Major Parts Of The Air Brake System

1. Air compressor.

2. Reservoir (or air tank)

3. Unloader valve.

4. Brake valve

5. Brake chamber (or actuator)

6. Slack adjuster.

Unloader valve:

• The unloader valve helps to prevent the pressure of the air filling the reservoir from rising above a certain level.
• It is also known as the Governor. When the pressure exceeds a certain level, the unloader valve operates and expels excess pressure air.
• The unloader valve also blocks the flow of air (backflow) from the reservoir to the compressor when the air compressor is not running and the reservoir pressure is higher than the compressor's pressure.

Hence, Brake valve is not a part of the 'unloader valve' used in air brakes