4-19
Brooks
®
Model 5850i
Section 4 Maintenance
Installation and Operation Manual
X-TMF-5850i-MFC-eng
Part Number: 541B108AAG
November, 2008
conditions. If this point is between two orifice sizes, select the next
largest size orifice to ensure adequate flow. If the orifice selected
falls below .0013, choose .0013 size orifice.
For this example the .007 size orifice would be selected.
4-7 Restrictor Sizing
The restrictor assembly is a ranging device for the sensor portion of the
controller. It creates a pressure drop which is linear with flow rate. This
diverts a sample quantity of the process gas flow through the sensor. Each
restrictor maintains the ratio of sensor flow to restrictor flow, however the
total flow through each restrictor is different. Different restrictors (micron
porosity and active area) have different pressure drops and produce
controllers with different full scale flow rates. For a discussion of the
interaction of the various parts of the controller, you are urged to review
Section 3-1 (Theory of Operation).
If the restrictor assembly has been contaminated with foreign matter, the
pressure drop vs. flow characteristics will be altered and it must be cleaned
or replaced. It may also be necessary to replace the restrictor assembly
when the mass flow controller is to be calibrated to a new flow rate.
Restrictor assembly replacement should be performed only by trained
personnel. The tools required for the removal/replacement procedure are
as follows:
Appropriate size wrench for the removal of the inlet process connection
Restrictor removal tool
(contained in service tool kit P/N S-778-D-017-AAA)
Restrictor O-ring, refer to the spare parts Section 5, for the correct
part number.
Restrictors
The 5850 Series Mass Flow Controllers use two types of restrictor
assemblies depending upon full scale flowrate.
1. Anti-Clog Laminar Flow Element (ACLFE). This type of restrictor
assembly is used for air equivalent flow rates less than 3.4 slpm.
2. Sintered wire mesh for air equivalent flow rates above 3.5 slpm.
These restrictor assemblies are made from a cylinder of sintered
wire mesh and are easily cleaned if they become contaminated in
service.
Sizing
All 5850 Series Restrictor Assemblies are factory adjusted to provide a 115
mm water column pressure drop for a specific flow rate. This corresponds
to the desired full scale flow rate. A list of restrictor assemblies used in the
5850 Series Mass Flow Controllers is shown in Table 4-5.
