Air Brakes 101
- By Rachelle Biggs
- Published 11/9/2005
- Driving
- Unrated
The Air Compressor pumps air into the air tanks (also referred to as reservoirs), supplying the compressed air to power the air brake system and other air operated devices. (Windshield wiper, window) It is lubricated by engine oil or its own oil supply and is gear driven. A Safety Valve is usually installed in the reservoir closest to the compressor. Its function is to protect the system from over pressurization and will release air when pressure reaches approximately 150 psi.
The Air Compressor Governor controls when the air compressor will pump air into the reservoirs. When air tank pressure rises to the set maximum, or the “cut out” level, (around 125 psi) the governor stops the compressor from pumping air. When the tank pressure falls to the “cut in” pressure (around 100 psi), the governor allows the compressor to start pumping again.
An Air Dryer helps to keep the system free of contaminants. A filter, typically containing a desiccant, is installed between the compressor and service reservoir to remove moisture and oil from the air before it enters the reservoir.
An Alcohol Evaporator injects alcohol mist into the flow to reduce the risk of freeze-up. It is not normally used in a vehicle with an air dryer. Its purpose is to prevent moisture from freezing in the air system in cold temperatures.
Air Storage Tanks or Reservoirs store compressed air. The number and size of air tanks varies. The tanks will hold enough air to allow the brakes to be used several times even if the compressor stops working. The tractor’s supply air tank receives air from the compressor and delivers it to the primary and secondary air tanks in the tractor. Most trailers also have primary and secondary tanks. The reservoir closest to the compressor is commonly referred to as the “wet tank” because that is where most moisture condenses. Reservoirs are equipped with Drain Valves, either manually and/or automatically operated, so that water may be purged. Compressed air usually has some water and oil in it, which tends to collect in the bottom of the air tank. The water can freeze in cold weather and can lead to brake failure. The Air Supply Gauge (s) in the tractor show how much pressure is in the air tank.
The Air Compressor Governor controls when the air compressor will pump air into the reservoirs. When air tank pressure rises to the set maximum, or the “cut out” level, (around 125 psi) the governor stops the compressor from pumping air. When the tank pressure falls to the “cut in” pressure (around 100 psi), the governor allows the compressor to start pumping again.
An Air Dryer helps to keep the system free of contaminants. A filter, typically containing a desiccant, is installed between the compressor and service reservoir to remove moisture and oil from the air before it enters the reservoir.
Air Storage Tanks or Reservoirs store compressed air. The number and size of air tanks varies. The tanks will hold enough air to allow the brakes to be used several times even if the compressor stops working. The tractor’s supply air tank receives air from the compressor and delivers it to the primary and secondary air tanks in the tractor. Most trailers also have primary and secondary tanks. The reservoir closest to the compressor is commonly referred to as the “wet tank” because that is where most moisture condenses. Reservoirs are equipped with Drain Valves, either manually and/or automatically operated, so that water may be purged. Compressed air usually has some water and oil in it, which tends to collect in the bottom of the air tank. The water can freeze in cold weather and can lead to brake failure. The Air Supply Gauge (s) in the tractor show how much pressure is in the air tank.