Varian 4000 GC, Hardware Operation Manual

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5. If there are no air or water leaks in your system, you should obtain the
following approximate values. Actual values may vary from system to
system.
Base Amount TIC 18:28 ratio 19:18 ratio 28 width
<500 <5000 ~ 1:1 10 to 15% < 1 m/z
An air/water spectrum obtained from a system with a small air leak and little
water vapor is indicated by:
•
The peak height at mass 28 is noticeably greater than that at mass 18.
•
The base amount value has increased to greater than 500.
•
The ratio of the peak height at mass 18 to that at mass 19 is greater than
or equal to 10:1.
An air/water spectrum obtained from a system with a moderate air leak and
little water vapor is indicated by:
•
The peak at 28 starts to overload.
•
The Base Amount value may be several thousand counts.
An air/water spectrum obtained from a system with a large air leak and little
water vapor is indicated by:
•
The peaks at masses 18, 19, 28 and 32 are broadened. As a leak
increases, all peaks broaden and eventually become undifferentiated.
Fixing a Large Air Leak
Typical sources of large air leaks are
•
Particles or damage on the manifold flange O-ring seal.
•
Particles or damage on the transfer line O-ring seal.
•
The transfer line brass nut is loose.
•
Poor O-ring sealing between the turbomolecular pump and the manifold.
Do not over tighten the fittings; otherwise, you may generate an even larger
leak.
If you cannot eliminate the leak, vent the system, and check the O-ring on the
manifold and transfer line for particles. Wipe off both O-rings with lint-free cloth.
The turbomolecular pump will probably fail to achieve its 100% speed if there is a
leak or poor seal at the turbo/manifold interface. Never attempt to operate the
system under these conditions.
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