https://gbtruck.ca/heavy-truck-brake-systems/

GB Truck and Diesel

An air brake or, more formally, a compressed air brake system, is a type of friction brake for vehicles in which compressed air pressing on a piston is used to apply the pressure to the brake pad needed to stop the vehicle. Air brakes are used in large heavy vehicles, particularly those having multiple trailers which must be linked into the brake system, such as trucks, buses, trailers, and semi-trailers

https://gbtruck.ca/heavy-truck-brake-systems/