Re: Maintaining a good vacuum
From: Pascal (u154388427_at_spawnkill.ip-mobilphone.net)
Date: 08/24/04
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Date: Tue, 24 Aug 2004 18:14:38 GMT
> Welch 1405
...
> the pump oil was very cloudy so I replaced with new oil.
Well, that's gotta help. You might want to replace it frequently for
a while to try to get everything contaminating the system out of there.
Compared to a new pump, oil is cheap.
Unless you think the cloudiness is due to aeration in which case
you've got a different problem.
Is this a commercial setup? Labconco? FTS? Or just a combination
or pump / cryo-cool / traps ... that you put together? SS connections
or rubber tubing?
> It only reached 60
> milliTorr. So now I'm trying to arrange to recharge of the
> refrigerant. Maybe that will help.
Can't you measure the temp? Although lower T will improve the
vacuum, if you just seal off the EMPTY (just air) system and leave
it to pump for a while, you should reach your ultimate vacuum.
Cooling the trap at that point might help a little, but not much.
Once you introduce volatiles, the trap is more important.
> Last week the system was pulling between 5 and 10 milliTorr which is
> better vacuum than the vacuum line system down the hall. With that
> level of vacuum I can do purification by vaccum sublimation of the
> expensive NMR spin label compounds I make. However, this week's 60
> milliTorr does not cut it.
I'd try changing the oil 2 or 3 times, letting it run hot for several hours
between changes. And I'll toss in the obvious: check your hoses and
fittings. Rubber tubing does wear out. Use the widest bore tubing that
you can. You can't pull max vacuum thru narrow ID tubing. Keep the
twists and turns to a minimum.
I don't know where (orifice? system?) or how you measured the pressure,
but the pump specs are at the orifice and once you add a "system" you'll
never get 10^-4 IN the system.
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- Next message: Wilco Oelen: "Re: Question: Reaction between copper (II) and copper (0) in concentrated HCl"
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