TheLogos
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Knf un840 ptfe diagphram vacuum pump
My apology in advance if this topic is too specific.
I recently acquire a knf un840 vacuum pump off ebay for $200. The unit is missing one hose barb on the side that sucks in air. The side that purges
the gas still has the hose barb.
All there is where the hose barb should be is a hole with threading on the inner diameter. The unit turns on and is functional. I just jam my tubing
in that hole and it sucks in air.
With no experience, I have no idea if this is worth keeping or if I should send it back. I talked to knf cs and they just said I have to send it to
them to be inspected and only then will a price quote be given. I gave them my email and phone number and never heard a thing again in a while.
What do you think I should do in this situation? I'm almost positive that its not working to full capability because there is some leak.
I don't want to epoxy anything permanently on there because it might need to be returned, and that might also compromise the chemical resistance of
the unit.
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zoombafu
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If you spent that much money and you think something is wrong you should send it back. I would just unscrew the hose barb from the output and put it
in the intake.
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TheLogos
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I tried but it won't come off easily. I might have to use a plier but only as a last resort since I might have to return it to them. I think the thing
might have been epoxied on.
I just don't know if I'm getting a good price on it enough to warrant keeping it. Most ptfe diagphram pump cost around $400 for an entry level model
from what I've seen, looking at vacuubrand, buchi and knf.
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bahamuth
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Take a picture of the pump centered on the missing barb, and measure the hole with a caliper and I'll tell you what kind of threads it has and might
even find you a substitute on ebay if I bother... Usually everything even in european countries has standard pipe threads (inches) and as such would
be easy to find a suitable substitute.
Any sufficiently advanced technology is indistinguishable from magic.
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bbartlog
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Seems like you could find a suitable fitting (male hose barb / male threaded end) somewhere online if you just determine the necessary dimensions. Not
that you don't have a case for sending it back, but it may be less hassle to just fix it yourself.
The less you bet, the more you lose when you win.
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Dr.Bob
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If the photo and description showed it missing the part, then you can't complain much, but I just looked at one of these for work, and they start at
$500 for the simplest one, so that is a reasonable deal. If the photo showed an intact model, I would ask the seller for the fitting.
You should be able to find a threaded adapter, if you find the thread size (find manual via google or knf website) and post it and the hose ID,
someone might be able to help you find a fitting. I might have one, I have everything else somewhere in my mess. I would try to swap fittings, use
an adjustable wrench or better yet a closed end wrench to avoid damaging it.
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TheLogos
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It was showed in the photo, but I did not know if it was supposed to be that way or not. Theres not a lot of info on google about scientific
instruments or photos. The seller didn't specifically state that anything was missing either.
I took the hose barb off of the purge valve and put it on the intake using a pair of pliers lined with napkin. It doesn't go on perfectly because
after looking at it closely, the thread was stripped.
Not sure what the diameter of the thread is, maybe 10mm, bigger than 3/8 for sure. I'm too broke to buy a caliper to measure. The manual only specify
the id of the barb and not the thread.
Also, I just assumed that the hose barb on fritted funnel is 3/8, but apparently not. It's something smaller, made by konte, chemglass and pyrex. So
where do I find teflon hosebarb adapter?
It's functional now, but I'm still going to press the seller to send me another teflon hose barb.
[Edited on 25-2-2012 by TheLogos]
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bahamuth
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Do you really need Teflon, polypropylene goes a long way, only thing I can thing of that might destroy PP is SO3, and I guess you won't put that
through your pump anyways so..
Any sufficiently advanced technology is indistinguishable from magic.
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MyNameIsUnnecessarilyLong
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I recommend you disassemble the pump heads and inspect the diaphragms (usually all you need to look at). Look if they show signs of tearing/separation
and degradation. If they're in bad shape you would probably save money to just return it. The diaphragms for pumps like that often cost $120+ each.
Edit: Or not. I just looked up how much those pumps cost. Paying another ~~250 for the diaphragms is still a good price tag. You could probably sell
it for at least 800 if you show buyers it has new-ish membranes.
[Edited on 2-29-2012 by MyNameIsUnnecessarilyLong]
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