Sciencemadness Discussion Board

Vacuum Pump

Maui3 - 1-11-2024 at 05:30

Does anyone a recommendation to a place to buy a vacuum pump for vacuum filtration and rotovap?

It's probably cheapest to buy used.

I don't know a lot about vacuum-things, so I might sound very dumb. How do I check, and how strong of a vacuum is usually used for vacuum filtration and rotovaps?

Thank you!

Sir_Gawain - 1-11-2024 at 05:54

I don’t know about rotovap, but for vacuum filtration I would recommend a water aspirator. They’re very cheap, and you don’t have to worry about corrosive chemicals damaging it. I 3d printed one and it pulls a strong vacuum just using water from the tap.

Maui3 - 1-11-2024 at 06:20

Not a bad idea!

Dr.Bob - 1-11-2024 at 06:40

For a rotovap, a simple membrane pump works well or you can try a simple HVAC pump like Northern Tool or Harbor Freight sells. An asirator for a rotovap is going to use a lot of water. But for filtering things, an aspirator is generally OK. Neither needs a supper string vacuum, unless you are trying to rotovap DMF or such.

Maui3 - 1-11-2024 at 08:51

Thank you Dr.Bob I will look more into that.

Sulaiman - 2-11-2024 at 00:15

I do not use my HVAC vacuum pump for filtration because;
. Very low pressures boil water, solvents etc. at room temperatures
. Many filter-vapours can damage the oil or aluminium of the pump
. HVAC pumps are very noisy, not designed for continuous duty and consume a few hundred watts of electrical power.

A small hand pump or a water aspirator seem popular choices for filtration,

I like cheap 12Vdc vacuum pumps because they work well,
run for days with no problems, not too noisy, consume little power,
are cheap enough to be semi-disposable, and I have 12Vdc supplies available.
My -75 kPa pump filters a little quicker than my -65 kPa pump.
(I think / it seems logical that) filtration flow rate is directly proportional to the pressure difference
(until other effects such as boiling occur)

Keras - 2-11-2024 at 06:25

For vacuum filtration I use a cheap Chinese pump (see picture).

I was expecting low quality, but it’s reasonably sturdy and does a good job for the price. Even if it’s given for 12 VDC, I rarely have to push it over 4 V to get good filtration.

I even used it once for vacuum distillation, and I was surprised at how well it worked. It was almost as good as my water aspirator.


IMG_2871.jpeg - 247kB

wells_c - 2-12-2024 at 02:42

I'm a month late (Just joined, and am reading through posts) but I do some composites work, and started out building surfboards for a hobby.

Refrigerator compressors work very well as vacuum pumps, and can be had for free providing your local refuse facility provides for that access. Of course in some areas fridges can be found dumped by the road... the only drawback is that usually the loop is still charged with coolant gas. Try asking an appliance repair, HVAC or auto AC shop if they would drain it for you and properly handle the gas. After that you can extract it from the fridge, hook up the power, and determine the in and out ports. They are oil-submerged, so it may burp oil the first start. Also to make sure there's enough oil, you can carefully feed oil into the intake with the air until the outlet starts spitting out oil. As with all oil pumps, the outlet will produce oil mist, creating a trap is easy enough.

They are very reliable when used correctly, are almost silent, and pull a pretty decent vacuum. I use an inches-mercury gauge (talk about your non-SI unit...) which goes from 0 at atm to -30 (or so) at full vacuum, and my fridge pump would read very close to max. Turning on my newer pump will just make the needle twitch down a touch, not even a whole unit.

Also composites supply places often sell vacuum switches with adjustable set-point, so you can dial in the level you want. You'd need a reservoir and possibly a line restriction to keep cycling time reasonably long; rapid cycling will be bad for the pump. Check for overheating once in a while also.

Hope this is helpful,

W

Mateo_swe - 2-12-2024 at 06:44

I bought a used Vacubrand diafragm pump on ebay.
These pumps are made for chemical use and there are replacement parts avaliable.
They cost quite much new but one can sometimes find used ones on autionsites for a decent price.
These can be used together with a rotovap but you need the rotovap vacuum controller if you want to control the amount of vacuum.
If you do much chemical experiments this might be an option, it will last you a very long time.

But the small pumps like in the picture above is very useful if one only going to do filtrations and low vacuum stuff.
They are so cheap that it doesnt do so much if one breaks, just buy 2 so you have one in backup if the first one breaks.

Deo - 3-12-2024 at 15:48

Quote: Originally posted by Sir_Gawain  
I don’t know about rotovap, but for vacuum filtration I would recommend a water aspirator. They’re very cheap, and you don’t have to worry about corrosive chemicals damaging it. I 3d printed one and it pulls a strong vacuum just using water from the tap.


Could you send the 3D model? I wanna print one as well. Also I was wondering have you measured how powerful the vacuum is?