The air brake system includes the following valves :
| • | The automatic control valves |
| • | The various safety valves |
Air valves are pneumatic controls that route compressed air through
hoses and lines to or from the air brake components. The valves control the
following:
| • | The service brake chambers |
| • | The spring brake chamber assemblies |
| • | The trailer service air lines |
All air valves have air passages and internal moving parts. As the internal
parts move, the valves direct the compressed air to the desired location.
Each valve has at least one supply port in order to allow air to enter the
valve, and one delivery port in order to allow air to exit the valve. Some
valves have a control port that allows an air pressure source to control
when air can flow through the valve. An exhaust port allows air to vent
to the atmosphere. Some valves have special function control ports such
as balance or reservoir ports. The use of these special ports will be discussed
on the valves that have them.
Air brake valves operate either manually or automatically. Manual valves
require the driver to move a knob, handle, or pedal in order to work the valve.
Automatic valves use control ports or internal regulating parts in order
to work.
