.
The engine creates a vacuum which is transferred to the boogie by hosepipe, the proper vacuum is maintained throughout the system. if vacuum pressure exceeds the prescribed limits, the brakes are applied.
The driver can control the amount of braking effort by admitting more or less air to the train pipe.
1.the practical limit on the degree of vacuum attainable means that a very large brake piston and cylinder are required to generate the force necessary on the brake blocks.
2. for the same reason, on a very long train, a considerable volume of air has to be admitted to the train pipe to make a full brake application, and a considerable volume has to be exhausted to release the brake.
3. the existence of a vacuum in the train pipe can cause debris to be sucked in.
What is Air Brake System?
Brakes applied with the help of air are called Air Brakes and the system actuated to apply this phenomenon is known as Air Brake System.
An air brake is a conveyance braking system actuated by compressed air. Modern trains rely upon an air brake system that is based upon a design patented by George Westinghouse on March 5, 1872.
The Westinghouse system uses air pressure to charge air reservoirs (tanks) in each car. Full air pressure signals each car to release the brakes. A reduction or loss of air pressure signals each car to apply its brakes, using the compressed air in its reservoirs.
STRAIGHT AIR BRAKE SYSTEM-
In the air brake’s simplest form, called the straight air system, compressed air pushes on a piston in a cylinder. The piston is connected through mechanical linkage to brake shoes that can rub on the train wheels, using the resulting friction to slow the train. The mechanical linkage can become quite elaborate, as it evenly distributes force from one pressurized air cylinder to 8 or 12 wheels. The pressurized air comes from an air compressor in the locomotive and is sent from car to car by a train line made up of pipes beneath each car and hoses between cars. The principal problem with the straight air braking system is that any separation between hoses and pipes causes loss of air pressure and hence the loss of the force applying the brakes.
Twin-pipe air brake-
A solution to loss of brake pressure is the two-pipe system.In addition to the traditional brake pipe, this enhancement adds the main reservoir pipe, which is continuously charged with air directly from the locomotive’s main reservoir. The main reservoir is where the locomotive’s air compressor output is stored, and is ultimately the source of compressed air for all systems that use it.
Since the main reservoir pipe is kept constantly pressurized by the locomotive, the car reservoirs can be charged independently of the brake pipe.This arrangement helps to reduce
LIMITATIONS : –
1. If the brake pipe pressure is too low due to an excessive no. of brake applications, an emergency application will not produce a large enough volume of air flow to trip the triple valves, leaving the engineer with no means to stop the train.
2. Two pipe system is better than single pipe air brake system because this additional enhancement adds the main reservoir pipe, which is continuously charged with air directly from the locomotive’s main reservoir. This arrangement help to reduce the pressure loss problems and also reduces the time required for the brakes to release, since the brake pipe only has to recharge itself.