Reference · Sizing & specs
How to Read a CAGI Data Sheet
The short answer: A CAGI data sheet is a one-page standardized performance sheet published per compressor model — third-party-verified for tested machines, manufacturer-tested but not third-party-verified for others. The nine fields that matter most are full-load BHP, full-load SCFM at rated PSI, specific power (kW/100 CFM), part-load specific-power curve, no-load BHP, rated PSI, control type, ambient conditions assumed, and package noise. The “no-load BHP” line is the one operators most often overlook — it tells you what the compressor costs when it’s idling between cycles.
What CAGI sheets are
The Compressed Air & Gas Institute (CAGI) is the industry body that maintains a standardized performance-reporting format for rotary compressors. Manufacturers publish one PDF per model, in a defined layout, with performance figures tested at ISO 1217 Annex C reference conditions: 14.5 PSIA inlet, 68 °F inlet temperature, 60% relative humidity. The standardization lets buyers compare two compressors apples-to-apples without needing to translate from one manufacturer’s marketing prose to another’s.
CAGI also operates the Performance Verification Program — voluntary third-party testing of submitted compressors. A compressor that passes carries a CAGI verification seal on its data sheet, which means the published figures have been independently witnessed. Not all compressor models go through verification; some manufacturers publish CAGI-format sheets with their own internal test data. Look for the seal.
The nine fields that matter
1. Full-load brake horsepower (BHP)
The mechanical power the airend consumes when delivering rated SCFM at rated PSI. This is not the motor nameplate HP — nameplate HP is the motor’s rated output, BHP is what the airend actually requires. For most rotary screws, BHP is 90–95% of nameplate HP at the design operating point, with motor losses making up the rest.
Why it matters: BHP is the basis for energy-cost calculations. Multiply BHP × 0.746 = kW input to the airend; divide by motor efficiency (0.94–0.96) for total electrical input.
2. Full-load SCFM at rated PSI
How much standardized cubic feet per minute the compressor delivers at the rated pressure. “Standardized” means corrected to sea level, 68 °F, 0% humidity reference conditions — so the number is comparable across machines tested under different conditions.
Watch the rated PSI closely. A compressor’s SCFM at 100 PSI is significantly higher than the same machine’s SCFM at 175 PSI. Cross-shopping requires comparing at the same pressure point.
3. Specific power (kW per 100 CFM)
The headline efficiency number. Calculated as kW input to the compressor package divided by SCFM delivered, then normalized to 100 CFM. Lower is better. For modern oil-flooded screws at 125 PSI:
- Best-in-class: 17–19 kW/100 CFM
- Average: 20–22 kW/100 CFM
- Older or budget designs: 24–27 kW/100 CFM
The difference between 18 and 22 kW/100 CFM is 22% more energy. Over a 10-year operating life on a 100 HP plant, that’s $40,000–$80,000 in energy cost. Specific power is the single number that justifies the higher capital cost of a premium machine over a budget alternative.
4. Part-load specific power (often a graph)
The most-overlooked field. Specific power degrades as the compressor runs at less than full load — modulating compressors degrade fastest, load/unload compressors degrade more gracefully, VSD compressors stay nearly flat. The CAGI sheet usually presents this as a graph showing specific power at 25%, 50%, 75%, and 100% of rated capacity.
Why it matters: if your plant runs at 50% average load, the 100% specific-power number is irrelevant — what you’ll actually pay for is the 50% specific power. A compressor with great 100% specific power but poor part-load behavior costs more than its data sheet implies. See the modulating vs load/unload guide for the energy curves.
5. No-load BHP (the unload-running cost)
The mechanical power consumed by the airend when the inlet is closed and the compressor is running unloaded. Typically 25–35% of full-load BHP for an oil-flooded screw. This is the number that drives unload running cost, and it’s the single most-overlooked field on the sheet.
For a 50 HP screw with a no-load BHP of 17 (35% of 48 full-load BHP), at $0.12/kWh, every 1,000 hours of unloaded operation costs ~$1,500. A plant at 30% duty unloads for ~2,800 hours/year — costing $4,200/year purely on no-load draw. This is data the manufacturer publishes and that few operators read.
6. Rated pressure (PSI)
The pressure point at which the SCFM, BHP, and specific-power figures are quoted. Most rotary-screw data sheets are quoted at 100, 110, 125, or 150 PSI. A 7.5 HP screw rated at 100 PSI delivers significantly more SCFM than the same machine rated at 150 PSI.
Beware of cross-shopping at different pressure ratings — convert to a common basis. As a rough rule, each 10 PSI of pressure increase reduces SCFM by 4–5% on a typical screw.
7. Control type
Modulating, load/unload, variable-speed, or modulating with shutdown (auto-dual). Determines which part-load specific-power curve applies. Critical for matching the compressor to plant duty profile.
8. Ambient conditions assumed
All CAGI figures are at ISO 1217 reference: 68 °F inlet, 60% relative humidity, sea-level pressure. Real installations deviate. Hot inlet air (above 90 °F) reduces SCFM by 1–2% per 10 °F because the air is less dense. High humidity reduces SCFM by 1–3% because some intake displacement is water vapor that won’t compress. High altitude reduces SCFM by 3–4% per 1,000 ft elevation. Real installed performance is often 5–10% below CAGI rating.
