Relate to the flow of air during a service brake application, which component is described as 'Auxiliary, brake cylinder'?

• A. Auxiliary brake cylinder
• B. Control valve
• C. Brake chamber
• D. Reservoir

Answer: (A)

When the service brake is applied, air pressure from the reservoir is directed by the service control valve to the brake actuators. The component described as “Auxiliary, brake cylinder” is the brake actuator itself—the device that uses that air pressure to create mechanical force. Inside this cylinder, the pressure moves a piston, which pushes on the push rod and ultimately causes the brake shoes or pads to press against the drum or rotor and slow the vehicle. In many diagrams this actuator is shown as a brake chamber, and the label “auxiliary” simply identifies it as the auxiliary circuit’s brake cylinder, the part that directly converts air pressure into braking action. The other parts—reservoir, control valve, and pipework—are responsible for supplying and directing that air, while the brake cylinder is the element that actually applies the brakes.