How do train air brakes work?
Freight trains depend on air for their brake applications in two ways:
To signal the brakes to apply or release by changing 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.
Because of the system's design, the reservoirs cannot be recharged while a brake application is active. The brakes must be fully released, the reservoirs recharged, and then they can be re-applied.
Enhancements: The relayed or twin pipe system
To overcome some of these problems, a second pipe is often fed along the wagon from the main locomotive reservoirs at around 800 kPa (average locomotive main reservoir pressure). This continually charges a second supplementary reservoir on the wagons.
This is called a relayed or two-pipe system.
While effective, this difference in pressure 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 flow to the brake cylinders at the required pressure.
How do Electronic Control Pneumatic (ECP) brakes work
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, which runs 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.
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 braking, 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.
How is a train re-railed?
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 ramp 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 heavy-duty jacks and a traversing rail. A jack-controlling stand and a generator provide hydraulic oil pressure.
The vehicle must be levelled and raised so the wheels are just above the rail height. Do this with two jacks set under the vehicle's designed jacking points.
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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