Jor - 5-4-2009 at 03:30
I have been looking around for a cheap vaccuum source, because it makes filtering so much easier. I don't need vaccuum for any other reason, such as
distilling or evacuating a dessicator, just filtering.
Now by far the easiest way to go is buy an aspirator, wich can be connected to a tap. However, no tubing or aspirator fits on my tap. Woelen also has
explained me how to remove some parts, such that it can fit, but I cannot remove anything for some reason from this tap.
Because i do not want to install a new one and waste much time on it, i have been looking for an alternative. I have found at my supplier a hand
operated vaccuum pump. He sells it for 45 EUR, and imports it from USA. I went to look for on in the USA, and found out crscienctific sells one for 30
dollars, much less.
My question is, does anyone have experience with these?
http://www.crscientific.com/vacuumpumps.html
Is it possible to quickly filter something with this, and suck the solid dry?
Also is crscientific a reputable supplier? It seems so, but experience is better than my feeling.
indigofuzzy - 5-4-2009 at 16:06
I have a vacuum pump just like that. It broke (the first time) after a week or so. (The plastic piston cracked.) I screwed a metal disc in to
reinforce the piston, which got it working again for about 2 more weeks before the joint between the piston and the handle broke off. I drilled holes
in it, and tied it back together with steel wire. It hasn't broken a third time (knock on wood).
Anyway, If you get a plastic hand pump, either be super-gentle with it, or expect it to break.
I suspect that an aspirator will give you better vacuum. Mine can pull enough vacuum to make hot tap water boil, but not lukewarm. The gauge will read
roughly 660mmHg below ambient under ideal conditions. But if I try to pump down a 750ml glass bottle, I can only get 600mmHg below ambient.
indigofuzzy - 5-4-2009 at 16:10
OH, one more thing, the gauge on mine was miscalibrated, so it reads ambient as -100mmHg. When I quote -660mmHg, the gauge is actually reading
-760
Vacuum
MadHatter - 5-4-2009 at 18:36
You do have to be gentle with one of those hand held pumps. I bought one at an auto
parts shop. As for aspirators, I love them ! 
I found that a combination of
parts from a
hardware store works. Just be sure the last piece to connect to the tubing has a
barbed end on it. My combination screws into the faucet and has the same threading as the
aerator. Also use small tubing clamps, to hold the tubing on. Tighten the clamp gently
on the aspirator if it's made of anything except metal.
Magpie - 5-4-2009 at 19:34
I agree that aspirators are very nice for vacuum filtrations. I also use mine for vacuum distillation.
I don't know what you are up against with the spigot you now have, but I recommend you give woelen's suggestion a good try. Here's where I post a
picture of an adapter I made for my kitchen spigot:
http://www.sciencemadness.org/talk/viewthread.php?tid=8352#p...
I can vouch for CR Scientific as being a very good supplier.
chemrox - 5-4-2009 at 21:16
Nice job Magpie. I have an all glass aspirator in my drawer that would be easy to adapt with flexible hose.
procrastinator - 4-5-2009 at 09:17
If you want a really cheap, hand-operated low vacuum pump, you can easily make one yourself. All you need is:
--A large syringe. The bigger it is, the more air you can pump out in one stroke. I recommend at least 50mL
--Two one-way valves, a.k.a. check valves. The lower the cracking pressure, the stronger the vacuum you can ultimately pull
--A T-adapter
--Some rubber tubing to hold it all together. I personally recommend silicone tubing. It's nearly transparent, seals well, and is resistant to almost
everything.
You connect them as follows: Syringe -- T-adapter -- (Check valve)2
One valve will let air in to the T-adapter (connect this to your filter flask), the other will let air out.
Just pump the piston on the syringe in and out. The valves will take care of the flow control. As an added bonus, let the plunger on the syringe go
after drawing air in and you'll get a rough measure of the vacuum. At maximum vacuum, releasing the plunger on mine lets it slide from 60cc to 10cc,
meaning I have ~1/6 atm.
I know they have one-piece valves that do all this, but I have yet to find one.
Jor - 29-12-2010 at 08:02
I had to bump this. I really get annoyed by not having vaccuum for filtrations. Sometimes decanting is impossible, and gravity filtration is simply
too slow. An aspirator is not practical in my case.
So I decided that i will have to buy a vacuum pump when I have the money. However, I read about a improvised solution of creating a vacuum.
What if I put a Buchner on a side-neck filter flask, and connect the tubing to a gas-inlet glas piece, mounted on top of a large seperatory funnel
filled completely with water. Now if I pour liquid (together with some precitipate) on the filter, and open the seperatory funnel, will the filtrate
be pulled through the filter? Also if there is a large amount of solid there?
I cannot try this, as I don't have a Bucher and side-neck flask. Can anyone try this for me, as this would be a cheap easy substitute for me.
blogfast25 - 29-12-2010 at 08:10
What precisely do you guys mean by 'aspirators'? Vacuum cleaners? A water flow based suction 'pump'?
[Edited on 29-12-2010 by blogfast25]
User - 29-12-2010 at 10:20
Wateraspirator ?
One of those things you screw on a tap and generate vacuum ?
http://www.sigmaaldrich.com/prodimages/g/g007631.jpg
Or is this too obvious.
[Edited on 29-12-2010 by User]