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Mark Van Adium
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How much vacuum can an aspirator pull?
Theroetically they can pull down to the vapour pressure of the liquid, but I find it hard to believe I can pull down to less than 10mmhg with a vacuum
aspirator and some <10*C water.
How much can they actually manage with water?
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blogfast25
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Sounds like a question for google, really...
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bahamuth
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Remember I found a old old physics kit at work, like the stuff one used at school 20 years ago, which had a chrome/nickel coated brass aspirator which
was stated to produce down to 15mmHg with tap water..
Tested one type, Brand (Plastibrand) plastic aspirator with a electronic vacumeter, and IIRC it gave around 150 mmHg at full juice of the tap. (do not
qoute me on that value, might be way off).
Any sufficiently advanced technology is indistinguishable from magic.
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Magpie
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I get 50-60mmHg with cold tap water using a chrome plated brass aspirator.
The single most important condition for a successful synthesis is good mixing - Nicodem
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blogfast25
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Any pics at all? I've been in the market for one of those or been tempted to get injured in the process of cobbling one together.
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Magpie
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Here's my aspirator as installed. The brass fittings are adaptors from a hardware store. The valve/hose attatchment at the suction port is something
I added to facilitate vacuum breaking and attaching a vacuum hose (Buchner filtrations, etc). Only the steel looking item is the actual aspirator.
IIRC it cost around $20.
The single most important condition for a successful synthesis is good mixing - Nicodem
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Mark Van Adium
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Well damn, thanks guys, digging on google revealed claims from 28inhg to the theoretical limit. I think I'll be picking up one of these!
Edit, do they have any other names, I'm really struggling to find them in britain.
[Edited on 12-8-2011 by Mark Van Adium]
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blogfast25
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Very nice, Magpie.
I second Mark Van Adam: the core of the aspirator may be harder to find here in Old Blighty...
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Magpie
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Here's the one I bought:
http://www.carolina.com/product/filter+pump+or+aspirator.do?...
I also bought a plastic one for $11 but have never used it. It's a NALGENE Vacuum Pump, cat no. 6140-0010. The product info lists a telephone number
in Brussels, so perhaps you can find it in Old Blighty. 
http://www.carolina.com/product/vacuum+filter+pump%2C+nalgen...
[Edited on 12-8-2011 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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Mark Van Adium
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Here's the one I found, I'm looking forward to converting that NPT thread to BSP. Oh for international standards.
[Edited on 12-8-2011 by Mark Van Adium]
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Magpie
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That looks like the same one I have.
Humbolt is a good lab supply company. Their equipment is heavy-duty, professional grade. I have a ring and ringstand, as well as a Meker burner,
made by Humbolt.
The single most important condition for a successful synthesis is good mixing - Nicodem
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blogfast25
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Decent price too!
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Phthalic Acid
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Mark Van Adium, they are called water aspirators, hydro aspirators and eductor jets pumps. You cam buy them on eBay from Avagadro Lab Supply for about
$28USD. Hope this helps you out =)
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blogfast25
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Quote: Originally posted by Phthalic Acid  | | Mark Van Adium, they are called water aspirators, hydro aspirators and eductor jets pumps. You cam buy them on eBay from Avagadro Lab Supply for about
$28USD. Hope this helps you out =) |
...plus, erm... shipping  . Many US eBayers want silly money for getting the
stuff across the pond. And unless it's listed in international listings I don't think we can buy it here anyway. Not w/o going round eBay's back.
[Edited on 13-8-2011 by blogfast25]
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Mark Van Adium
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Yeah, ebay looks to be very expensive, but this place seems fairly reasonable considering I can only find one place with them in the UK, and it's the same price for a plastic one.
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Arthur Dent
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Wow. Thanks Magpie! I'll investigate that place of yours because right now, i'm stuck with a cheap plastic aspirator and it doesn't seem to pull much
vacuum, even at max cold water output... and worse, I paid for my plastic thingie what you paid for your metal one! 
Robert
--- Art is making something out of nothing and selling it. - Frank Zappa ---
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peach
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The theoretical maximum vacuum an aspirator can pull is the vapour pressure of the water when it boils at that temperature. If you imagine the
aspirator is a rearranged kettle, and it's boiling away, the water in it is not going to pull any vacuum because it's happily boiling away at
atmospheric pressure. Practical aspirators lag slightly behind the theoretical maximum.
Another way to imagine it is to think about it practically. The water is exposed to the vacuum it's creating. As the pressure drops around it, it will
try to boil, spraying gas back into the vacuum it's trying to create. The two balance out, so this is the limit of the difference it can keep up
between the two.
At 25C, that maximum will be.... 32 mbar (atmospheric is a bit over a 1000).
That is 24 torr, so 24 mmHg (1 atm = 760), 0.46psi (counting down from atmospheric, 14.5) and finally, 3200 pascals, with 1 atm being 101, 325
pascals.
If you are a young scientist, you should be going for Pascals, as they are SI units and so the most constant and scientifically worthwhile.
Torrs and mmHg persist in chemistry due to the noble nature of mercury and the few points at which a mercury gauge can go wrong. However, the mercury
is not a favourite even in those laboratories due to the toxicity.
