| To release oil and water buildup | |
| To check for leaks | |
| So they can be inspected | |
| To verify they meet pressure requirements |
| Immediately fail | |
| Can still be used several times | |
| Can be used indefinitely | |
| Cannot be used |
| Trailer brakes | |
| Emergency and parking brakes | |
| Cab brakes | |
| Air brakes |