MKS Mass-Flo 1479A, Instruction Manual, Page: 65 / 72

Appendix C: MFC Sizing Guidelines How To Determine the Valve Configuration
55
Example
Suppose you need to flow boron trichloride at a rate of 250 sccm and the inlet pressure is 20 psia.
Your process runs at atmospheric pressure, so the differential pressure is 5 psid.
1. Determine the maximum flow factor (Cv) for the gas of interest, using the equation listed
in step 1, page 53.
The Gas Density for boron trichloride, listed in Appendix B: Gas Correction Factors,
page 47, is 5.227. The Cv Pressure Factor, read from Table 9, page 53, for a 20 psia
inlet and
5 psid differential pressure, is 0.373. Therefore, our equation becomes:
C
V
(max) = 250 sccm
1.293
5.227
( )
( )
( )
0.373
Cv =187.5
2. Select the valve configuration with a Cv value that is closest to, though larger than, the
Cv value calculated in step 1.
A Cv value of 187.5 falls between 122.11 (configuration 6) and 244.22 (configuration 7).
To ensure that the unit can deliver the 250 sccm flow, choose configuration 7.