If you cool the water, it's boiling point will drop and so the pressure it can achieve will drop until it reaches the limit of what's called the
knudsen flow domain. This is when gases stop being 'sticky' and suckable, and instead enter 'molecular flow', when they are no longer behaving like a
loose solid but rather as a individual molecules. In this region, at ^-4mBar, rotaries also begin to cut out and a different concept is required to
'knock' the molecules through the pump.
32mbar means that over 96% of the atmosphere has been removed, so for filtration, the vast majority of the pressure is already on.
It is also good, even excessive, for removing volatile solvents.
It is helpful / poor for distilling high boilers, like oils boiling over 250C at 1atm. High boilers really need a rotary pump, even if it's a window
AC compressor. For extremely sensitive work, it needs to be a dual stage, involve dry ice and liquid nitrogen and be well maintained; other issues at
this stage include baking the glassware, sodium, molecular sieve and hydride drying.
The aspirator region of pressure is the same achieved by a piston style fridge compressor, down to 10mbar.
| Quote: Originally posted by blogfast25 | | Quote: Originally posted by Phthalic Acid | | Mark Van Adium, they are called water aspirators, hydro aspirators and eductor jets pumps. You cam buy them on eBay from Avagadro Lab Supply for about
$28USD. Hope this helps you out =) |
...plus, erm... shipping . Many US eBayers want silly money for getting the
stuff across the pond. And unless it's listed in international listings I don't think we can buy it here anyway. Not w/o going round eBay's back.
[Edited on 13-8-2011 by blogfast25] |
Boooom, he hits.
Yep.
Since USPS have dropped their 6-8 week shipping, I have lost interest in many items from the US as the flat rate is usually about $36 for any item, no
matter how light (unless it's paper).
That is absolutely stupid.
But it's not the US guys themselves, it's the export mechanisms they're forced to use.
The US, and UK, and everyone, is struggling with money at the moment. I want to give some money to the US, but spending four times as much as the item
on the postage is not part of the plan. Some US guys also have major issues with shipping things out of the US; when they'll actually MAKE money for
the US by doing so.
The same works in reverse. Our VAT system is fairly monged up and it's darn annoying trying to get her majesty's special boys to support small
exports. I have had numerous arguments with them over strange loophole issues in the system, and it's getting quite fun now. I was getting ready to
take HM C&E (the Queens boarder patrol, for the none UK guys) to court over £9 recently (about $10-15). Not for the money or because I don't like
them (I love the post), but simply because the reason for the £9 is malevolent and private exploitation by a member of the public; the owners of the
Royal Mail. I won that arguement. In that they gave me my post when I demanded it from them; only paying the tax and not the surcharge.
[Edited on 16-8-2011 by peach]
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Argyros
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I'm trying to get hold of an aspirator and the only ones I can find are on eBay (US) and the shipping is more then the aspirator.
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Magpie
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You're not giving us much to work with.
http://www.carolina.com/science-lab-filtration/filter-pump-o...
The single most important condition for a successful synthesis is good mixing - Nicodem
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Argyros
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That is what I'm looking for. But I need to find a seller in EU/UK.
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Fyndium
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I have a garden pump that can supply 3.6bar of pressure and 50L/min of flow. I was wondering if I could save a lot of water by circulating a reservoir
with this pump through an aspirator? Now that it's winter, it's easy to cool the water down to 0-10C and keep it there.
Is 3.6bar enough to get full benefit of an aspirator?
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zed
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Yes, you could save a lot of water. Once upon a time, I lived where water was practically free. Well, it isn't free where I live now. It costs
plenty.
Your water pressure sounds.... Well, OK. Flow rate is equally important. And colder water, is better water.
The aspirator itself is usually pretty effective and inexpensive. You will just have to try it and see how it works.
If you aren't in the US, and you need a pump, you might find one in China. Deschem is offering one, in what looks like Brass. That might be helpful
if you chose to make "hard" connections. Threads are not universal, and I had trouble hooking up a Stainless Steel model. Brass, should you decide
to thread a connection, will be amenable to machining..
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Fyndium
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I actually possess an aspirator which originates from German firm Carl-Roth. It's plastic, but from mains water pressure it seems to be getting decent
vacuum. I haven't used it in years though, so I have to test and calibrate it's effectiveness against my vac pump.
At my summer place I could use lake water with the pump. It's rated 600W so technically it would cost about 6c per hour to run it.
Deschem is my go-to supplier. Been ordering dozens of times from them. I remember seeing a brass-made aspirator from them. There was also a stainless
steel version somewhere.
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Fery
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I have 2-stage oil rotary vacuum pump and one old plastic water aspirator pump.
Few months ago I've bought these 2 glass water vacuum aspirators which cost 4 EUR and 10 EUR including VAT:
https://sklep-chemland.pl/en/filtr-wodny.html
https://sklep-chemland.pl/en/pompka-wodna-prozniowa-alvergna...
They will be useful when producing fuming nitric acid sometimes in future.
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Fyndium
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Are glass aspirators better in some aspect compared to steel, brass, plastic, etc?
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