Dear isogeochemists,

Thanks all for your advice, both on and off line. I'd like to 
summarize the suggestions that were given to me, without naming names.

The problem: The rotary won't stop gurgling when trying to pump down 
after repair to one of the turbo pumps on a Delta Plus XP. Pumping 
aborts after 8 minutes because turbos can't reach 80% of their full speed.

The suggestions:
1) Check the ballast valve on the rotary pump (did it, was fine).
2) Degas the rotary pump (didn't do this - changed the rotary oil instead).
3) Check the oil wick and gasket on the turbo (didn't do this)
4) Let it go through the cycle of trying to pump down and timing out, 
then waiting for something to 'click' and try it again (the 'give it 
a chance, it'll figure it out' technique. Tried this one, no success.)
5) Check the screen between the inlet of the rotary pump and the rest 
of the vacuum plumbing. Clean it if oily (did this - it was an oily 
snarge. The thing still wouldn't pump down, however, after cleaning).
6) Check that the Penning Gauge is working properly (didn't try, but 
was on my list).
7) Check the seals on the down-to-air valve (took it out and reinstalled it).
8) Check that the down-to-air valve is actually functioning properly 
(wasn't sure how to do this - but the red light was on, indicating it 
was getting power and it did hiss whenever the pumps went off again 
after pumping for a while.)
9) Check the lights on the control module of the turbo pump - maybe 
the fault is there (All the happy lights were on and the not-happy 
lights were off).
10) Give the turbo a gentle whack (the 'teach it who's boss' 
technique? Was saving that for last.)
11) Make sure that the turbo is seated properly with the knive-edge 
gasket (did this with the source which I had had to pull out and 
twice with the turbo with no success. Tried once more with a 
brand-spankin-new seal on the turbo, and guess what? It worked!)

So in the end, it was my stupidity that caused it to fail. <<hanging 
head in shame>> Happily, though, I should be able to start running 
analyses again next week. Whew!!

Thanks to all who gave me suggestions! I hope this summary is helpful 
to others who may later have similar troubles.

~Penny


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                       Dr. Pennilyn Higgins
                        Research Associate

                             "SIREAL"
   Stable Isotope Ratios in the Environment Analytical Laboratory

         Department of Earth and Environmental Sciences
         University of Rochester
         227 Hutchison Hall
         Rochester, NY 14627

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