Supply Line

Emergency and Service Line
Emergency (Red), Service (Blue), 7 Way Power Cable (Green)

Supply Line

A supply line, also known as the emergency air line, is a crucial component of the air brake system in combination vehicles, such as semi-trailers. It supplies air to a trailer’s air tanks and controls the emergency trailer brakes.

Functions

The supply line serves two primary functions:

  1. Supplies Air: Delivers compressed air from the tractor to the trailer’s air tanks, ensuring that there is sufficient air pressure for the braking system.
  2. Controls Emergency Brakes: Loss of air pressure in the emergency line causes the trailer emergency brakes to activate.

Identification

Supply lines are often coded with the color red (red hose, red couplers, or other parts) to keep from getting them mixed up with the blue service line.