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.