3-40 | Model 241CE II Hydrocarbon Dewpoint Analyzer
Sample System Volume and Flow Rates
The sample gas flow rate during the Purging/Hold Stage is controlled by
the pressure regulator. The regulator may be set for the desired gas flow
rate by temporarily installing a flow metering device (e.g., a rotameter
– supplied by the customer/end user) on the Vent Line between the Filter-
block Assembly and the used gas disposal location.
The rotameter can be a permanent installation if it is rated and ap-
proved for the pressure it will be exposed to when the Vent Line is
closed off. (Example, if the Vent Line is closed, the rotameter must be
able to withstand the pressure of the process line.)
If the rotameter being used cannot withstand the process gas line
pressure, it must be a temporary installation only; the rotameter
must be removed before running the analyzer under normal operating
conditions.
When determining the purge flow rate to use, the line pressure, purging
time, and sample system volume should all be considered.
The difference in pressure between the Measuring Cell and the flow me-
tering device must also be considered. The volume of the Measuring Cell
is 7.3 mL; the volume of the Measuring Cell, filter, and interconnecting
line is approximately 23 mL. The volume of the remainder of the sample
system can be estimated from the length and inner diameter of the Sam-
ple Line. The volume of 0.25-inch tubing having 0.035-inch wall thickness
is 16.4 mL/m (5.0 mL/ft). The maximum suggested purge flow rates for
various sample gas pressures are listed below.
Do not exceed the pressure rating of the flow metering device.
Sample Gas Absolute Pressure Suggested Maximum Purge Flow Rate
KPA PSI L/min SCFH
700 100 1.0 2
2000 290 2.0 4
3000 435 2.5 5
4000 580 3.0 6
5000 725 3.5 7
7500 1088 5.0 10
10000 1450 7.5 15
13790 2000 10.0 20
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WARNING
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WARNING
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