BID/Bidadi

BP: Brake Pipe
FP: Feed Pipe
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This article provides a knowledge regarding railway air brake system. Brake System in automobiles and locomotives is very common. There are various types of braking systems. You can find a comparison of vacuum brake system and air brake system below. This entire article is written in reference to air brake system in indian railways.
In order to achieve safe driving and reliable braking system Indian Railways has introduced air brake system. It has replaced the vacuum brake system for its quite many drawbacks. The train needs to be stopped in proper place and time and the brakes that are used in doing so should be reliable. Furthermore,...
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we need to use a braking system which will not have to be replaced or repaired every so often. So these days air brake is almost universally used in Indian Railways as it satisfies all of these properties.
The main reservoir (MR) has a capacity of 2000 ltrs. Containing compressed air at 8-10 kg/cm2. The pressure in feed pipe (FP), auxiliary reservoir (AR, 100 ltrs), control reservoir (CR), distributor valve (DV), and brake pipe is kept at 5 kg/cm2.
Suppose initially the train is running and the brakes are needed to be applied. The driver puts the driver brake valve (DBV) in application position which causes some air to release into the atmosphere. This causes a drop of air pressure in a particular position of the DV. This in turn causes the CR to apply force on the diaphragm causing it to move and establish a connection between the AR and the BC.The air of the AR goes to BC via this connection and forces a piston to move forward, this motion of the piston is transmitted to brake shoes via a mechanism and the brake shoes rub against the wheel, causing them to stop.
When releasing the brake the driver just restores the DBV into the original position and thus stopping the air from leaking into the atmosphere. On doing this the pressure of all parts of the DV again becomes 5 kg/cm2. In this position the CR causes the aforementioned diaphragm return to its original position and thus disconnecting the AR and BC. During this situation a release spring, which was compressed when the brake was applied, tries to return to its original position as the extra pressure on it due to AR pressure is removed, and thus the extra air to be driven out of the BC. This air comes out through a particular chamber of the DV and goes into atmosphere. Thus the brakes are released.
The isolating cocks are used to isolate the corresponding system in case of any repairs ,etc . the pressure regulating valves are used to regulate the pressure .This is the pressure in the MR is 8-10 kg/cm2 but in AR is 5 kg/cm2 .to maintain this difference , the PRV is used . The non-return valve is used to prevent the back flow of air from AR to the MR via the feed pipe. The function of the feed pipe is to supply the air to AR from the MR and maintain it at a constant pressure of 5 kg/cm2, as some air is lost every time the brakes applied. When pressure of the MR drops below 8 kg/cm2, it is manually refilled by a pump.
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Pipeline:
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In air brake system two different pipes run along the length of a wagon or coach from one end toanother. These pipes are called air pipes. One is called feed pipe and the other is called brake pipe. These are seamless heavy duty steel pipes with bore 25 mm in coaches and 32 mm in wagons. The bore of air pipes of wagons are intentionally kept larger so as to build up adequate air pressure on long roads uniformly over full lengths and to ensure efficient braking force up to the last vehicle on train.
The air hose and angle cock connect the FP and BP of two successive compartments. When any of the compartments needs to be detached from the main train, the angle cock is closed which cuts off the air flow the MR and then the corresponding compartment is detached.
The entire pipeline contains some joints like the T-joints, the one at the angle cock and so on. The more the number of joints, the more is the chance of leakage of air. The allowed leakage of the air is 0.2kg/cm2 in one minute.
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Source: Abhishek Dey (Air Brake System of Railway / Diesel Locomotive)