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# Vacuum - Flow Measurement

## Measure air volume flow in vacuum.

For standard or normal pressure it is common to measure flow in

• standard cubic feet minute - scfm - imperial units
• normal metric liter per second - nl/s - metric units

In vacuum the air or gas is expanded and it is common to use

• actual cubic feet minute - acfm - imperial units
• actual metric liter per second - al/s - metric units

Since the gas is expanded, actual volume flow is greater than standard volume flow for the same amount of gas.

The flow volume can be converted from standard volume flow to actual volume flow by the expression:

qa = qs (29.92 / p) ((t + 460) / 520)                                  (1)

where

qa= actual volume flow (acfm)

qs= standard volume flow (scfm)

p= actual pressure (in Hg)

t= temperature (oF)

For full table - rotate the screen!

Vacuum - Flow Measurement Conversion Factor
PressureConversion Factor from scfm to acfm (or nl/s to al/s)
Temperature(oF)
in Hg absolutein Hg gaugekPa absolute0306090120150
29.92 0.00 101.42 0.88 0.94 1.00 1.06 1.12 1.17
28.92 1.00 98.03 0.92 0.97 1.03 1.09 1.15 1.21
27.92 2.00 94.64 0.95 1.01 1.07 1.13 1.20 1.26
26.92 3.00 91.25 0.98 1.05 1.11 1.18 1.24 1.30
25.92 4.00 87.86 1.02 1.09 1.15 1.22 1.29 1.35
24.92 5.00 84.47 1.06 1.13 1.20 1.27 1.34 1.41
23.92 6.00 81.08 1.11 1.18 1.25 1.32 1.40 1.47
22.92 7.00 77.69 1.15 1.23 1.31 1.38 1.46 1.53
21.92 8.00 74.31 1.21 1.29 1.36 1.44 1.52 1.60
20.92 9.00 70.92 1.27 1.35 1.43 1.51 1.60 1.68
19.92 10.00 67.53 1.33 1.42 1.50 1.59 1.68 1.76
18.92 11.00 64.14 1.40 1.49 1.58 1.67 1.76 1.86
17.92 12.00 60.75 1.48 1.57 1.67 1.77 1.86 1.96
16.92 13.00 57.36 1.56 1.67 1.77 1.87 1.97 2.07
15.92 14.00 53.97 1.66 1.77 1.88 1.99 2.10 2.20
14.92 15.00 50.58 1.77 1.89 2.01 2.12 2.24 2.35
13.92 16.00 47.19 1.90 2.03 2.15 2.27 2.40 2.52
12.92 17.00 43.80 2.05 2.18 2.32 2.45 2.58 2.72
11.92 18.00 40.41 2.22 2.37 2.51 2.65 2.80 2.94
10.92 19.00 37.02 2.42 2.58 2.74 2.90 3.06 3.21
9.92 20.00 33.63 2.67 2.84 3.02 3.19 3.36 3.54
8.92 21.00 30.24 2.97 3.16 3.35 3.55 3.74 3.93
7.92 22.00 26.85 3.34 3.56 3.78 4.00 4.21 4.43
6.92 23.00 23.46 3.82 4.07 4.32 4.57 4.82 5.07
5.92 24.00 20.07 4.47 4.76 5.05 5.35 5.64 5.93
4.92 25.00 16.68 5.38 5.73 6.08 6.43 6.78 7.13
3.92 26.00 13.29 6.75 7.19 7.63 8.07 8.51 8.95
2.92 27.00 9.90 9.06 9.66 10.25 10.84 11.43 12.02
1.92 28.00 6.51 13.79 14.68 15.58 16.48 17.38 18.28
0.92 29.00 3.12 28.77 30.65 32.52 34.40 36.27 38.15
0.82 29.10 2.78 32.28 34.38 36.49 38.59 40.70 42.80
0.72 29.20 2.44 36.76 39.16 41.56 43.95 46.35 48.75
0.62 29.30 2.10 42.69 45.47 48.26 51.04 53.83 56.61
0.52 29.40 1.76 50.90 54.22 57.54 60.86 64.18 67.50
0.42 29.50 1.42 63.02 67.13 71.24 75.35 79.46 83.57
0.32 29.60 1.08 82.71 88.11 93.50 98.89 104.29 109.68
0.22 29.70 0.75 120.31 128.15 136.00 143.85 151.69 159.54
0.12 29.80 0.41 220.56 234.95 249.33 263.72 278.10 292.49

## Related Topics

• ### Gases and Compressed Air

Properties of air, LNG, LPG and other common gases. Pipeline capacities and sizing of relief valves.

## Related Documents

• ### Vacuum

Vacuum is defined as air pressure below atmospheric pressure.
• ### Vacuum - Air Expansion Ratio

Convert vacuum air volume to standard air volume
• ### Vacuum - Evacuation Time

Vacuum pumps - calculate flow rate and required evacuation time.
• ### Vacuum Pipes - Flow Velocities

Air velocity diagrams for vacuum pipe lines.
• ### Vacuum Pipes - Pressure Loss vs. Air Flow

Calculate pressure drops in vacuum pipe lines.
• ### Vacuum Pumps - Exhaust Pipe Capacities

Capacities of vacuum pump exhaust pipes.

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## Citation

• The Engineering ToolBox (2005). Vacuum - Flow Measurement. [online] Available at: https://www.engineeringtoolbox.com/vacuum-flow-measurement-d_836.html [Accessed Day Month Year].

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8.21.8

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