PN 903-8797, Rev A
Sample System Volume and Flow Rates
The sample gas ow rate during the Purging/Hold Stage is controlled by the
pressure regulator. The regulator may be set for the desired gas ow rate by
temporarily installing a ow metering device (e.g., a rotameter – supplied by
the customer/end user) on the Vent Line between the Filterblock 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 o. (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 ow rate to use, the line pressure, purging time,
and sample system volume should all be considered.
The dierence in pressure between the Measuring Cell and the ow metering
device must also be considered. The volume of the Measuring Cell is 7.3 mL;
the volume of the Measuring Cell, lter, and interconnecting line is approxi-
mately 23 mL. The volume of the remainder of the sample system can be
estimated from the length and inner diameter of the Sample 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 ow rates for various sample gas pressures are
listed below.
Do not exceed the pressure rating of the ow metering device.
Sample Gas Absolute Pressure Suggested Maximum Purge Flow Rate
KPA PSI L/minute 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
Installation and Start-Up | 2-39
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