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# Vacuum - Measure Flow

## 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!

Conversion Factor from scfm to acfm (or nl/s to al/s)
PressureTemperature (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

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Temperature

oC
oF

Length

m
km
in
ft
yards
miles
naut miles

Area

m2
km2
in2
ft2
miles2
acres

Volume

m3
liters
in3
ft3
us gal

Weight

kgf
N
lbf

Velocity

m/s
km/h
ft/min
ft/s
mph
knots

Pressure

Pa (N/m2)
bar
mm H2O
kg/cm2
psi
inches H2O

Flow

m3/s
m3/h
US gpm
cfm

3 30