Truck air dryers collect and remove air system contaminants in solid, liquid, and vapor forms before they enter the brake system. They are designed to provide clean and dry air to the brake system components to help increase the system's life as well as reduce maintenance costs and eliminate the need for daily manual draining of the reservoirs.
The air dryer consists of a desiccant cartridge along with an aluminum end cover secured to a cylindrical steel outer shell. This end cover consists of a check valve, safety valve, three threaded air dryer connections, and a purge valve housing. The purge valve housing uses a purge valve mechanism and turbocharger cut-off feature designed to prevent loss of engine “turbo” boost pressure during a dryer purge cycle. To aid air dryer serviceability, the desiccant cartridge and discharge check valve assembly are screw-in types. The purge valve housing includes the heater and thermostat assembly and a discharge check valve. These two items are serviceable from the air dryer exterior. Servicing the screw-in desiccant cartridge will require that the air dryer be removed from the vehicle.
In linehaul applications, coalescing air dryer cartridges can last one to two years while non-coalescing cartridges can last two to three years. Other applications can shorten cartridge life. As a general rule, follow the manufacturer's recommended replacement intervals to get the best performance. In addition, replace the air dryer cartridge if you start seeing an increase in moisture in the wet tank.
Note that drivers and maintainers that see a sudden increase in moisture in the wet tank, or an increase in moisture short of the normal cartridge replacement time, often assume it’s a problem with the air dryer or cartridge. That may not be the case.
Dryers are designed to handle a certain amount of air. A misapplication of the vehicle that demands more air than the system was designed for, or a leak in the system, may cause air system demand that is higher than the dryer was designed for. The leak can be located and repaired, but a change in air demand may require an air system upgrade.
Some maintainers write the date on the air dryer cartridge when they install it, check the date during routine maintenance, and replace the cartridge when it reaches or approaches its expected lifecycle. Others track the cartridge's age on a maintenance log or simply replace it as part of every other preventive maintenance routine.
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