What was the air brake used for?

Question

anonymous · Answer

It's a clever safety system for railcars and tractor-trailer trucks.  The deal is that the brakes are forces against the wheel by a big spring, but kept away from the wheel by air pressure from a reservoir.  When you push the brake pedal, you open a valve that releases air pressure, and allows the brakes to be forced against the wheel by the springs.  When you let go, the valve closes an the pressure builds up, removing the brakes.

It's clever because it's failsafe.  If something happens to the air pressure system -- somethign breaks, a car couplign fails -- the brakes automatically apply and stop the car.

Mind you, I'm describing safety or parking brakes.  The brakes used for slowing and stopping normally often operate the other way, with air pressure pushing the brakes against the wheel.