What is the main purpose of a brake pipe accelerator valve compliant with EN 15612?

The main purpose is to significantly speed up the propagation of the brake signal along a long train. When it detects a rapid drop in brake pipe pressure, it locally vents air to the atmosphere, causing a chain reaction that results in a faster, more uniform brake application across the entire train, thereby reducing stopping distances and dangerous in-train forces.

Why is EN 15612 so important for railway safety?

EN 15612 is crucial for safety because it standardizes the performance of a critical braking component. By ensuring accelerator valves work reliably and predictably, it directly contributes to shorter emergency stopping distances and prevents high longitudinal forces that can cause derailments, especially on long, heavy freight trains.

Does every railway vehicle need a brake pipe accelerator valve?

No, not every vehicle requires one. They are most beneficial and often mandated for long trains, particularly freight trains, where the time lag in the pneumatic brake signal is most pronounced. Shorter trains or passenger trains equipped with modern electro-pneumatic (EP) brakes may not need them as the brake signal is transmitted electrically and is virtually instantaneous.

What kind of tests are required for an EN 15612 certification?

A valve must pass two main categories of tests for EN 15612 certification. First are the extensive 'Type Tests' performed on a new design, which include functional tests under extreme temperatures, endurance cycling, and resistance to shock and vibration. Second are the 'Routine Tests' performed on every unit manufactured to ensure consistent quality, focusing on key parameters like activation sensitivity and leak-tightness.

Why EN 15612 Changes European Rail Safety

EN 15612 standardizes railway brake pipe accelerator valves. These critical components ensure faster, safer braking, reducing stopping distances and dangerous forces, vital for long trains.

December 15, 2024 2:02 am

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Understanding EN 15612: The Standard for Railway Brake Pipe Accelerator Valves

EN 15612 is a European technical standard that specifies the requirements for the design, performance, and testing of brake pipe accelerator valves used in the pneumatic braking systems of railway vehicles. Its primary purpose is to ensure that these critical safety components function reliably and uniformly, enhancing the braking efficiency and safety of trains, particularly long freight trains.

The standard is a key part of the framework ensuring interoperability across the European rail network. By defining a common set of functional and testing criteria, EN 15612 guarantees that accelerator valves from different manufacturers will behave predictably when integrated into a train consist, contributing to consistent and safe braking operations.

The Critical Role of a Brake Pipe Accelerator Valve in Pneumatic Braking

In a conventional pneumatic brake system, a brake application is initiated by the driver, who reduces the pressure in the brake pipe that runs the length of the train. This pressure drop propagates from the locomotive to the last vehicle, triggering the control valve (distributor) on each wagon to apply the brakes. On long trains, this propagation can be slow, causing a significant delay between the braking of the first and last wagons. This differential braking can lead to dangerous in-train forces (compression or “buffing”), potentially causing derailment.

A brake pipe accelerator valve is designed to overcome this problem. It is a pneumatic device that detects a rapid rate of pressure drop in the brake pipe (indicative of a service or emergency brake application). Upon detection, it creates a local, additional vent of brake pipe air to the atmosphere. This action rapidly accelerates the pressure drop further down the train pipe, causing the next control valve to react much faster. This creates a chain reaction, significantly increasing the brake signal propagation speed.

Key Benefits of Using Accelerator Valves

Reduced Stopping Distances: By applying brakes more simultaneously along the train, the overall stopping distance is significantly shortened, which is crucial in emergency situations.
Minimized In-Train Forces: Uniform braking reduces the high compressive forces that build up when the front of the train brakes much earlier than the rear, enhancing operational safety.
Improved Brake Response Time: The system reacts more quickly to the driver’s commands, leading to more precise train handling.
Enhanced Safety on Gradients: Consistent and rapid brake application provides better control when operating on steep downhill gradients.

Core Technical Requirements stipulated by EN 15612

EN 15612 outlines a comprehensive set of requirements that these devices must meet. These are broadly categorized into performance, design, and testing criteria.

Performance and Functional Requirements

This is the heart of the standard, defining how the valve must operate under various conditions:

Activation Sensitivity: The valve must activate only when the brake pipe pressure drops at a rate characteristic of a deliberate brake application. It must remain insensitive to slow pressure drops caused by normal system leakage.
Venting Capacity: The standard specifies the volume of air the valve must discharge and the time within which this must occur to effectively propagate the brake signal.
Closing Mechanism: Once the local brake pipe pressure has dropped to a certain level, the accelerator valve must close reliably to allow the brake cylinders to fill and the braking system to stabilize. It should not fully deplete the brake pipe.
Operating Range: The valve must function correctly across a specified range of operating pressures (e.g., typically around 5 bar for a fully charged brake pipe) and ambient temperatures (-25°C to +70°C, with special provisions for colder climates).
Reset Functionality: After a brake application and subsequent release (recharging of the brake pipe), the valve must reset itself and be ready for the next application without any manual intervention.

Design and Construction

The standard also provides guidelines for the physical construction of the valve to ensure its longevity and reliability in the harsh railway environment:

Materials: Materials used must be resistant to corrosion, oil, and ozone. They must be durable enough to withstand the operational lifespan of a railway vehicle.
Mechanical Strength: The device must be robust enough to withstand the high levels of shock and vibration experienced during normal train operations.
Sealing and Air-tightness: The valve must be perfectly sealed to prevent any unintended loss of air from the brake pipe when in its normal, inactive state.
Interfaces: The connections and mounting points must conform to established railway standards to ensure easy and correct installation on a vehicle’s underframe.

Comparison: Braking System Performance With and Without an Accelerator Valve

The following table illustrates the significant impact of an EN 15612 compliant brake pipe accelerator valve on a long train’s braking performance.

Characteristic	Conventional System (Without Accelerator Valve)	EN 15612 Compliant System (With Accelerator Valve)
Brake Signal Propagation Speed	Slow (approx. 150-250 m/s). The pressure drop travels sequentially from wagon to wagon.	Rapid (up to 280-290 m/s). Each valve boosts the signal, ensuring near-simultaneous application.
Braking Response Uniformity	Low. Significant delay between the first and last wagon braking, causing a “wave” effect.	High. All wagons begin braking within a much shorter time frame of each other.
In-Train Longitudinal Forces	High. Strong compressive (buffing) forces are generated, posing a risk of derailment or cargo damage.	Significantly Reduced. Uniform braking minimizes the forces between wagons, leading to a smoother stop.
Emergency Stopping Distance	Longer. The total braking force is applied gradually as the brake signal travels down the train.	Shorter. Full braking force is achieved much faster across the entire train, reducing the stopping distance.
Overall Safety & Stability	Adequate for shorter trains but poses risks for long, heavy consists.	Greatly enhanced, especially for long and heavy freight trains, improving stability and reducing accident risk.

Testing and Certification according to EN 15612

To ensure compliance, a brake pipe accelerator valve must undergo a rigorous series of tests defined by the standard. This process validates its performance, reliability, and durability.

Type Tests: An extensive one-off testing regime performed on a new design to validate all its functional and endurance characteristics. This includes performance tests at temperature extremes, vibration and shock tests, and endurance tests (a high number of operating cycles).
Routine Tests: Simpler tests performed on every single valve produced to ensure that manufacturing quality is consistent and each unit meets the key performance criteria, such as activation sensitivity and air-tightness.

Only after successfully passing these tests can a valve be certified as compliant with EN 15612, making it eligible for use in interoperable railway traffic across Europe.

Frequently Asked Questions (FAQ) about EN 15612

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