Air Brake System of a Railway or Diesel Locomotive

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, 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.

Pipeline

In air brake system two different pipes run along the length of a wagon or coach from one endtoanother. 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 astobuild up adequate air pressure on long roads uniformly over full lengths andtoensure efficient braking force uptothe last vehicle on train.

The air hose and angle cock connect the FP and BP of two successive compartments. When any of the compartments needstobe 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/cm2in one minute.

Dirt Collector

This component functions as a trap and storehouse for dirt, dust and moisture coming with air from the compressor and retains it from going ahead. This is why it has given the name of ‘Dirt Collector’. The schematic diagram of the Dirt Collector is given below.

Dirt Collector can be of two types

1. Two way Dirt Collector

2. Three way Dirt Collector

The former is fitted between coaches between BP and FP, while the latter is used in wagons only. The air that passes the dirt collector is cleaned so that may not damage the dv. The air that enters the inlet port of the Dirt Collector, strikes against the centrifugal actions and passes through the outlet port to the check valve which chock ahead. Thus by this action dirt, dust and moisture get separated and collected in the chamber. Once it is stored here, it cannot mingle with the main stream of the air due to the presence of the non-return valve (NRV). The dirt is cleaned from the chamber during overhauling.

Image of Angle Clock for Railway

Common Pipe Bracket

One bracket has been hung from the under frame of the vehicle. It has been given the name of “Common Pipe Bracket”. On this bracket DV and the CR supplied by any manufacture can easily be fitted. This bracket facilities easy removal and fitment of DV and CR in case either one gets damaged.

There is no necessity of opening other connections for their removal. This bracket has been provided air passage connection for AR, CR, BP and BC independently. The end of the passages have been provided with flanges housing necessary rubber seals, so as to make fully leak-proof so that the air in one passage doesn’t find its way to another passage. The common pipe bracket has been provided 5 passages – right side 3 and left side 2 connected to main pipe dirt collector,2 ARs and 2 BCs. This bracket also purifies the air once again.

Control Reservoir

Control Reservoir has been provided to control the air pressure when the DV has activated at its brake applications and release. Capacity of CRS for coaches is 9 liters and it requires the pressure of 5 kg/cm2.CR is like small ball with one side opened and has been provided with drain plug for cleaning the reservoir dust and water in sick lines if necessary .It is fitted to the common pipe bracket’s back side with 4 studs and nuts along with rubber seal for keeping it air tight.

Image of brake Cylinder

AuxillaryResrvoir

It has been provided in the air brake system to feed compressed air to the brake cylinder through DV at the time of brake application. One AR is provided each in freight stock vehicles and two ARs are provided in all coaching stock vehicles.

The AIR has been provided with two holes on either end for charging air pressure .One end is connected with check valve with choke or non-return valve and the other end is connected to DV. On coaches two ARs of 100 liters or one AR of 200 liters is provided and also has been provided with a drain hole at the bottom which is plugged by means of a drain plug of diameter of 19 mm with sealing washer and the joint is made air tight. The drain hole has been provided in order to drain out water accumulated in AR due to moisture in air.

COMPARISON OF VACCUM BRAKES AND AIR BRAKES

AIR BRAKES / VACUUM BRAKES
Brake pipe and feed pipe (twin pipe system for coaching stock, single pipe system for goods stock). / train pipe – single pipe
Passenger Emergency Alarm Signal Device / Alarm Chain Apparatus
Passenger emergency valve / Clappet valve
Hose coupling for brake pipe and feed pipe / Hose coupling for train pipe
Auxiliary reservoir 100lts capacity / Vacuum reservoir 320lts capacity
Works on the compressed air i.e. the compressed air pushes the piston of the brake cylinder / Works on vacuum i.e. some air is introduced in the vacuum which is used to apply the brakes