User Manual SERVOPRO PLASMA Trace N
2
Analyzer
APPENDIX 1 58
2.4 Isolation valves
On figure 2, V1 to V4 represent isolation and purging valves. The key specifications for those
valves are:
• metal bellow or diaphragm valves (no packing)
• 1/8" tube compression fitting for port connections
• leak rate : 4 x 10
-9
atm cc/sec
• stainless steel
This type of valve is available from Parker or NUPRO Company. The V1 valve is used to isolate
the H
2
O trap when replacing the gas cylinder and the purging regulator. V2 is used for purging
the regulator. See section 3.0 for procedures on purging the pressure regulator.
2.5 Sample traps
Nearly all gas cylinders have trace amounts of water. We found some cylinders with more than
10 ppm of water! Moisture in the detector will not damage it, but will cause drift and instability,
which is something that we don't want and neither does the user. Another problem with that
moisture is the nitrogen may dissolve in it or may be retained by it. When the ambient
temperature of a sample line is increased the nitrogen is released, giving a temporarily higher
reading.
The only type of trap that we recommend is the T-3A-R available from Servomex. Almost all of
commercially available traps use molecular sieves with 5A or 13X. The use of such traps will
introduce a lot of drift and a long response time. Some of this nitrogen will be released when the
ambient temperature is increased. Conversely, when the ambient temperature is decreased the
nitrogen will be adsorbed by the trap, giving a lower reading.
We recommend one trap per cylinder and one on the sample line. The cylinder traps will last
longer than the one on the sample line; normally, calibration cylinders are replaced once or twice
a year. The trap is normally good for four cylinders. The one installed on the sample line may be
bigger. Your traps must not be exposed to temperature variations.
The traps are easily regenerated by putting them in an oven and reversing the gas flow direction.
See technical information included with your trap, or contact Servomex.
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