What is the main purpose of the EN 15355 standard?

The main purpose of EN 15355 is to specify the technical requirements, performance criteria, and testing methods for distributor valves and distributor-isolating devices in railway pneumatic brake systems. This ensures safety, reliability, and interoperability of braking across the European rail network.

What is a distributor valve in a train's braking system?

A distributor valve is a pneumatic device on each railway vehicle that controls the brakes for that specific vehicle. It interprets pressure changes in the train's main brake pipe, initiated by the driver, and accordingly directs compressed air to the brake cylinder to apply the brakes or vents it to release them.

Why are there different braking modes like 'G' (Goods) and 'P' (Passenger)?

Different train types have different dynamic characteristics. Passenger ('P') trains require fast-acting brakes for shorter stopping distances. Long, heavy freight ('G') trains require slower, more gradual brake application and release times to manage the immense in-train forces and prevent derailments caused by wagons bunching up or stretching out too quickly.

What does 'interoperability' mean in the context of EN 15355?

Interoperability means that railway vehicles from different manufacturers and countries can be coupled together in the same train and operate safely and seamlessly. EN 15355 ensures that the braking system of every vehicle will respond in a standardized and predictable way to the driver's commands, which is essential for safe cross-border rail traffic.

Why EN 15355 Is Key to European Rail Safety & Interoperability

Explore EN 15355, the standard defining railway pneumatic braking. It ensures distributor valves provide critical safety, interoperability, and reliable performance for trains across Europe.

December 15, 2024 2:02 am

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Understanding EN 15355: The Core of Railway Pneumatic Braking

EN 15355 is a European Standard that specifies the requirements for the design, performance, and testing of distributor valves and distributor-isolating devices used in the pneumatic braking systems of railway vehicles. This standard is fundamental to ensuring the safety, reliability, and interoperability of braking systems across the European rail network.

The distributor valve is often considered the “brain” of a conventional pneumatic brake system on a rail wagon or coach. Its primary function is to translate pressure changes in the continuous main brake pipe, controlled by the driver, into a corresponding application or release of the brakes on its specific vehicle.

Core Functions of a Distributor Valve under EN 15355

A distributor valve compliant with EN 15355 must perform several critical functions with high precision and reliability. These functions are the foundation of safe train operation.

Brake Control and Operation

Charging: When the train’s braking system is being prepared, the distributor valve allows compressed air from the main brake pipe to charge an auxiliary reservoir on the vehicle to a nominal pressure (typically 5 bar).
Application: When the driver initiates braking, the pressure in the main brake pipe is reduced. The distributor valve senses this pressure drop, isolates the auxiliary reservoir from the brake pipe, and directs compressed air from the auxiliary reservoir into the brake cylinder. This action forces the brake blocks or pads against the wheels, creating braking force.
Holding (Lap Position): If the brake pipe pressure is held steady after a partial reduction, the distributor valve must maintain the corresponding pressure in the brake cylinder, ensuring a constant braking force.
Release: To release the brakes, the driver increases the pressure in the main brake pipe. The distributor valve detects this pressure rise, vents the air from the brake cylinder to the atmosphere, and reconnects the brake pipe to the auxiliary reservoir to recharge it.

Key Performance Characteristics

Graduability: The braking must be proportional. A small reduction in brake pipe pressure should result in a low brake cylinder pressure, while a large reduction should result in a high (or maximum) brake cylinder pressure. This allows for smooth and controlled braking.
Sensitivity: The valve must be sensitive enough to react to small, intentional pressure drops for braking but insensitive to minor, unintentional pressure fluctuations that occur during normal operation.
Inexhaustibility: The valve must be designed to allow for repeated brake applications and releases without significantly depleting the braking capability, ensuring consistent performance.

Technical and Performance Requirements in EN 15355

EN 15355 outlines a comprehensive set of technical specifications and performance benchmarks that a distributor valve must meet to be certified for use. These are verified through rigorous type-testing procedures.

Functional and Timing Parameters

The standard defines specific timing requirements for different operating modes, typically designated as ‘G’ (Goods/Freight) and ‘P’ (Passenger). These modes ensure that braking action propagates along the train at an appropriate speed for different train compositions.

Parameter	Brake Mode ‘G’ (Goods)	Brake Mode ‘P’ (Passenger)	Technical Significance
Application Time (0 to 95% of max pressure)	18 s to 30 s	3 s to 5 s	Ensures a controlled, slower brake application on long freight trains to manage in-train forces, and a rapid response on passenger trains for shorter stopping distances.
Release Time (from max pressure to 0.4 bar)	45 s to 60 s	15 s to 20 s	Controls the speed at which brakes are released. Slower release on freight trains prevents coupler slack and surges, while faster release on passenger trains allows for quicker departure.
Sensitivity Threshold (Pressure Drop to Initiate Braking)	Typically a drop of 0.2 to 0.4 bar		Defines the minimum intentional brake pipe pressure reduction that will trigger a brake application, preventing activation from minor system leaks.
Emergency Application	Maximum brake cylinder pressure in the shortest possible time.		Ensures the fastest possible braking response when the brake pipe is rapidly vented in an emergency situation.

Design, Construction, and Environmental Resilience

Materials: Materials used must be resistant to corrosion, oil, and ozone, and must be capable of operating reliably across the specified temperature range.
Environmental Conditions: The device must function correctly within a demanding temperature range (e.g., -25°C to +70°C, with special provisions for lower temperatures like -40°C).
Vibration and Shock: The standard mandates that the valve withstands the levels of vibration and shock typically experienced in railway operation, as defined in EN 61373.

The Role of the Distributor-Isolating Device

The distributor-isolating device is a crucial manual interface. It is a handle or cock that allows maintenance staff or train crew to pneumatically isolate the distributor valve and brake cylinders of a single vehicle from the main brake pipe. This is essential in cases where a vehicle’s brake system has a defect. Isolating the defective brake prevents it from affecting the braking performance of the rest of the train, allowing the train to continue its journey to a maintenance facility, albeit with reduced overall braking capacity.

Importance of EN 15355 for the Rail Industry

Ensuring Interoperability and Safety

The primary driver for EN 15355 is interoperability. A train may be composed of wagons from multiple countries and operators. By ensuring all distributor valves conform to a single standard, train operators can be confident that the train will brake as a single, cohesive unit, regardless of the origin of its individual vehicles. This predictability is the cornerstone of railway safety, preventing dangerous in-train forces and ensuring calculated stopping distances are met.

Standardization for Manufacturing and Maintenance

For manufacturers, the standard provides a clear set of design and performance targets. For maintenance depots, it standardizes testing procedures and spare parts, simplifying logistics and ensuring that repaired or replaced components will function as required. The clear marking requirements mandated by the standard also ensure full traceability of the component throughout its lifecycle.

Conclusion

EN 15355 is more than just a technical document; it is a critical safety and interoperability enabler for the European railway sector. By defining the precise behaviour of the distributor valve—the heart of the pneumatic brake system—the standard ensures that trains can operate safely and efficiently across borders, forming a reliable and integrated transport network. Compliance is not optional; it is a fundamental requirement for any rolling stock intended for operation on the mainline network.

Frequently Asked Questions (FAQ) about EN 15355

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