Ametek 241CE II Operator's Manual page 83

For most applications, AMETEK recommends that the analyzer be operat-
ed with the Bypass Valve open, although applications with measurements
at pipeline pressures of 700 KPAG (100 PSIG) or less should be made with
the Bypass Valve closed. During the measuring cycle, the lower flow will
create pressure decreases throughout the sample system. At the low pipe-
line pressures, the decreases are significant enough to affect the accuracy
of the dewpoint measurement. When the analyzer is operated with the
Bypass Valve open, longer purging times are often required to effectively
clean the Measuring Cell between measuring cycles. Larger quantities of
liquids will also be condensed during the Cooling Stage.

When operating at very low pressures below 2000 KPA (300 PSIG)
and with large quantities of liquid droplets present in the gas stream,
NOTE
the flow through the drain Flow Restrictors in the Filterblock Assem-
bly may be insufficient to remove all liquid.
At low pressures, it is advisable to install an additional coalescing filter
with a valve or Flow Restrictor upstream of the analyzer to provide a
constant drain. Alternatively, a probe – such as a Genie – with an integral
filter can be used.
Each of the three sections that make up the Filterblock Assembly contains
a Flow Restrictor. The Flow Restrictors drain filtrate from the upstream
side of the filter and also provides a fast loop to improve measurement
response time. This ensures there will always be a fresh gas sample in the
Measuring Cell to coincide with any process changes that may occur dur-
ing any delay periods introduced during the measuring cycle. Therefore,
the response time is improved because the analyzer will not have to wait
for an older sample to be purged out.
When there are no liquids present in the stream, the combined flow
through the three Flow Restrictors in the Filterblock Assembly will be ap-
proximately 1.5 L/min (3.5 SCFH) at 7000 KPA (1000 PSI) of gas pressure. If
liquids are present, the flow through the restrictors will be slightly lower.
Installation and Start-Up
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