9 Cc Fm Conversion

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Section 9 - Technical Reference

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Page 9-8 1-410-712-4100

ACFM SCFM Conversion

Units of measurement are crucial when selecting vacuum equipment. ACFM and SCFM are

often confused, which can result in agrossly over-sized or under-sized vacuum system.

ACFM (Actual Cubic Feet per Minute) is the flow of a gas/vapor stream at the actual

measured pressure and temperature conditions. 500 ACFM @ 100oF and 24HgV is an example

of ACFM (volume occupied by gas flow under stated conditions).

SCFM (Standard Cubic Feet per Minute) is flow of a gas/vapor stream, where the temperature

and pressure are corrected to standard conditions. Standard temperature is usually considered60

oF, and standard pressure is usually 29.92HgAbs, (or 14.7 psia). SCFM is the volume the gas

would occupy if the mass flow were brought to standard temperature and pressure conditions.

Ideal gas laws govern the expansion and contraction of gases due to changes in pressure and

temperature. The Ideal Gas Law states:

PV = mRT, where:

P = pressure (HgA)

V = volume (CFM)M = mass (lb/min flow)

R = gas constant

T = temperature (oR)

All units must be compatible, and expressed in ABSOLUTE UNITS!

To convert ACFM to SCFM, and SCFM to ACFM, our formula can be simplified:

2

22

1

11

T

VP

T

VP =

To convert 500 ACFM @ 100oF and 24HgV to SCFM:

Solve for V1 (in SCFM)

where:

P1 = 29.92HgA (standard pressure in absolute units)

T1 = 520oR (standard Temperature in Absolute expressed in Rankin)

V2 = 500 ACFM

P2 = 5.92 HgA (29.92 24HgV)T2 = 560

oR (460 + 100)
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Page 9-9 1-410-712-4100

2

22

1

11

T

VP

T

VP =

=

2

1

1

2

21T

T

P

PVV

=

520

560

92.29

92.55001V

V1 = 106.54 SCFM

So, 500 ACFM @ 100oF and 24HgV is equal to 106.54 SCFM, which represents a factor of

4.69 to one. Selecting the wrong units of measure in this example could result in selecting a

system that was over-sized or under-sized by a factor of 4.69.

It becomes quite clear why the proper units must be used when sizing and specifying vacuum

systems. The greater the vacuum level, the greater will be the difference between ACFM andSCFM. Systems operating fairly close to atmospheric pressure may be more forgiving of error,

but the same principles still apply.


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Page 9-10 1-410-712-4100

SCFM ACFM Conversion Chart

(Above conversions based on 60oF air at sea level.)

To Convert from SCFM to ACFM:

1. Select pressure level from chart2. Multiply SCFM by Factor to get ACFM

To Convert from ACFM to SCFM:

1. Select pressure level from chart2. Divide ACFM by Factor to get SCFM

"HgV "HgAbs Torr Factor

0.00 29.92 760.0 1.00

1.00 28.92 734.6 1.03

2.00 27.92 709.2 1.07

3.00 26.92 683.8 1.11

4.00 25.92 658.4 1.15

5.00 24.92 633.0 1.20

6.00 23.92 607.6 1.25

7.00 22.92 582.2 1.31

8.00 21.92 556.8 1.36

9.00 20.92 531.4 1.43

10.00 19.92 506.0 1.50

11.00 18.92 480.6 1.58

12.00 17.92 455.2 1.67

13.00 16.92 429.8 1.77

14.00 15.92 404.4 1.8815.00 14.92 379.0 2.01

16.00 13.92 353.6 2.15

17.00 12.92 328.2 2.32

18.00 11.92 302.8 2.51

19.00 10.92 277.4 2.74

20.00 9.92 252.0 3.02

21.00 8.92 226.6 3.35

22.00 7.92 201.2 3.78

23.00 6.92 175.8 4.32

24.00 5.92 150.4 5.05

25.00 4.92 125.0 6.08

26.00 3.92 99.6 7.63

27.00 2.92 74.2 10.25

28.00 1.92 48.8 15.58

29.00 0.92 23.4 32.52

29.50 0.42 10.7 71.24

29.60 0.32 8.13 93.50

29.70 0.22 5.59 136.00

29.80 0.12 3.05 249.33

29.90 0.02 0.51 1496.00

29.91 0.01 0.25 2992.00


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Page 9-11 1-410-712-4100

SCFM ACFM Conversion Curves

The curves below present SCFM ACFM conversion in a graphical form. As with the chart on

the previous page, temperature is ignored in the conversion process. This is generally

acceptable, since temperature corrections to volume are generally in the 5% range withinambient temperature ranges (50

oF 90

oF). When temperatures are much higher or lower than

ambient, use the formulas to correct for both pressure andtemperature.

(Above conversions based on 60oF air at sea level.)

ACFM - SCFM Conversion Factors - (0 - 24 "HgV)

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

0 2 4 6 810

12

14

16

18

20

22

24

Inches of Mercury Vacuum

Fac

tor

ACFM - SCFM Conversion Factors -(24 - 29.5 "HgV)

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

24.0

24.5

25.0

25.5

26.0

26.5

27.0

27.5

28.0

28.5

29.0

29.5

30.0

Inches of Mercury Vacuum

Factor

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