When comparing industrial air compressors, ask for free air delivery at the required pressure and stated reference conditions. Do not rank a delivered-flow rating against a displacement figure simply because both are printed in CFM. CFM describes a unit of volume per minute; it does not identify how the flow was obtained.
The useful purchasing question is not which quotation has the largest number. It is whether the two numbers describe the same output under comparable conditions. DFC Cari has not measured either compressor and does not provide a pressure-system test procedure.
What the two manufacturer explanations support
Atlas Copco’s USA technical explanation describes FAD as delivered air expressed at inlet or reference conditions and explains why those conditions matter. Quincy’s US glossary distinguishes FAD from theoretical displacement CFM. These educational pages were checked on October 5, 2026; neither supplies test evidence for your offered model.
Four figures that should remain separate
| Quoted term | What to identify | Buyer’s record |
|---|---|---|
| Displacement | Theoretical capacity basis | Do not relabel as delivered flow |
| Free air delivery | Delivered flow and reference conditions | Exact model sheet and rating pressure |
| CFM, l/s or m³/h | Unit attached to the figure | Original value and any documented conversion |
| Motor kW or hp | Input motor rating and scope | Separate from compressor airflow |
Build a comparable offer sheet
First, record the application’s required flow and pressure as provided by your responsible technical team. Preserve the demand assumptions, including whether the requirement represents continuous demand, a peak or a combined estimate. This article does not calculate that demand from a list of tools.
Second, request the manufacturer’s sheet for each exact compressor variant. Record the model, operating pressure, stated FAD, units, reference inlet conditions and cited test standard or edition, if supplied. Note whether filters, dryers or other components are included in the quoted package and where the performance boundary lies.
Third, mark any number whose basis is missing as unclassified. Ask the supplier to identify it in writing. Do not convert a displacement figure into FAD using an assumed efficiency, and do not fill in a missing pressure from a different variant’s brochure.
Fourth, convert units only after the measurement basis is aligned. Retain the original value beside the converted one and show the conversion used. A mathematically correct unit conversion does not repair a comparison between different reference conditions.
Use an explicit exception rather than a silent assumption
Suppose Offer A labels its flow as displacement, while Offer B labels its flow as FAD. This is a hypothetical document conflict, not a tested product comparison. Record the pair as not directly comparable and request delivered-flow evidence for Offer A on the same stated basis. The larger printed number is not the answer.
A new-machine performance sheet also does not establish the present output of a used compressor. Condition assessment and any appropriate professional performance verification remain separate from this quotation exercise.
What to carry into the purchase decision
Keep the aligned flow-pressure comparison, the unresolved conditions and the dated supplier response together. Energy consumption, air quality, installation and maintenance support deserve their own evidence rather than being inferred from FAD.
The DFC Cari machinery hub covers other specification checks. Our editorial preference is to leave an unknown visible until the supplier resolves it; this guide certifies no compressor and makes no suitability promise for a particular factory.
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