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Gas flow meter calculation formulas

Here you can find calculation formulas for gas flow conversions. Use the conversion formula shown below. Here’s also few examples to help you!

Gas flow conversion formula

Actual flow rate

Q0 = Actual flow rate

ρ0 = Specific gravity of measured gas (Air = 1)

p0 = Actual ABSOLUTE pressure in metering tube

T0 = Actual ABSOLUTE temperature
(Kelvin) in metering tube

(0°C = 273,15°K)
(20° C = 293,15°K)

Flowmeter design (calibration) conditions

Q1 = Flow meter reading

ρ1 = Specific gravity of design gas (Air = 1)

p1 = ABSOLUTE design pressure
(calibration pressure)

T1 = ABSOLUTE design temperature
(Calibration temperature)

Example 1

What is the maximum flow if flow meter EK-3NR is used for Carbon dioxide at 3 bar(g) / 25°C.

Ex-3NR scale is

  • 1 – 12 ln/min Air at 0 bar(g)/ 20°C

Q1 = 12 ln/min
ρ1 = 1
p1 = (0 + 1,013) bar = 1,013 bar
T1 = 293,15° K

Q0 = ?
ρ0 = 1,529
p0 = (3+ 1,013) bar = 4,013 bar
T0 = 298,15° K

Actual flow at 12 ln/min reading
Q0 = 19,15 ln/min CO2 at 3 bar(g)/ 25°C

Example 2

What is the actual flow if flow meter LH-JJ32 is used for Helium at 5 bar(g) / 10°C.

LH-JJ32 is calibrated for

  • 30 ln/min Nitrogen at 3 bar(g)/ 20°C

Q1 = 30 ln/min
ρ1 = 0,9672
p1 = (3 + 1,013) bar = 4,013 bar
T1 = 293,15°K

Q0 = ?
ρ0 = 0,1380
p0 = (5+ 1,013) bar = 6,013 bar
T0= 283,15°K

Actual flow at 30 ln/min reading
Q0 = 98,9 ln/min He at 5 bar(g)/ 10°C

Contact information

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Kytola Instruments Oy
P.O. Box 5
Olli Kytölän tie 1
FI-40951 Muurame
Finland

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