What CFM actually tells you

CFM is a volumetric flow rate: the volume of air delivered per minute. Compressor data may be stated as FAD (free air delivery), inlet CFM or displacement. For purchasing decisions, compare delivered flow at the required working pressure. Never compare one supplier’s displacement figure with another supplier’s FAD.

Pressure and flow must be specified together. A machine needing 20 CFM at 7 bar(g) cannot be evaluated from motor horsepower alone. Two compressors with the same motor rating can deliver different flows because of pressure, air-end design and control strategy.

Build an air-demand inventory

Walk the plant and record every pneumatic cylinder, tool, blow gun, packaging machine, CNC accessory and process nozzle. Use the equipment manual or a measured value at normal operation. Record operating pressure, rated flow, minutes used per cycle, cycles per hour and whether it runs with other equipment.

Use the example only as a worksheet pattern; actual demand must come from your equipment and production cycle.

Apply duty and simultaneity correctly

For each user, estimate average demand as rated flow × duty factor. Then build a peak scenario for equipment that can run at the same time. Do not simply add every nameplate value; that can cause expensive oversizing. Do not use only an average either, because a short peak can pull receiver pressure below the minimum required by a critical machine.

Account for pressure losses and air quality

The compressor discharge setting is not the same as pressure at the machine. Filters, dryers, undersized pipe, long runs, fittings and elevation changes create pressure loss. Identify the lowest acceptable point-of-use pressure and work upstream through the system. Correct excessive losses rather than automatically increasing compressor pressure; higher pressure generally increases power demand and leakage flow.

Air-treatment equipment must be selected for the actual flow, inlet temperature, pressure and required air quality. See the compressed-air dryer selection guide before finalising the package.

Choose a sensible capacity allowance

A blanket 20–30% margin is common, but it is better to document what the allowance covers. Separate current production, measured leaks, approved expansion and uncertainty. Fix abnormal leakage rather than buying capacity to feed it. If future growth is uncertain, modular compressors, sequencing or space and electrical provision for a second unit may be more efficient than operating one oversized machine at poor part load.

Validate before ordering

• Measure flow or perform a load/unload study on an existing system.
• Log pressure at the compressor and critical points during a full production shift.
• Confirm FAD at the required pressure on the supplier data sheet.
• Review receiver storage, dryer capacity, filtration and pipe diameter.
• Compare control performance at expected minimum and maximum demand.
• Plan service access, ventilation and electrical supply.

Use ITT’s technical calculators as a planning aid, then validate the result with actual operating data.