Compressed air filters are used to remove water, oil, oil vapor, dirt, and other contaminants from a compressed air supply. In a standard compressed air filter the following components will be found between the point where the compressed air enters (the inlet) and the discharge port (outlet): a filter element, a filter bowl with a bowl barrier, and a drain. These components serve to draw contaminants from the flow and purge them from system.

Types of Compressed Air Filters

There are several types of compressed air filters.  Some examples include:

• Water separators
• Centrifugal separators
• Oil separators
• Air oil separators
• Demisters

Compressed Air Filter Technologies

There are several basic technologies used in compressed air filters. All are designed to remove contaminants, but some have specific features that make them better-suited for particular applications.

• General-purpose compressed air filters can remove liquid and solid contaminants of various sizes. They are designed for general industrial applications.
• Coalescing filters are used to remove oil and other contaminants at the sub-micron level. These filters are used in situations where general-purpose compressed air filters would leave too many contaminants in the system.
• Adsorbent oil vapor removal filters are designed to maintain a very pure airflow. They use adsorbent materials such as charcoal as a filter media to reduce vapor to less than 1 ppm. These devices are often used in conjunction with instrumentation, fiber optics and other components that are highly susceptible to damage and misreading due to contamination.
• Combination compressed air filters, which contain two or more of the above filter types. These inline compressed air filters are ideal for applications where the required air purity can vary depending upon the needs of the downstream devices.

Specifications

Filter size rating, maximum air volume, maximum inlet pressure, and operating temperature are the most important performance specifications to consider when selecting compressed air filters. As a rule, filter size rating is the low end of the size-range that is filtered or blocked.

Compressed air filters carry port specifications that indicate the thread type and measurement. Thread types include national pipe thread (NPT), British standard pipe thread, and metric pipe thread. There are many choices for NPT compressed air filters. Examples include:

• 10-32
• 1/8-in
• 1/4-in
• 3/8-in
• 1/2-in
• 3/4-in
• 1-in
• 1 1/2-in
• 2-in

In terms of features, some compressed air filters include a service life indicator, pressure gauge, or integral lubricator. Others are rated for caustic or corrosive media. Service life indicators may read the pressure drop across the compressed air filter, or use more advanced techniques. A pressure gauge for a compressed air filter provides a direct measurement of operating pressure or pressure drop.

Bowl size, bowl drain, and bowl material are also important parameters for compressed air filters. Bowls for a compressed air filter feature a manual or automatic drain and are made of materials such as:

• Aluminum
• Polycarbonate
• Steel
• Stainless steel
• Zinc

Standards

ISO 5782-1 - Pneumatic fluid power - compressed air filters - part 1

BS ISO 12500-1 - Filters for compressed air - test methods part 1

References

Image Credits:

Parker Hannifin Filtration and Separation Div. / Balston Products | Kaeser Compressors, Inc.