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An added concern with Turbo pumps, particularly in the context of earlier
messages contributed to this discussion, is that they wear out fast when
used on a fluorination line, even when efforts are made to protect them
from corrosive vapors.  We have had good experiences with very large ion
pumps taken off old thermal ionization machines.  These are rare items but
if you can get them you will find they reach incredibly low baseline
pressures compared to the norm for stable isotope lines.

John Eiler

>At 07:09 AM 1/26/01 -0700, you wrote:
><snip. . .
>
>>For most sample preparations, a better quality fore-pump plus a molecular
>>sieve trap or equivalent serves the purpose. If lower pressure is required,
>>one can use an oil diffusion pump or a turbomolecular pump.
>>Roy Krouse
>>
>
>I want to strongly second Roy Krouse's opinion.  When we set up our vacuum
>line a few years ago, I chose a turbomolecular pump because of
>environmental and health concerns.  With a mercury pump, if the line
>suffered a crack or break, the entire thing would have to be disassembled
>and cleaned before our glassblower would work on it - a major pain with
>lots of down time.
>
>The only drawback, - the turbomolecular pump is a pricey option and may not
>be practical for every lab in every setting.  As an added advantage, the
>turbomolecular pump offers huge advantages in pumping time over a mercury
>diffusion pump, so if processing time is important, there might be some
>cost savings there.
>
>
>Regards,
>   -Mark Schurr
>
>*************************************************
>Mark R. Schurr, Ph.D., R.P.A    Phone:  (219) 631-7638
>Assistant Professor                     FAX:     (219) 631-8209
>Department of Anthropology              http://www.nd.edu/~mschurr
>University of Notre Dame
>Notre Dame, IN  46556 USA