Brooks
®
Model 5850i
4-16
Section 4 Maintenance
Installation and Operation Manual
X-TMF-5850i-MFC-eng
Part Number: 541B108AAG
November, 2008
Example: What is the air equivalent flow rate of 2000 sccm Hydrogen?
In order to calculate the orifice conversion factor when using a gas mixture,
the following formula must be used:
Where P1
=
percentage by volume of gas 1
P2
=
percentage by volume of gas 2
Pn
=
percentage by volume of gas n
Example: Find the Air equivalent flow for 20 slpm of a 20% Helium
and 80% Chlorine gas mixture.
Q
AIR
=
Q
gas
(orifice conversion factor)
=
20 x 1.417
=
28.34 slpm air
2. If inlet and outlet pressures are given in gauge pressure (psig)
add14.7 to convert to absolute pressure (psia).
Outlet Pressure — 30 psig + 14.7 = 44.7 psia
Inlet Pressure — 50 psig + 14.7 = 64.7 psia
3. Determine Critical Pressure Drop
Critical pressure drop occurs when the outlet pressure (psia) is less
than half the inlet pressure (psia) or
P outlet
<
P inlet
2
If these conditions exist, the pressure drop (
Δ
p) should be calculated as
follows: