Vacuum - Flow Measurement
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!
| Pressure | Conversion Factor from scfm to acfm (or nl/s to al/s) | |||||||
|---|---|---|---|---|---|---|---|---|
| Temperature(oF) | ||||||||
| in Hg absolute | in Hg gauge | kPa absolute | 0 | 30 | 60 | 90 | 120 | 150 |
| 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 |
- T (oC) = 5/9 (T (oF) - 32)
- The calculation above is available as an excel file - vacuum.xls
- Altitude and pressure
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