The Shock Absorbers: UIC 617-7 & Passenger Coach Buffer Arrangements

What is UIC 617-7?

UIC 617-7 is the International Union of Railways (UIC) leaflet titled “Passenger stock – Buffer arrangements.” It defines the fundamental dimensions, characteristics, and functional requirements for the buffers used on passenger coaches. Buffers are the large cylindrical devices mounted at each end of a coach that absorb compressive forces, preventing damage to the coach body and ensuring passenger safety during acceleration, braking, and shunting.

This standard is crucial for interoperability. It ensures that any passenger coach built to UIC standards can be coupled with any other UIC-compliant coach or locomotive and form a safe, stable train consist. While automatic couplers (UIC 520/566) are common on heavy freight, traditional passenger stock often relies on screw couplings combined with these buffer systems.

Key Dimensions and Specifications

UIC 617-7 sets precise rules for buffer heads, plungers, and springs to ensure they engage correctly and absorb energy effectively.

• Buffer Head Shape: Defines the shape and diameter of the buffer face that makes contact with the adjacent vehicle. The standard allows for round or rectangular heads, but the contact surface must be smooth and free of sharp edges.
• Buffer Stroke: Specifies the maximum distance the buffer can compress (e.g., 80 mm or 100 mm, depending on the buffer type and vehicle).
• Buffer Force: Crucially, it defines the static and dynamic force characteristics of the buffer springs. The force must increase progressively as the buffer is compressed, providing controlled deceleration. This works in conjunction with the Draft Gear (which handles pulling forces and impacts at the center coupling) and is often specified in relation to the 2000 kN static load requirement in UIC 566.

Types of Buffers Covered

The leaflet acknowledges different designs based on the spring mechanism:

1. Spring Buffers: Use helical steel springs (often multiple nested springs) to absorb energy. These are the most common type.
2. Friction Buffers: Utilize friction plates to dissipate energy. These were more common historically but are less prevalent now due to their less predictable performance.

Interoperability and International Traffic

For a train to cross international borders seamlessly (under RIV – Regulations concerning the International Carriage of Dangerous Goods by Rail), its buffers must conform to these UIC standards. This includes:

• Alignment: Buffers must be aligned longitudinally on both sides of the vehicle.
• Height: The distance from the top of the rail to the center of the buffer head must be within specified limits (typically around 1060 mm).
• Spacing: The distance between the centers of the two buffers on a single vehicle is also standardized.

Comparison: Buffers vs. Automatic Couplers

While both systems manage longitudinal forces, they operate differently and are suited to different applications.