Understanding air brakes: How they work in freight trains

Freight trains depend on air for their brake applications in two ways:

To signal the brake to apply or release the brakes by changes in the air pressure through a Brake Pipe that runs the length of the train.
To apply the air to the brake cylinder from a reservoir (called an auxiliary reservoir) on each wagon.

The key to this system is a set of valves on the wagons called a triple valve or control valve.

This set of valves has three functions:

To allow air to flow from the wagon's auxiliary reservoir to the brake cylinders when the brake pipe pressure drops.
To release air from the brake cylinder when the brake pipe pressure rises to its full pressure (500 kPa in Australia).
To recharge the wagon's reservoir after the brakes are released and the brake pipe pressure rises to 500 kPa.

How does the air brake system function?

When the pressure in the brake pipe drops, the reduced air pressure allows the application valve in the wagon's triple valve to open. This opens a port that allows air to flow to the brake cylinder, applying the brakes to the wheels.

When the air pressure in the brake pipe rises, the increase in pressure;

closes the application valve so no more air flows to the brake cylinders,
opens a release valve that releases the air from the brake cylinders, and
opens a charging valve that allows air to flow from the brake pipe into the auxiliary reservoir, readying it for the next brake application.

The nature of the system means the reservoirs cannot be recharged while a brake application is active, or the brake application decreased once applied. It must be fully released, the reservoirs recharged, then re-applied.

Enhancements: The relayed or twin pipe system

To overcome some of the problems, a second pipe is often fed along the wagon from the main locomotive reservoirs at a pressure of around 800 kPa. This continually charges a second supplementary reservoir on the wagons.

This is called a relayed or two-pipe system.

While effective, this complicates brake activation. The triple valve and brake cylinders are set up for 500 kPa, and the triple valve still needs to control the brake applications.

A second relay valve is now needed to connect the higher-pressure supplementary air to the brake cylinders.

To achieve this, the triple valve feeds air to a dummy brake cylinder or dummy volume. This air pressure then activates the relay valve to open and allow air from the supplementary reservoir to the brake cylinders at the required pressure.

The ECP wagon system uses electronic and electric valves to control the wagons air brakes.

Understanding Electronic Control Pneumatic (ECP) brakes

In the ever-evolving world of freight transportation, safety and efficiency are paramount. Electronic Control Pneumatic (ECP) brakes combine the traditional power of pneumatic brakes with cutting-edge electronic control technology.

What Are ECP Brakes?

Traditionally, the brake pipe, responsible for running air pressure along the train, dictated how brakes were applied through a series of air valves. With ECP brakes, this signal is transformed from pneumatic to electronic. This means that the brakes can be activated more swiftly and uniformly across the entire train.

Advantages of ECP Brakes

1. Faster Response Time: One of the most significant advantages of ECP brakes is their rapid response. While traditional brakes can take up to 40 seconds to fully engage, ECP brakes can do so in around 6 seconds. This considerably shortens stopping distances, making trains much safer.

2. Synchronised Braking: With ECP technology, all cars in a train can brake nearly simultaneously. This ensures a more stable deceleration and reduces train buffing and noise.

3. Continuous Air Supply: The system keeps the brake pipe pressurised even when brakes are being applied. This consistent air supply helps maintain the functionality of the braking system and air reservoirs without the cost of a relay system for a separate reservoir-charging system.

4. Feedback Mechanism: ECP brakes provide real-time feedback on the status of the brakes and wagons, allowing for better monitoring and maintenance and a fail-safe braking system.

5. Cost Efficiency: Manufacturing and maintaining ECP components are less expensive compared to traditional systems, and their reliability with minimal moving parts further enhances their appeal.

How Do ECP Brakes Work?

ECP brakes operate using a cable that runs throughout the train, supplying 230 V DC power to each wagon. The locomotive houses an ECP control computer that generates powerline control signals along this cable in response to the driver's brake commands. These signals communicate with an electronic car control device (CCD) in each wagon, which then operates electrically controlled valves (AEM) to manage the application and release of air to the brake cylinders.

While ECP technology enhances the braking process, it still relies on an actual pneumatic brake application. An independent pneumatic emergency brake system is also in place, ensuring layers of safety

Conclusion

With the development of computer-controlled systems on locomotives in the past 20 years, the introduction of Electronic Control Pneumatic brakes marks a significant leap forward in freight transport technology. By enhancing safety, improving overall train control, and reducing costs compared to full pneumatic systems, ECP brakes offer tangible benefits to the industry.

FAQs

1. How do ECP brakes improve train safety?

ECP brakes provide faster, synchronised braking across all train cars, significantly reducing the stopping distance. It is also failsafe, programmed to apply the brakes if the train's safe operational brake limits are breached.

2. Are ECP brakes cost-effective?

Yes, ECP brakes are generally cheaper to manufacture and maintain than traditional systems, with high reliability reported across components

3. Do ECP brakes completely replace pneumatic systems?

No, while ECP brakes utilise electronic signals for application, the pneumatic mechanics remain unchanged for efficiency, with an additional emergency system in place.

3. Are there disadvantages with ECP braking?

The system is a higher-level technology than the more robust air brakes and requires more maintenance, specialised maintenance skills, and care.

A weakness in the system is the train line cable – kilometres of cable on a moving, vibrating train, exposed to extreme weather and pollutants, with multiple electronic connections and cable connections used by shunters and field staff. One small resistance or ground point can interfere with the communication frequency, causing the train to fail safe – known generally as cross-talk. This can cause disruption and delays in a busy system.

Some solutions to this have been implemented, but more can be done to improve ECP's reliability and functionality.

The train line with its plugs and connections is a vulnerable area. One poor connection can cause multiple train failures.

The ECP wagon's Car Control Device receives commands from the locomotive and controls the electric manifold.

How is a train rerailed?

There are three main methods used for re-railing locomotives and wagons.

Cranes
Ramps
Jacking sets

Cranes

In many rail organisations, cranes are now the go-to where possible. hey can be quick and easy to re-rail, and much of the risk of re-railing activities is given over to expert crane crews and riggers.

Cranes, however, have their drawbacks. They may not be readily available in county areas if overhead power lines are involved or the reach is too great across multiple rail lines; they may not be an option.

Ramps

Ramps are a quick and easy option but are limited by circumstances to their use. If the wheels are close to the track – no more than about 200mm, a locomotive is available to pull them on, and the rail is intact, they may be the best option.

A set of ramps is set in front of the derailed wheels as closely as possible. These are secured to the rail by nip chains and a ballast or dirt ram created to help run the wheel onto the ramp.

The vehicle is then run onto the ramps, re-railing it. Ramps can be used to re-rail multiple wheels at a time.

Jacking sets

These are designed to re-rail vehicles. How they are applied will depend on the type of vehicle.

They consist of a set of heavy-duty jacks and a traversing rail. A jack-controlling stand and a generator to provide hydraulic oil pressure.

The vehicle must be leveled and raised so the wheels are just above the rail height. This should be done with two jacks set under designed jacking points on the vehicle.

A traversing rail is then placed under the coupler, and a jack is set up under the coupler or, in some cases, on each side of the vehicle depending on the vehicle's design.

The vehicle is then supported by a jack sitting on a trolley on the top of the traversing rail. A second traversing jack sits on the rail to push the trolley across to re-rail the vehicle.

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