How much air go to the brake chamber engauge them?

To engage the air brakes, a sufficient amount of air pressure needs to be applied to the brake chambers. In most commercial vehicles, this air pressure typically ranges from 60 to 100 pounds per square inch (PSI) when the parking brakes are engaged, and around 90 to 120 PSI for service brakes during vehicle operation.

When the brake pedal is depressed or the parking brake is engaged, compressed air from the vehicle's air supply is directed to the brake chambers. Inside the brake chamber, it exerts force on a diaphragm or piston, which in turn actuates the brake shoes or pads against the brake drum or rotor to slow down or stop the vehicle.