ACFM AND SCFM CORRECTIONS FOR ALTITUDE OIL-FLOODED
SINGLE-STAGE ROTARY SCREW AIR COMPRESSOR

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 .9984 64 36 .2995 .9718 .9703 1.8
2000 13.66 .9969 61 36 .2641 .9438 .9409 3.5
3000 13.17 .9954 57 36 .2325 .9164 .9122 5.2
4000 12.69 .9940 54 36 .2042 .8899 .8845 6.9
5000 12.23 .9926 50 36 .1791 .8636 .8572 8.5
6000 11.78 .9912 47 36 .1567 .8383 .8309 10.1
7000 11.34 .9989 43 36 .1368 .8133 .8124 11.6
8000 10.90 .9887 39 36 .1191 .7878 .7789 13.1
9000 10.49 .9874 32 36 .1035 .7638 .7542 14.6
10000 10.10 .9862 32 36 .0898 .7408 .7305 16.1

*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 Tables 1. Table 1 is for a single-stage, oil-flooded rotary screw compressor, while

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.