Working of air brake

All vehicle brakes work the same way: the wheel is bolted to a metal piece, either a brake drum or a brake rotor. When you want to stop, friction devices are pressed against the metal piece. Their rubbing generates heat. The conversion of rotational force to heat causes the wheel to slow down, and eventually to stop.

On an air brake system, the shoes are moved with a device called an S-cam. It is connected to the brake chamber via the slack adjuster. In the brake chamber, there is always an operating rod (which moves the slack adjuster) and there's always a service brake chamber. It's just a bag that holds air. When you step on the brakes, air flows into the bag, which moves the operating rod.


On your drive and trailer axles, your brake chambers also contain your brake springs and the spring override chambers. The spring override chamber is another air bag. When the spring override chamber is empty, the spring pulls the operating rod, which puts the brakes on. When it's full, the spring is pushed back so your truck will move. The spring brake does two things. It's first your parking brake. It's pretty impressive--you can take a truck with 40,000 pounds of stuff in the trailer, stop it on a hill, set the spring brakes and expect the truck to remain there as long as you want. It's also your emergency brake--if you lose air pressure by accident, the spring brake will come on.