Getting To Know Your Air System: Air Dryers

How Air Dryers Keep Your Air Line From Freezing Up

Semi-truck air dryers are one of the most important components in the vehicle's braking system. Without a properly working air dryer, your air line can freeze up, causing damage to your braking system. Every vehicle that has an air brake system uses an air dryer to remove particulates from the air produced by the compressor.

If you've ever wanted to know a little more about the commercial air dryer in your air system, you've come to the right place. To help grow your knowledge base on air dryers, our experts have written the following article. Read on to learn more about heavy-duty air dryers!

What is a Semi-Truck Air Dryer?

Commercial truck air dryers use a desiccant filtration system to remove oil and water from compressed air. Air dryers are developed to remove most liquid and water vapor from the compressor's discharged air on its way to the air brake reservoirs. The resulting air is clean and dry as it is pushed into the braking system, helping to avoid air-line freeze-ups.

What is an Air Dryer Desiccant Filter?

A desiccant filter is made with a special adsorbent material adept at absorbing water. With layered desiccant filter elements, air dryers are designed to eliminate particulate while the beads inside strip moisture from the compressed air. Desiccant beads will also attract moisture from the equipment reservoir, which actively dries the equipment. This specially designed material features hygroscopic properties, allowing the air dryer to maintain a dry environment by pulling and holding water molecules within itself.

How Does an Air Dryer Work?

Air compressors are designed to ensure the air tanks are full, which means that there is always air available. Air has a level of humidity that contains water vapor whether in dry or damp climates. As air is compressed it becomes heated, cooling down as it moves from the discharge line to the air tank. When the compressed air cools, the resulting condensation makes pools of water in the air tanks. In the water, oil from the compressor and any contaminants that got through the compressor's air filter will be present.

Contaminants then enter the supply port through the air dryer's end cover. While the compressed air travels into the end cover assembly, the flow changes several times. This charging process condenses contaminants which then drop to the bottom of the air dryer end cover.

Next in the process, compressed air leaves the end cover moving into the desiccant cartridge. Inside the cartridge, compressed air flows through an oil separator designed to remove water, oil, and any additional solid contaminants. After the air exits the oil separator, the next area is the desiccant drying column. The air is moist as it flows through the column of desiccant material, becoming progressively more dry as the water vapor is collected.

How Does an Air Dryer Purge Cycle Work?

The purge cycle of the air dryer begins when the governor causes the compressor to halt the air compression process. When the compressor unloads, the line that connects the governor unloader port to your vehicle's air dryer end cover control pressurizes. The purge valve opens when the air pressure is at capacity. Contaminants left inside the end cover sump are purged immediately when the valve opens. Simultaneously, the compressed air that was moving through the desiccant cartridge changes direction, flowing to the purge valve. This will remove all of the oil and solid contaminants that the oil separator collected.

The purge valve closes back up when the pressure in the air brake is reduced and the governor signals the compressor to start the process over again. This indicates the start of the next charge cycle.

Read More About Air Systems

If you are interested in learning more about the air system in your semi-truck, then you've come to the right place. To help you learn as much as possible, our expert team of trucking industry specialists have put together the list of articles below. Click on any of the links below to read more about air systems and the role they play in your semi-truck's overall health.

· Getting to Know Your Air System

· Getting to Know Your Air System: Air Tanks

· Getting to Know Your Air System: Air Compressors

· Getting To Know Your Air System: Gladhands

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