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Author: Subject: Vacuum Pump Foibles
weilawei
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[*] posted on 3-12-2017 at 12:23
Vacuum Pump Foibles


I recently purchased a quite nice and proper rotary vane pump after years of lusting after one (and saving up for the enormous sticker shock). Now, I'm testing it out, but I've run into some unexpected issues: namely, my heavy wall Tygon tubing collapses under full vacuum. Now, I added a gas inlet (and have H2O boiling at 35 C), but I can still only pull down to ~43 Torr at the apparatus. The pump is capable of pulling 13 millitorr, but I can't run it wide open. Should I redo my foreline in steel, or is there any better way to get the vacuum down lower without buying steel vacuum tubing? I'm considering a KF25 steel pipe with the hose barb directly hooked to the cow via 2 inches of Tygon to make a glass barb to metal barb seal.

EDIT: At the pump, one gage reads 25 Torr, and another reads 4.3 Torr (the number given above is calculated from the BP). Also, in the setup, there's no cold trap, but the condenser seems to work quite well, and I'm running it with a gas ballast to avoid condensation in the pump. I do have a cold trap, but it's not hooked up due to needing a CO2 tank for dry ice (also limiting my use to basic testing at the moment).

[Edited on 3-12-2017 by weilawei]

20171203_152656.jpg - 1.6MB

[Edited on 3-12-2017 by weilawei]

[Edited on 3-12-2017 by weilawei]
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NEMO-Chemistry
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[*] posted on 3-12-2017 at 15:00


You can get heavy duty vac tubing, i dont always use a cold trap. But i do always try and use a wash bottle for acids, i change my oil with compressor oil roughly every 6 weeks depending on use, its really cheap from some places.

Also sometimes i use a wash bottle filled with engine oil, i figure most the crap will get caught in that. But changing the oil often is your best bet.
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weilawei
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[*] posted on 3-12-2017 at 16:23


It seems I purchased Tygon with a 7/16" OD instead of 7/8". There's quite a difference in price--and performance, it would seem. North of $10/ft! I'll look into ordering some after the holidays, and hopefully that will solve my issue. I should be good down to 1 Torr (it says it's rated for 759 mm Hg max. vacuum.).

[Edited on 4-12-2017 by weilawei]
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Magpie
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[*] posted on 4-12-2017 at 09:45


You can get full vacuum hose at Carolina Biological.

That's a beautiful pump. What kind is it and what price?

I want a sign like you have.



[Edited on 4-12-2017 by Magpie]




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[*] posted on 4-12-2017 at 10:02


It's a pity that they don't make this stuff a bit bigger bore
https://www.johnlewis.com/john-lewis-curtain-wire-kit-with-h...

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[*] posted on 4-12-2017 at 16:26


I use this braided reinforced vinyl tubing for my pump. I found it at Home Depot for fairly cheap, and it works excellently. No worries about that collapsing.
IMG_4016.JPG - 1.4MB




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weilawei
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[*] posted on 5-12-2017 at 07:21


I bought the sign at a halloween store, but you can order one from Target.

The pump, a 2015 Adixen 2021i, was (brace yourself) $850 rebuilt (before freight) and came with an automatic gas ballast, but did not include any other fittings. I purchased everything else separately. The entire setup, gages, OME, fittings, tubing, oil, cold trap, dewar, dry ice maker and all odds and ends, ran about $1500 total cost. Some people buy fancy new computers... I bought a pump. I work a stupid amount of overtime 60-70 hours a week to afford it.

Thanks for all the suggestions on tubing! I'll check those out.

[Edited on 5-12-2017 by weilawei]
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[*] posted on 5-12-2017 at 07:51


Ouch. Sorry, but that sounds like a ridiculous amount to spend on a pump, and I'm saying that from the perspective of someone who spends an unhealthily large chunk of his income on lab supplies. I bought a used rotovap for much less than that, and use a $30 single-stage rotary vane pump from Amazon with it (boils water off nice and fast at about 55ÂșC). Why do you need such an expensive pump?



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Chemvironment
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[*] posted on 5-12-2017 at 08:08


Does anyone else find the humor in "skimping" on vac hose after dropping $1500 for the set up? Awesome pump in any case. Your next purchase should be some lab jacks. Those books look precarious at best.

[Edited on 5-12-2017 by Chemvironment]
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weilawei
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[*] posted on 5-12-2017 at 08:17


Eventually? To back a GC/MS. How often do we have questions about products produced and purity? All too often for trying to do science as opposed to demonstrations. And hopefully, I can make that available to others.

As to skimping, that was more mistake than skimping. I purchased the wrong wall thickness tubing. My shock at tubing price is the enormous difference in price for the same exact material and manufacturer for a slight difference in thickness.

To each their own. I'd rather buy it once and maintain it and have it last my lifetime. I'm certainly not interested in pumping all sorts of crud through it. That's what a cheap HVAC pump is for or an aspirator.

Why buy a gaming PC (or other effectively disposable item) that will be outdated in a year? To accomplish what? This falls under long-term purchases.

[Edited on 5-12-2017 by weilawei]
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