• Skip to primary navigation
  • Skip to main content
  • Skip to primary sidebar
  • Skip to footer

Sealing & Contamination Control Tips

Fluid Power Sealing and Contamination Control Information and Resources

  • News
  • Contamination Control
  • Filtration
  • Seals
  • Fluids
  • Design Guides
  • Advertise
  • Subscribe
You are here: Home / Blogs / The Goldilocks Principle of compressed-air cleanliness

The Goldilocks Principle of compressed-air cleanliness

July 29, 2016 By Ken Korane Leave a Comment

Share

Most anyone designing, using and maintaining a pneumatic system recognizes that proper filtration is necessary to keep equipment running at peak performance. The question is, what degree of filtration of necessary for a given system? Applying the Goldilocks principle, specifying filters that are too coarse can permit harmful contamination to pass through a filter and damage downstream components. But too fine of filtration and the system creates unnecessary pressure drop at the filter that wastes energy. To get compressed-air cleanliness that’s “just right,” a good guideline is ISO Standard 8573 that defines the quality of compressed air.

Part 1 of the standard specifies purity classes for compressed air and how they relate to certain contaminants. Parts 2 through 9 specify test
methods unnamed-1
for measuring levels of solids, oil aerosols, liquid water, oil vapor, solvents, biological contaminants and other substances in the compressed-air stream.

The standard specifically classifies three types of contaminants in compressed air: solid particles, water and oil. The tables shown below explain how they’re broken into specific classes for each type. Note that the size of solid particles is defined as the greatest length between two ends of a particle. The concentration of total oil includes liquids, vapor and aerosols. And for all
three types of contaminant,
Class 0 is defined as being more stringent than Class 1, and is specified by the equipment user or supplier


In practice, air cleanliness is expressed as a three-digit purity level for particles, water and oil.For example, air containing less than 10,000 particles sized between 1 and 5 µm, with a pressure dewpoint below 7° C, and containing less than 1 mg per cubic meter of oil would be considered
unnamedhaving an ISO 8573 Class 4:5:3 purity level.


Users should understand that the classification system is intended to provide a guide to different levels of air purity in compressed-air systems, not how air is filtered and treated. Nor does it define the purity levels needed for specific components or equipment.

That said, the standard does note that pneumatic-powered compon
ents, tools and machines have traditionally been supplied with air filtered by general-purpose filters with nominal particle-capture ratings of 40 or 5 microns. The purity levels they attain would be considered Class 7 and 6, respectively. These ratings are not absolute particle-removal ratings, according to the standard; air delivered by such filters remove at least 95% of the particles of a given rated size. Such filters give satisfactory service while minimizing pressure drop and power losses.

In most industrial settings, compressed air is used to power or pilot devices su
ch as valves, cylinders, grippers and motors. In these applications, the goal behind contamination control is to attain a compressed-air purity level that protects components from corrosion and excessive wear. Here, Class 7:4:4 air is likely suitable, and can be produced using a general-purpose, 40-micron particle filter and a refrigeration dryer with an oil trap.unnamed-2

On the other hand, compressed air that comes into direct contact with foods like beverages, meat and vegetables usually requires higher purity levels, perhaps Class 1:4:1 for solids, water and oil. The specific degree of compressed-air purity in such applications is left to equipment manufacturers, regulatory bodies and relevant industry associations—such as those governing food processing or pharmaceutical manufacturing. Seek assistance from qualified application engineers for help with specific filtration and treatment options.

Atlas Corpo oil-free compressors generate class 0 air.
Atlas Copco oil-free compressors generate class 0 air.

Filed Under: Blogs

Reader Interactions

Leave a Reply Cancel reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Primary Sidebar

Fluid Power World Digital Editions

Fluid Power World Digital Edition

Browse the most current issue of Fluid Power World and back issues in an easy to use high quality format. Bookmark, share and interact with the leading design engineering magazine today.

Fluid Power Design Guides

fluid
“sact
EXPAND YOUR KNOWLEDGE AND STAY CONNECTED
Get the latest info on technologies, tools and strategies for Fluid Power Professionals.

Footer

Sealing and Contamination Tips

Fluid Power World Digital Network

  • Fluid Power World
  • Mobile Hydraulic Tips
  • Pneumatic Tips
  • Hose Assembly Tips
  • Leadership in Engineering

Sealing & Contamination Control

  • Subscribe to Fluid Power World
  • Videos
  • Advertise with us
  • About us

Copyright © 2025 · WTWH Media, LLC · Privacy Policy