Ametek 241CE II User Manual page 62

For most applications, AMETEK recommends that the analyzer be operated
with the Bypass Valve open, although applications with measurements at pipe-
line 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 pres-
sure decreases throughout the sample system. At the low pipeline 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.
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 during any delay periods
introduced during the measuring cycle. Therefore, the response time is im-
proved 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 approximately
1.5 L/minute (3.5 SCFH) at 7000 KPA (1000 PSI) of gas pressure. If liquids are
present, the flow through the restrictors will be slightly lower.
2-38 | 241CE II Hydrocarbon Dewpoint Analyzer
When operating at very low pressures below 2000 KPA (300 PSIG) and
with large quantities of liquid droplets present in the gas stream, the
flow through the drain Flow Restrictors in the Filterblock Assembly
may be insufficient to remove all liquid.
PN 903-8797, Rev A