Compressed Air Quality

As illustrated in the following table, a number of different air quality levels can be achieved  - Information by Domnick Hunter

• Industrial applications typically use one of the first three air quality levels, and an individual plant can have end-uses that require different levels of air quality. Note: Standards do not exist for every one of the quality levels listed in the table, and other levels of air quality, such as medical air, also exist. Care should be taken to when using these terms - actual specifications for air quality should always be given
• ISO 8573 provides detailed standards on air quality classes for various levels of particulate, moisture, and lubricant contaminants, as show in the table below

• The AIR quality level required is a function of the dryness and contaminant level required by the end-uses, and is accomplished with separating, filtering and drying equipment
• Compressed air contaminants that produce hamful effects may be solids, liquids, or vapors
• Contaminants can enter the system at the compressor intake, or be introduced into the air stream by the system itself
  • Water, dirt, lubricant, chemical vapors, and exhaust fumes can enter through the intake
  • Lubricant, metal particles, carbon, Teflon, rust, and pipe scale can be introduced by the system itself. Note: compressor lubricant and inline lubricators are not eth only source of hydrocarbons in a compressed air system and lubricant-free compressors do not eliminate the need for filtration

• The higher the quality, the more the air usually costs to produce. Higher quality air usually requires additional equipment, which not only increases initial capital investment, but also makes the overall system more expensive to operate in terms of energy consumption and maintenance costs.
• One of the main factors in determining air quality is whether or not lubricant-free air is required. Lubricant-free air can be produced with either lubricant-free compressors, or with lubricant-injected compressors and additional separation and filtration equipment
  • If only one end-use requires lubricant-free air, only the air supply to it should be treated to obtain the necessary quality, or it should be supplied by its own lubricant free compressor
  • Lubricant-free rotary screw and reciprocating compressors usually have higher first costs, lower efficiency, and higher maintenance costs than lubricant-injected compressors. However, the additional separation and filtration equipment required by lubricant-injected compressors will cause some reduction in efficiency, especially if systems are not properly maintained
  • Careful consideration should be given to the specific end-use for the lubricant-free air, including the risk and cost associated with product contamination, before selecting a lubricant-free or lubricant-injected compressor. Centrifugal compressors can be a good choice for applications requiring lubricant-free air