EN 15625: Standards for Railway Brake Control Valves

What is EN 15625?

EN 15625 is the European Standard titled “Railway applications – Braking – Control valves and self-venting accelerators.” It governs the “brain” of the Automatic Air Brake system: the distributor valve. This component is responsible for sensing pressure changes in the brake pipe and command the filling or venting of the brake cylinders.

Because international trains consist of wagons from many different owners, Interoperability depends on every control valve reacting with identical timing and sensitivity. EN 15625 ensures that a braking command initiated by the locomotive propagates through the entire train consistently, preventing dangerous longitudinal forces.

Functional Requirements

The standard specifies the precise Technical Delivery Conditions for the functional stages of the braking process:

• Application and Release Timing: Standardized “filling times” for the brake cylinder to ensure smooth deceleration.
• Sensitivity and Insensitivity: The valve must react to deliberate pressure drops (braking) but ignore small, accidental fluctuations (insensitivity) to prevent “ghost braking.”
• Graduable Application: The ability to increase or decrease braking force in small, precise steps.
• Automatic Operation: The requirement that the brakes apply automatically if the brake pipe pressure drops to zero (e.g., in the event of a train parting).

Testing and Validation

To comply with TSI LOC&PAS and freight standards, control valves must undergo rigorous testing:

• Climatic Testing: Ensuring the rubber diaphragms and seals function in temperatures from -40°C to +70°C.
• Endurance Testing: Subjecting the valve to tens of thousands of cycles to simulate years of Rolling Stock Maintenance intervals without failure.
• Vibrational Resistance: Testing the valve’s ability to maintain its settings while subjected to the constant mechanical shocks of the track.

Self-Venting Accelerators

EN 15625 also covers “accelerators.” On long trains, the air pressure signal moves slowly. Accelerators detect a braking command and locally vent air from the brake pipe, “speeding up” the signal transmission so that the rear wagons start braking nearly as fast as the front ones.

Comparison: Control Valve Performance Classes