| Show greater stopping power when lightly loaded | |
| Operate poorly when under load | |
| Show greater stopping power in bad weather | |
| Vary with |
| Deliver air from the air tanks to the air brakes | |
| Deliver air from the air compressor to the air tanks | |
| Allow water and oil to be expelled from air tanks | |
| Allow excess air pressure to be released from air tanks |
| Captures air that has been delivered to the brakes but was unused | |
| Delivers air from the air storage tanks to the brakes | |
| Delivers air from the air compressor to the brakes | |
| Ensures that the air storage tanks are properly pressurized |