> Hi all,
> A few months ago, just after I replaced several of the oil and vapor
> filters in our compressed air lines, we started having troubles with
> sample spinning on our Varian Unity 400 system. At first it was just slow
> to come up to speed so we tried the usual fixes like cleaning out the
> stack with a little EtOH on KimWipes, adjusting bearing air, etc. When
> that didn't work we moved on to things like replacing the yellow spinner
> mechanism in the leg, and re-adjusting the shim stack and probe
> positioning. At this point samples stopped spinning completely. Many
> times we would see an improvement for 2-3 days only to have it deteriorate
> again to a point where once again samples wouldn't spin. We then pulled
> out the stack and replaced all the O-rings, applied Teflon tape to
> threaded connections, rinsed the internal air lines with EtOH, and cleaned
> pretty much everything. Same result, a couple of good days then back to 0
> Hz. It's not a lack of spinner air because even when it doesn't spin we
> hear the spin air turning on.
> It seems we're just dancing around the problem. Even after the
> last, most thorough cleaning, a sample initially wouldn't spin (in the
> stack, outside the magnet), but we set it down for a few minutes to think
> about what to do next, and when we tried again it worked fine. It's
> incredibly frustrating, we don't see any rhyme or reason behind the
> problem, or our temporary fixes. It seems like there's something loose
> that can fall into a position to block air flow, or create leakage
> somewhere, but we just can't find it (we may have created this situation
> when we first started adjusting the stack). I thought it might be the
> bearing air that's only working intermittently, but if we run solvent
> through the bearing air line we consistently see it coming out all of the
> ports just fine.
> Any thoughts or insights would be greatly appreciated; we're all
> getting pretty tired of this problem.
>
> Sincerely,
>
> John T.
>
> Tomaszewski, John
> NMR Facility Coordinator
> Indiana University
> 800 E. Kirkwood Ave.
> Bloomington, IN 47405-7102
> (812) 855-4478
>
Received on Tue May 07 2002 - 16:19:54 MST
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