How to Work Wheel Slide Protection System?

Wheel-Rail Adhesion is the physical grip (friction) between the steel train wheel and the steel rail. Since steel-on-steel has a very low coefficient of friction, managing adhesion is critical for both accelerating (traction) and stopping (braking) without the wheels slipping or locking up.

The Physics of Steel on Steel

Unlike rubber tires on asphalt, steel wheels have a tiny contact patch (roughly the size of a coin). This requires precise management of friction.

Why Do Trains Use Sand? (Sanders)

When adhesion is lost (e.g., due to wet leaves or ice), the train’s computer activates Sanders.

• Mechanism: Compressed air shoots dry sand from a box directly in front of the wheels.
• Effect: The sand is crushed between the wheel and rail, instantly increasing the friction coefficient and allowing the train to grip the track for braking or acceleration.

Wheel Slide Protection (WSP)

Similar to ABS in cars, modern trains use [Internal Link: WSP] systems. If a sensor detects that an axle is rotating slower than the train’s speed (locking up), it momentarily releases the brake pressure on that specific axle to regain adhesion, preventing “wheel flats” (flat spots on the wheel).

FAQ: Frequently Asked Questions about Adhesion

Q: What happens if a train cannot grip the rail?
A: It results in “Wheel Slip” during acceleration (damaging the rail) or “Wheel Slide” during braking (extending stopping distance dangerously).

Q: Do all trains carry sand?
A: Yes, almost all locomotives, EMUs, and trams are equipped with sandboxes for emergency braking and low-adhesion conditions.