9. Package noise (dBA at 1 meter)
Important for installation siting. A sound-attenuated rotary screw runs 65–75 dBA at 1 meter; an industrial piston runs 80–95 dBA. OSHA exposure limits and floor-plan adjacency considerations both come back to this number.
Common gotchas
Manufacturer-tested vs CAGI-verified
The CAGI logo and the CAGI verification seal are different things. Any manufacturer can publish a sheet in CAGI format; only verified sheets carry the verification mark. Verified data is independently tested at a CAGI-accredited lab. Unverified data is the manufacturer’s own; it may or may not match field performance.
Look for the verification seal on any compressor over 25 HP — the manufacturers in that segment generally compete on energy efficiency and almost all submit for verification. Below 25 HP, verification is rare; rely on manufacturer reputation and warranty terms.
“Rated SCFM” vs “delivered SCFM”
Some manufacturers publish “rated” or “nominal” SCFM in their marketing brochures that differs from the CAGI-sheet delivered SCFM. The marketing figure is usually quoted at the compressor’s most-flattering pressure point or ambient condition; the CAGI delivered figure is at ISO 1217 reference. Always pull from the CAGI sheet, never from the brochure.
Specific-power-only comparisons can mislead
Specific power is a per-CFM metric; it doesn’t capture absolute output capacity. Cross-shopping a 100-CFM screw against a 150-CFM screw on specific power alone ignores that the smaller machine can’t meet the larger duty. Match capacity first, then optimize on specific power among machines of comparable rated capacity.
Heat-of-compression isn’t on the sheet
The CAGI sheet doesn’t list air-temperature rise across the airend or the heat available for heat recovery. For energy-recovery projects, you need the manufacturer’s supplementary data — typically ~80% of full-load BHP becomes recoverable heat in the cooler discharge.
How to compare two compressors using only the CAGI sheet
- Confirm both sheets are at the same rated PSI. If not, normalize: each 10 PSI of difference is ~4–5% SCFM change.
- Compare full-load SCFM at the same PSI. Larger is more capacity.
- Compare full-load specific power (kW/100 CFM). Lower is more efficient.
- Compare part-load specific power at the duty cycle your plant actually runs. This is where the headline efficiency story can flip.
- Compare no-load BHP as a fraction of full-load. Lower fraction = lower unload running cost.
- Compare package noise for installation siting.
- Verify both are CAGI-verified (look for the seal). If one is and one isn’t, you’re comparing tested data to manufacturer claims; weight accordingly.
Real-world examples from the catalog
Among the rotary screws we list, Quincy QGS-7.5 publishes a CAGI sheet showing 20.4 SCFM at 150 PSI; the Ingersoll Rand R5.5i-125 sheet shows 27.5 SCFM at 125 PSI. Both are at the same general capacity class, but the rated-PSI difference (150 vs 125) means you need to normalize before declaring one larger. The Atlas Copco GA5-125 at 28 SCFM/125 PSI and the Atlas Copco GA7-125 at 41.6 SCFM/125 PSI sit cleanly on the same pressure rating, which makes them direct cross-shop candidates by SCFM. The Kaeser CSD 75 at 461 SCFM/110 PSI is its own capacity class.
For piston compressors, CAGI sheets are less common — most piston manufacturers publish a simpler one-page spec card that’s not in CAGI format. Pressure-lubricated industrial pistons (the Quincy QR-25 Model 5120at 87 SCFM/175 PSI being one example) sometimes have CAGI sheets, but the verification rate is much lower than for rotary screws.
Common questions
Where do I find CAGI sheets?
Manufacturer websites under each model’s specification page. CAGI also maintains a public archive at cagi.org with searchable sheets for verified models. For non-CAGI-verified compressors, the manufacturer’s spec PDF is the equivalent — usable, but treat the numbers as manufacturer-claimed rather than independently tested.
What does “package efficiency” mean on the sheet?
Package efficiency is the inverse of specific power, expressed as a percentage. Higher is better. A compressor at 18 kW/100 CFM has package efficiency around 70%; one at 22 kW/100 CFM is around 57%. The package figure includes motor, drive, airend, and parasitic losses — everything the compressor pulls from the wall, divided by what it delivers as compressed air to the discharge flange.
Is the CAGI sheet binding on the manufacturer?
If CAGI-verified, yes — the manufacturer warrants delivered performance against the verified figures within ±5%. For unverified sheets, performance claims are manufacturer’s word; warranty terms govern.
Does CAGI test reciprocating compressors?
CAGI’s primary scope is rotary positive-displacement (screw and vane) and dynamic (centrifugal) compressors. Reciprocating piston compressors have their own performance-reporting tradition — typically a manufacturer’s spec card with ACFM at rated PSI rather than the SCFM-and-specific-power format CAGI uses for screws. The fundamental fields (capacity, power, pressure, noise) are equivalent; the format and the verification program differ.
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