ACFM AND SCFM CORRECTIONS FOR ALTITUDE OIL-FREE,
TWO-STAGE ROTARY SCREW AIR COMPRESSORS 100 PSIG DISCHARGE PRESSURE

Altitude Above MSL Feet PSIA ACFM
Correction Factor		 Ambient Temp. Deg. F Ambient R.H. Percent Inlet
Pg, H2O
PSIA		 SCFM
Correction Factor		 Total Correction Factor Reduction in BHP Percent
0 14.7 1.0000 68 36 .3389 1.0000 1.0000 0
1000 14.18 .9998 64 36 .2995 .9718 .9716 1.1
2000 13.66 .9995 61 36 .2641 .9438 .9433 2.9
3000 13.17 .9991 57 36 .2325 .9164 .9156 4.7
4000 12.69 .9988 54 36 .2042 .8899 .8888 6.3
5000 12.23 .9985 50 36 .1791 .8636 .8623 8.0
6000 11.78 .9982 47 36 .1567 .8383 .8368 9.5
7000 11.34 .9979 43 36 .1368 .8133 .8116 11.1
8000 10.90 .9976 39 36 .1191 .7878 .7860 12.6
9000 10.49 .9974 32 36 .1035 .7638 .7618 14.0
10000 10.10 .9971 32 36 .0898 .7408 .7386 15.4

*Typical ambient at elevated altitude. For different temperatures and R.H.’s, see formula page.

ACFM CORRECTION DUE TO ALTITUDE

Ambient pressure drops as altitude increases, increasing the pressure ratio across the compressor. The increased pressure ratio reduces the volumetric efficiency slightly, reducing the ACFM, as shown in Table 2. Table 2 is for a two-stage, oil-free rotary screw compressor.

SCFM CORRECTION DUE TO ALTITUDE AND TEMPERATURE EFFECTS

The reduced pressure at altitude decreases the density of the inlet air, reducing the amount of “standard air” delivered. In addition, ambient temperature drops as altitude increases. Temperature effects two aspects of a compressor’s throughput of air. First, it effects the density of the air at intake, varying the amount of standard air delivered. Secondly, cooler inlet air holds less moisture than standard air does (68 deg. and 36% humidity), and warmer air holds more, effecting the amount of delivered standard air.