In an air brake system, which valve directs reservoir air into the brake chambers during braking?

• A. Brake valve
• B. Governor valve
• C. Safety valve
• D. Pressure relief valve

Answer: (A)

When braking, the key control is the valve that routes air from the reservoirs into the brake chambers. This brake valve opens a passage so the compressed air can flow to the brake actuators, pushing the pistons to apply the brakes. It also closes and vents air when you release the pedal, allowing the brakes to release again.

The governor valve, by contrast, manages the compressor’s operation: it senses system pressure and controls when the compressor starts and stops to keep the system within the desired range. The safety valve (pressure relief valve) protects the system from overpressure by venting air if pressure gets too high. The pressure relief valve serves as a safety device, not as the conduit that sends air to the brake chambers.

So the valve that directly directs reservoir air into the brake chambers during braking is the brake valve.