Brooks Instrument 5851E - Manual (Page 49)

Brooks ® Model 5851E
4-17
Section 4 Maintenance
Installation and Operation Manual
X-TMF-5851E-MFC-eng
Part Number: 541B104AAG
November, 2008
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 (
Δp) should be calculated as
follows:
P
in
Δp =
2
Δp =
Pressure drop (psi)
P
in
= Inlet pressure (psia)
If these conditions do not exist, pressure drop equals the inlet pressure
minus the outlet pressure.
64.7 psia
Is 44.7 psia < ? — No.
2
Then
Δp = 64.7 - 44.7 = 20psi
4. Using the nomograph, locate the pressure drop (psi) on the vertical line
marked " Δp" (Point A).
Figure 4-4 Example Nomograph