Single Pipe Braking System

About Single Pipe Braking System:

Air brake system is most efficient and reliable braking system used to run heavy and long trains at high speeds. It has following advantages:-

• Short braking distance.
• Higher braking force.
• Reduced brake power deterioration.
• Uniform brake power over train length.
• Compact and light equipment.

Air brake system is classified as:

• Single pipe air brake system
• Twin pipe air brake system
• Air brake system used in freight stock is single pipe graduated release air brake system.

 

Principle Of Operation:

Air Brake Freight stock is fitted with single pipe graduated release air brake system. In the single pipe, brake pipes (BP) of all wagons are connected.

Also, all the cut off angle cocks is kept open except the front cut off angle cocks of BP of leading loco and rear end cut off angle cock of BP of the last vehicle. Isolating cock on all wagons is also kept in open condition. The auxiliary reservoir is charged through distributor valve at 5kg/cm2.

 

Charging Stage:

During this stage, brake pipe is charged to 5 kg/cm2 pressure which in turn charges control reservoir and auxiliary reservoir to 5 kg/cm2 pressure via distributor valve. At this stage, brake cylinder gets vented to atmosphere through the passage in Distributor valve.

 

Application Stage

For the application of brakes, the pressure in brake pipe has to be dropped. This is done by venting air from driver‟s brake valve. Reduction in brake pipe pressure positions the distributor valve in such a way that the control reservoir gets disconnected from brake pipe and auxiliary reservoir gets connected to the brake cylinder.

This results in the increase in air pressure in brake cylinder resulting in the application of brakes. The magnitude of the braking force is proportional to the reduction in brake pipe pressure.

 

Release Stage:

For releasing brakes, the brake pipe is again charged to 5 kg/cm2 pressure by the compressor through driver‟s brake valve. This action positions distributor valve in such an away that auxiliary reservoir gets isolated from brake cylinder and brake cylinder is vented to atmosphere through distributor valve and thus brakes are released.

Air Brake Sub Assemblies:

Distributor valve is the most important functional component of the air brake system and is also sometimes referred to as the heart of the air brake system. The function of the distributor valve is to distribute compressed air received from brake pipe to auxiliary reservoir and control reservoir.

In addition to this, it also senses drop and rise in brake pipe pressure for brake application and release respectively.It is connected to brake pipe through branch pipe. Various other components connected to the distributor valve are the auxiliary reservoir, brake cylinders, and control reservoir.

 

Brake Cylinder:

At the time of brake application, compressed air from Auxiliary Reservoir, via Distributor Valve, enters Brake Cylinder and moves its piston outwards. The force on the piston in the Brake Cylinder is multiplied and transmitted to Brake via the brake rigging.

 

Auxiliary Reservoir:

The auxiliary reservoir stores air required to fill the Brake Cylinder for brake application. In Single Pipe System, it receives the supply of compressed air from Brake Pipe through Distributor valve at 5.0 kg/cm2.

 

Cut Off Angle Cock:

• Angle Cock is provided on the brake pipe at either end of each wagon which is used for opening or closing the Brake Pipe.
• When Angle Cocks are closed, the connected Hoses get vented and, then, they can be uncoupled without any danger without any danger.
• When the handle of Cut Off angle Cock is parallel to the pipe, it is open and when at the right angle to the pipe, it is closed.

 

Hose Coupling:

Hose Coupling is provided to connect Brake pipe hoses of consecutive wagons. The brake pipe is thereby made continuous throughout the train. It enables the supply of compressed air to all wagons for activating their brake equipment.

 

Dirt Collector:

The Dirt Collector is provided at the junction of Brake pipe and Branch pipe. It removes dust from the compressed air coming through the brake pipe so that only dust free air enters the Distributor valve and Auxiliary Reservoir.

 

Guard’s Emergency Brake Valve:

The Valve is provided in the rake Van for use by the Guard for application of brakes from the Brake Van during the emergency.

 

Pressure Gauge:

The gauge is provided in Brake Van to enable the Guard to check the pressure in the Brake Pipe.

 

Quick Coupling:

The function of Quick Coupling is to fix the pressure gauge in BP pipe provided in Brake Van. Guard has to fix the BP pressure gauge by press fit into the quick coupling.

 

Slack Adjuster:

Slack adjuster (also known as brake regulator) is a device provided in the brake rigging for automatic adjustment of clearance/slack between brake blocks and wheel. It is fitted into the brake rigging as a part of mechanical pull rod. The slack adjuster is double acting and rapid working i.e. it quickly adjusts too large or too small clearance to a predetermined value known as A dimension.

Duties of Drivers And Guards Of Air Braked Goods Trains:

During Originating Examination ensure that:

• Hand brakes of all wagons are fully released.
• Operating handle of empty load box is incorrect position i.e. in empty position when the wagon is empty or lightly loaded and in loaded position when the wagon is loaded beyond the specified value.
• Hose coupling of brake pipe on consecutive wagons are coupled to one another to form a continuous air passage from the locomotive to the rear end of the train.
• All the angle cocks, except that at the rear end of the train, are kept " OPEN".
• Hose coupling at the rear end of the train is placed on its hose coupling support.
• Isolating cocks of distributor valves of all wagons are in "OPEN" position.
• Isolating cocks of feed pipes (wherever existing) of all wagons are in" CLOSE" position.

After full charging of the system, brake pipe pressure should be as below:

 

 Piston strokes in empty & loaded condition are within the limits. The specified limits are:

• Empty wagons – 85 ± 10 mm
• Loaded wagons – 130 ± 10 mm
• Brake blocks of wagons are mating the wheels.
• Release the brake & ensure that
• The piston rod of brake cylinder is fully inside.
•  Brake blocks are away from the wheel treads.
•  Before starting the train carryout BRAKE CONTINUITY TEST as given at section 5.0 to ensure continuity of the brake pipe pressure throughout the train.
• Set the red needle in Air flow meter to the position of a white needle which is equivalent to leakage/charging rate of the brake system.

Stopping of the Train:

On level track:

When the train is to be brought to a stop on the level, first apply brakes with a small reduction of brake pipe pressure in the train pipe by auto brake valve (A-9). This will allow the rear portion to run smoothly. A heavier reduction of brake pipe pressure may then be made.

In order to make the final stop very smooth, the brake application should be gradually reduced by increasing the brake pipe pressure as the train is about to come to stop. The loco independent brakes should only be applied gradually when the speed has come down to about 5 kmph. This would help in bunching of the train and would help in the easier start.

 

On Down Grade:

Destroy brake pipe pressure partially on trains by automatic brake valve except in case of emergency stop. The application of air brakes being increased as the speed comes down. When speed comes down, if proportionate brakes are in operation, the train shall be brought to stop with train and loco air brakes on. The heavy application should never be made or the rear portion is liable to run in violently and damage to rolling stock may occur. Similarly, the quick release will cause the front portion to run out resulting in service jolts.

 

On Up Grade:

When a train is brought to stop on an upgradient, the brakes should be kept applied by the automatic brake valve, till the train actually stops. This will prevent the rear portion from rolling back.

 

Note: After stopping of train keep brakes on locomotive and train applied by A-9 brake valve. It will prevent rolling back of the train on gradients. Do not leave the train with only SA-9 in applied condition.

Starting of the train after stopping:

Do:

• Move the brake valve handle (A-9) to release position.
• Wait for 3 minutes to release the brakes for single pipe brake system. Earlier starting, if train brakes have not been released fully, may result in an excessive force on the coupler and brake binding.
• Ensure that air flow indicator white needle coincide with the fixed red needle and light & buzzer is not giving any indication.

Do not:

• Do not move the train unless air pressure is achieved 5Kg/cm2 in the loco BP gauge.