smaerd
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Vacuum Valves?
So I don't necessarily mind that their 3 dollars a piece but avogadros has some pretty bad shipping costs. http://www.avogadro-lab-supply.com/item.php?item_id=1292&...
I have heard most ball valves will hold a vacuum but again locally those are probably around the 5-6 dollars a piece at hard-ware stores and kind of
heavy, as well as not designed for vacuum use/lab-use.
Anyone know of a web-site with cheap stop-cocks for general vacuum use(nothing fancy just using a fridge pump) and maybe a few other lab
accessories(rubber stoppers etc)? It's hard to imagine there's only one place with these little things.
Tried using the search engine and checking the usual suppliers and couldn't find much of anything. If this is a dead-weight thread feel free to remove
it  .
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smuv
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I think ball and gate valves available from hardware stores should be fine for this type of vacuum work. Maybe grease the valve seat with plumbers
grease (which is essentially the same stuff as vacuum grease, just a touch waxier in consistency).
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aonomus
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http://www.usplastic.com/catalog/item.aspx?itemid=23912&...
No barbs, but cheap.
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smaerd
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Thanks for the link I'm going to try them out
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Contrabasso
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If you are doing reduced pressure distillation look at the local pet shop and get fish tank airline parts, T pieces and plastic needle valves. Limited
in bore function and price, depends on your needs and point of view.
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garage chemist
chemical wizard
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These plastic valves are so cheap and shitty. I once used one as the bath drain valve on my cryostat and it kept leaking alcohol.
I am sure they mean nothing but trouble if you are trying to use them as vacuum valves. Don't buy this plastic crap.
The other day, I purchased a glass/PTFE valve from my glassblower, and had a talk with him about vacuum valves in general. He informed me in detail
how the different qualities of glass/PTFE valves are constructed, and which ones are worth their money.
The PRODURAN valves from Schott are unique because they have four internal gasket rings that press the thin PTFE jacket against the glass to guarantee
air-tightness of the stopcock, and the pressure of these gasket rings against the glass can be re-adjusted by a screw when the PTFE jacket wears down
a bit over the years.
These are the most reliable PTFE vacuum valves available, and the only ones that are really worth their money:
http://www.duran-group.com/en/products-solutions/glassware-f...
The smallest one is about EUR 50 from online shops, but glassblowers can get it for less.
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smaerd
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I really only plan on using them for vacuum filtration, vacuum assisted chromatography, and maybe basic vacuum distillations(fridge pump won't seem to
do vacuum frac. distillation?).
Garage chemist as much as I'd love to blow 60 dollars on one valve when I want two of them, I have 15 dollars in my bank account. With 120 bucks(even
higher in the USD) I could invest in a lot more interesting and more immediately gratifying things hehe. One day though. It's kind of hard to believe
that a valve designed to move water would leak liquid? That's a real shame.
So do the aquarium valves hold vacuum decently? Should I be looking into ball or needle valves? Are plastic ones okay?
Edit - maybe something like this - http://www.aquacave.com/detail.aspx?ID=2314#Reviews
[Edited on 5-4-2011 by smaerd]
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smaerd
International Hazard
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So I went against the grain here and ordered a couple valves from the USplastics website, they were cheap and I needed some reducing adapters anyways.
Plugged it in line into my fridge pump, put my finger on it with the valve open, it sucked just fine(no meter to gauge), then tried closing the valve
for a second or two, then when I opened it WOOOSH, it sucked air in. So it holds a vacuum perfectly fine for the needs I'll use it for. Thanks for all
the advice.
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Contrabasso
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If you want to hold the vacuum from pump and diffusion pump then fish tank bits are clearly not up to standard, BUT if you want to control a minor
reduced pressure the fish tank bits can be suitable and in budget!
You have to chose the equipment that you use carefully especially when budgets are small.
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IrC
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Forget fish tank valves. Go to a place with swamp cooler parts and get the similar needle valves in brass for cheap
(under 3 bucks each). Used to turn the water lines on/off. I have already found they will hold vacuum for years. My little Bell Jar setup uses them
and it was still above 29" after 4 years of storage. Meaning they do not leak at all, plus you can then use copper tubing and compression fittings,
the other secret to holding vacuum for years.
"Science is the belief in the ignorance of the experts" Richard Feynman
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smaerd
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Awesome recommendation I'll probably do that in the future. I'm doing a mason jar set up as well . Sorry to continue bumping this.
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chemrox
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I'd be really wary of that plastic shit and I would definitely not use hardware store stuff. I used a Nalgene stopcock on a T as a relief valve and
still pulled 0.1 T with a decent 2 stage pump. I changed the system around to a manifold and trap and it pulls a lot more. I also use an aspirator
pump because my tap water gets up to 50C in the summer. I throw ice in it when I'm running the evaporator. If you're using an aspirator you should
try to get as much out of it as you can. Seal around all the connections and strap or wire down your hoses.
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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