What is the function of the air compressor governor (rregullatori i presionit / valvula e shkarkimit) in a commercial air brake system?

1. To lubricate the wheel hub bearings with fine oil mist
2. To automatically ignite the glow plugs during cold starts
3. To regulate air pressure by cutting out compressor pumping when maximum pressure is reached and cutting in when pressure drops
4. To spray alcohol directly into the engine cylinders