4-9
Brooks
®
Model 5860
i
Section 4 Maintenance
Installation and Operation Manual
X-TMF-5860i-MFM-eng
Part Number: 541B110AAG
November, 2008
It is generally accepted that the mass flow rate derived from this equation
is only accurate to ±5%. The sensor conversion factors given in Table 4-3
are calculated based on a gas temperature of 21°C and a pressure of one
atmosphere. The specific heat of most gases is not strongly pressure and
temperature dependent, however gas conditions that vary widely from
these reference conditions may cause an additional error due to the
change in specific heat due to temperature and/or pressure.
4-6 Restrictor Sizing
The restrictor assembly is a ranging device for the sensor portion of the
flowmeter. 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
meters with different full scale flow rates. For a discussion of the
interaction of the various parts of the meter, 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 flowmeter 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
S778D017AAA) Restrictor O-ring, refer to the spare parts Section 5, for
the correct part number.
Restrictors
The Model 5860
i
Series Mass Flowmeters use two types of restrictor
assemblies depending on full scale flowrate.
1. Sintered wire mesh for Nitrogen equivalent flow rates above 3.4
slpm. These restrictor assemblies are made from a cylinder of
sintered wire mesh and are easily cleaned if they become
contaminated in service.
2. Anti-Clog Laminar Flow Element (ACLFE). This type of restrictor
assembly is used for Nitrogen equivalent flow rates less than 3.4
slpm.
Sizing
All Model 5860
i
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 Model 5860
i
Series Mass Flowmeters is shown in
Table 4-4.
