During normal driving, spring brakes are usually held back by which force?

During normal driving, spring brakes are usually held back by which force?

• A. Air pressure
• B. Hydraulic pressure
• C. Spring tension
• D. Vacuum

Answer: (A)

Air pressure keeps the spring brakes retracted during normal driving. Inside the spring brake chamber there are very strong springs that would apply the brakes if the air pressure were released. When you have adequate air pressure, it pushes a piston to compress and hold those springs in, keeping the brakes from engaging. If air pressure drops or is released, the springs push out and apply the brakes automatically. Hydraulic pressure or vacuum aren’t what holds the springs back in standard air-brake systems, and the springs themselves would cause braking if not countered by air pressure.

Air pressure keeps the spring brakes retracted during normal driving. Inside the spring brake chamber there are very strong springs that would apply the brakes if the air pressure were released. When you have adequate air pressure, it pushes a piston to compress and hold those springs in, keeping the brakes from engaging. If air pressure drops or is released, the springs push out and apply the brakes automatically. Hydraulic pressure or vacuum aren’t what holds the springs back in standard air-brake systems, and the springs themselves would cause braking if not countered by air pressure.