| To release oil and water buildup | |
| To verify they meet pressure requirements | |
| To check for leaks | |
| So they can be inspected |
| Can be used indefinitely | |
| Immediately fail | |
| Can still be used several times | |
| Cannot be used |
| Whenever you`re parked on a grade | |
| When air brake pressure is low | |
| Whenever you`re traveling down a grade | |
| Whenever you`re away from the vehicle |