A rotary screw air compressor is a long-term asset, so the purchase decision should be driven by engineering numbers rather than brand claims. The right machine lowers energy cost, reduces downtime and keeps production running at full pressure. The wrong machine either wastes power through oversized capacity or stalls production because it is too small.
Start with flow and pressure
Work out the total compressed air demand of all equipment that can run at the same time, measured in cubic metres per minute (m³/min) or CFM. Add a 10–20% buffer for leaks and future growth. Then set the required working pressure. Most general plants run at 7–8 bar, while laser cutting, PET blowing and special processes need 10–40 bar.
- Total simultaneous demand, not the sum of nameplate ratings
- Working pressure required by the most demanding tool
- Growth reserve of 10–20%
Choose the drive type
Fixed-speed machines are cheaper to buy and suit plants with constant, near-full-load demand. Variable speed drive (VSD) compressors match output to fluctuating demand and typically save 15–35% of energy, which usually covers the price difference within two to three years.
Match the air quality class
Oil-injected machines are the standard choice for general manufacturing. Applications in food, beverage, pharmaceutical, electronics and semiconductor production require ISO 8573-1 Class 0 oil-free air, combined with dryers and filtration to reach the correct purity and dew point.
Think in total cost of ownership
Energy represents roughly 70–80% of a compressor lifetime cost. Compare specific power (kW per m³/min), service intervals, spare-parts availability and local after-sales support, not just the invoice price. A machine that is 2% more efficient can save more than its own price over a decade of operation.