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Moisture in Your Air System

Moisture in Your Compressed Air System

Excess moisture in your air system can create issues for your air compressor system, as well as your equipment that utilize it.

What Causes Moisture?

Moisture is an inescapable byproduct of compressed air.  All air contains a particular amount of water vapor. The amount of water held by the air differs with temperature and pressure; the higher the temperature, the more water the air contains. (Exactly why humidity tends to be higher in the summer than in the winter.)

To pressurize air, an air compressor squeezes the air into a smaller volume … about 12 times normal atmospheric pressure. And since pressurized air is not able to hold as much water, as the pressure increases, water vapor condenses back into liquid form.

Effects of the Moisture

Excess moisture can cause numerous issues for your air compressor and its components. The most serious is corrosion. Corrosion is a chemical reaction between a metal, oxygen and water; this is why metal rusts when it comes in contact with water.

Moisture in your compressed air systems can result in other problems for your system, too. Excess water may cause water hammer events, which can damage equipment and piping, and can block control lines, which prevents instruments from reading and actuating properly. In cold temperatures, ice can form inside the system, clogging filters, blocking intake or drain valves, and even crack pipes and other system components.

Additionally, moisture in the air stream may hamper proper lubrication or result in corrosion of air tools; Rust particles that develop in the air supply lines can become mixed with the air stream and damage equipment or harm the production processes; and if you’re using compressed air to spray paint, water can cause unflattering visual and texture effects in the finish. Other applications where moisture in air compressors is a real nuisance include sand and other material blasting, pneumatic tools, CNC machining centers, robotics, air cylinders and valve operation.


While it’s impossible to prevent moisture from entering your air compressor, you can get rid of most of it

Draining the Air Receiver Tank – The first place that moisture condenses is in the air receiver tank. When compressed air emerges from the pump, it’s hot. This temporarily keeps the water in its vapor state. As it makes its way to the receiver tank, the air cools down, allowing excess water vapor to condense back into a liquid. Draining the tank can be accomplished simply with a manual drain valve… which should be done daily. Automatic timer-based and pneumatic drain valves eliminate the need to remember to drain the receiver tank.

Water Separator Filter – The next stage of moisture removal for your air compression system is mechanical separation. This is done with a water separator filter. Typically, a water separator filter will remove between 40 – 60% of the water from the air.

Refrigerated Air Dryers – If additional moisture removal is required, the next step is refrigerated air dryers. These dryers work by chilling the air … remember that colder air holds less moisture than warmer air. As the air cools, excess water vapor condenses back into liquid form. The liquid accumulates in a water trap and is eliminated through an automatic drain valve. The dry air is then reheated to room temperature prior to it reentering the production lines. Just be sure your compressed air dryer is properly sized.

Desiccant Air Dryers – Desiccant air dryers are utilized in systems that require ultra-dry air. These dryers use a chemical process to remove the water … most commonly an activated alumina or molecular sieve desiccants are used. During the process, the compressed air is passed through a tower containing the desiccant material using a blower. These dryers use more energy than other drying systems and also consume between 5-18% of the compressed air supply in their operation. But if ultra-dry air is needed, they are the most effective method available to remove moisture from your air compressor and compressed air supply.

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