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oil-free screw
Oil-Free Air Compressors

Things to Consider When Purchasing a VSD Oil-Free Screw Compressor


You know that your application has an air demand that fluctuates, and you’ve already completed a full system audit that has determined your existing demand profile. But now you’re at a crossroads! You know that a Variable Speed Drive (VSD) compressor is best suited for processes with fluctuating demand, but you’re not sure which VSD compressor is the most ideal for your application’s specific needs. Here are five important elements that will help you decide:

  1. Turndown Evaluation. Understanding the demand profile is crucial here, given that some VSD compressors offer better turndown capabilities than others. Knowing the demand profile will let you specify a compressor that has the best performance across the required operating range.
  2. Avoid Speed Windows. Ensure that the compressor you select has been fully designed for Variable Speed Drive, rather than operating a compressor that has been programmed to operate within speed windows (or a compressor that’s programmed to operate within limited ranges).
  3. Avoid External Frequency Drives. If you choose to use an external frequency drive on compressors that haven’t been designed to operate at variable speeds, your compressor will not provide optimal turndown capability; speed windows will have the be programmed, or the compressor’s operating range will have to be limited.
  4. Compare SER Curves. Always evaluate Specific Energy Ratio (SER) curves for different compressor brands and models! You can do this by requesting a copy of the CAGI Performance Data Sheets that are available from each compressor manufacturer. One thing to keep in mind here is that 75% of a compressor’s lifecycle cost is through its power consumption – so choosing an energy-efficient model will result in returns through lower energy costs.
  5. Choose Purpose-Designed Machinery. Variable Speed Drive motors must be designed for inverter duty, have the necessary shielding to prevent pitting (which will then lead to premature bearings failures), and the necessary cooling capacity for slower-speeds operations – else, you risk compressor failure.

Understanding your air demand profile will help you choose the air compressor with the best fit, performance, efficiency and reliability for your individual application. If you need help with any of the above, reach out to Atlas Copco. Our compressed air experts are happy to assist!

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