Conversion Curves for Gases

If more convenient, approximate correction factors may be determined using the following formulas.

A. Pressure:

where
Q₁ = Observed flowmeter reading
Q₂ = Actual flow corrected for pressure
P₁ = Actual pressure, 14.7 PSI + pressure in PSI inside flowmeter. Measured at outlet on all but TMV units, Inlet pressure on TMV models.
P₂ = Standard atmospheric pressure, 14.7 PSI

B. Specific Gravity:

where
Q₁ = Observed flowmeter reading
Q₂ = Actual flow corrected for specific gravity
1 = Specific gravity of air
S.G. = Specific gravity of gas being used in flow meter originally calibrated for air.

NOTE: The corrections shown in the curves and in the formulas are for variations in specific gravity and internal pressure* only. Further correction may be necessary for variations in viscosity and changes in type of flow from laminar to turbulent or vice versa. This is particularly true in the case of extremely low flows of the lighter gases. Nevertheless these charts and correction factors can be quite useful when dealing with small changes in pressure* and specific gravity.

*Measured at discharge on all but TMV units. Inlet pressure on TMV models.