Why EN 15625 Changes European Rail Braking Safety

EN 15625 standardizes automatic load sensing devices for railway braking. These systems adjust brake force by vehicle weight, ensuring optimal safety and preventing wheel damage.

December 15, 2024 2:02 am

Understanding EN 15625: Automatic Variable Load Sensing Devices in Railway Braking

EN 15625 is a crucial European Standard within the railway sector that outlines the requirements for the design, performance, and testing of automatic variable load sensing devices. These devices are integral components of a railway vehicle’s braking system, designed to adjust the braking force in proportion to the vehicle’s current weight (tare vs. laden).

The primary function of these devices, often called “load weigh valves” or “load-proportional braking systems,” is to ensure optimal braking performance across all loading conditions. By doing so, they significantly enhance safety, prevent wheel damage, and improve the overall efficiency and predictability of train braking.

Core Principle: The Need for Proportional Braking

The braking force required to stop a railway vehicle is directly related to its mass. An empty freight wagon requires significantly less brake force than a fully laden one. Applying the same maximum brake force to an empty wagon would cause the wheels to lock up, leading to wheel flats (damage to the wheel tread) and a dangerous reduction in braking efficiency (skidding). Conversely, applying the braking force designed for an empty wagon to a fully loaded one would result in dangerously long stopping distances.

EN 15625 addresses this challenge by standardizing devices that automatically detect the vehicle’s load and modulate the brake cylinder pressure accordingly. This ensures that the braking effort is always optimized for the vehicle’s current mass, maintaining consistent deceleration rates and preventing wheel-slide events.

Key Technical Requirements of EN 15625

The standard sets forth stringent technical specifications that these devices must meet. These requirements cover functionality, reliability, and safety.

Sensing Mechanism: The device must accurately measure the vehicle’s load. This is typically achieved by sensing the deflection of the suspension system (leaf springs or air suspension) as the vehicle is loaded. The standard specifies the required accuracy and range for this measurement.
Brake Force Adjustment: The device must translate the measured load into a proportional pneumatic output signal. This signal controls the main distributor valve, which in turn regulates the pressure supplied to the brake cylinders. The relationship between load and brake pressure must follow a specific, pre-defined curve.
Response Time: The device must react quickly to changes in load to ensure the braking system is always set correctly. EN 15625 defines maximum allowable times for the system to adjust following a change in load.
Fail-Safe Design: Safety is paramount. In the event of a failure of the load sensing device or its connection, the system must default to a safe state. This typically means defaulting to the “fully laden” braking condition, ensuring maximum brake force is available to prevent under-braking, which is considered more dangerous than a potential over-braking of an empty vehicle.
Environmental Resilience: Railway equipment operates in harsh environments. The standard requires devices to be tested for resistance to vibration, shock, extreme temperatures (-40°C to +70°C), humidity, and corrosion.
Type and Routine Testing: EN 15625 mandates a comprehensive testing regime, including laboratory type tests to validate the design and performance, as well as routine tests to ensure continued functionality throughout the vehicle’s service life.

Types of Automatic Variable Load Sensing Devices

While the goal is the same, the mechanical implementation of these devices can vary. The standard is performance-based, allowing for different designs as long as they meet the specified requirements.

System Type	Operating Principle	Advantages	Disadvantages
Mechanical Systems	A system of levers and linkages physically connects the vehicle’s bogie or axle box to the weigh valve. The vertical deflection of the suspension moves the lever, which adjusts the valve’s pneumatic output.	Simple, robust, reliable, and relatively low-maintenance. Widely used on freight wagons.	Can be less precise than pneumatic systems; susceptible to wear in linkage components over time.
Pneumatic Systems	Utilizes the pressure within the vehicle’s air suspension bellows as a direct indicator of the load. This pressure is fed to a relay valve that modulates the brake cylinder pressure accordingly.	Highly accurate, continuous adjustment, and integrates well with modern air-suspended vehicles like passenger coaches and multiple units.	Requires an air suspension system to be present; more complex than mechanical systems.
Hydro-Pneumatic Systems	A hybrid system that uses a sealed hydraulic sensor on the suspension to measure deflection, which in turn creates a pressure signal that controls the pneumatic weigh valve.	Offers high accuracy and can be retrofitted to vehicles without air suspension.	Adds hydraulic components, increasing maintenance complexity.

Integration and Importance in Modern Braking Systems

The automatic variable load sensing device is not a standalone component; it is a critical part of the vehicle’s overall pneumatic braking architecture. It works in close conjunction with the distributor valve, brake cylinders, and often the Wheel Slide Protection (WSP) system. A correctly functioning load sensing device makes the WSP’s job easier by providing a baseline brake pressure that is already appropriate for the load, reducing the likelihood of incipient wheel lock-up.

Compliance with EN 15625 is essential for manufacturers seeking to achieve interoperability and certification for their rolling stock across European networks. The standard ensures a predictable, safe, and efficient level of braking performance, which is fundamental to the integrity of modern railway operations.

Frequently Asked Questions (FAQ) about EN 15625

What is the primary purpose of EN 15625?

The primary purpose of EN 15625 is to standardize the requirements for automatic devices that adjust a railway vehicle’s braking force according to its load. This ensures consistent stopping distances and prevents wheel damage, whether the vehicle is empty or fully loaded.

Why is adjusting brake force based on load so important in railways?

Adjusting brake force is critical for safety and efficiency. Applying a “fully loaded” brake force to an empty vehicle can cause the wheels to lock and slide, damaging the wheels and increasing the stopping distance. Conversely, applying an “empty” brake force to a loaded vehicle would result in insufficient braking power and dangerously long stopping distances.

What happens if a load sensing device fails?

According to EN 15625, these devices must have a fail-safe design. In case of a malfunction, the system must default to a pre-determined safe state, which is almost always the maximum brake force setting (the “fully laden” condition). This prevents a potentially catastrophic under-braking scenario.

Does EN 15625 apply to all types of railway vehicles?

The standard is primarily applicable to mainline freight and passenger vehicles equipped with pneumatic braking systems where the vehicle’s mass can vary significantly. While the principles apply broadly, specific applications for locomotives, multiple units, or specialized vehicles may be covered by other, more specific standards.