Sciencemadness Discussion Board

DIY water aspirator vacuum pump

Catslovechemistytoo - 8-9-2024 at 03:34

I've been trying to make an aspirator vacuum pump out of plumbing parts, however it does not pull vacuum even remotely. The best I've got is 80-90kPa, which is even worse than the vacuum I get on commercial aspirator pump like this one which gives 50-70kPa at best. These seem to give poor vacuum for other people as well. Some commercial aspirators can give very good vacuum like 2-10kPa.
Does anyone have a blueprint or a general advice on how to build aspirator pumps?

jackchem2001 - 8-9-2024 at 03:54

How are you determining your level of vacuum?

Catslovechemistytoo - 8-9-2024 at 09:17

Quote: Originally posted by jackchem2001  
How are you determining your level of vacuum?

By using a manometer in vacuum outlet of the aspirator.

Twospoons - 8-9-2024 at 13:31

If you post a drawing of your build we might be able to suggest improvements.
Many things like this are simple in principle, but getting them to really perform well can be tricky, and takes good design and careful construction.

There's a nice cross-section here
I would suggest the biggest performance improvements could be had in the design of the 'diffuser' section. In every commercial design I've seen this is a smoothly tapered section that reduces down to the jet diameter then expands again. I would guess the idea is to get the water flow to attach to the walls in the throat of the diffuser, creating a block to back-flowing air.
Not the easiest thing to make in your garage.

[Edited on 8-9-2024 by Twospoons]

Rainwater - 9-9-2024 at 10:45

Assuming nice and smoth surfaces there is an equation that will tell you the maxium pressure gradient possible with a geometry. Ill do some digging when I get home.
Here are the 3d printer stl files and scad used to generate them. Fully parameterized
Maxium vacuum i get with this is at 6.5L/min @ 75psi around -16inhg
Edit: forgot the link
https://www.sciencemadness.org/whisper/viewthread.php?tid=15...

[Edited on 9-9-2024 by Rainwater]

Sir_Gawain - 9-9-2024 at 14:26

I've printed this one. I haven't tested it yet.

IMG_1208.jpeg - 1.1MB

It's printed in PETG, and smoothed by dunking in DCM.

Sir_Gawain - 9-9-2024 at 17:57

Just tested it, the best vacuum I got was around 20 in Hg.

Precipitates - 9-9-2024 at 17:58

Quote: Originally posted by Catslovechemistytoo  

the vacuum I get on commercial aspirator pump like this one


I find it difficult to attach plastic tubing to this one as well - maybe I'm doing it wrong, but it just kept pinging of at the intake for me, so I ended up attaching it straight to the water faucet. Based on boiling point calculations I achieved about 20 kPa (water boiled at 60°C).

Quote: Originally posted by Sir_Gawain  
I've printed this one. I haven't tested it yet.

It's printed in PETG, and smoothed by dunking in DCM.


Something like this does look better, but I guess wait and see how it performs.

Edit: Was just beaten in my reply :D
Quote: Originally posted by Sir_Gawain  
Just tested it, the best vacuum I got was around 20 in Hg.


That's pretty good! Damn I want a 3D printer.

[Edited on 10-9-2024 by Precipitates]

Sir_Gawain - 9-9-2024 at 19:25

Quote: Originally posted by Precipitates  

That's pretty good! Damn I want a 3D printer.

I just got my first one a few months ago (I actually won it in a contest from the YouTuber Integza). I’ve printed several pieces of lab equipment - funnels, flask stands and the like. I would highly recommend getting one. They’ve gotten a lot cheaper over the last few years.

Catslovechemistytoo - 11-9-2024 at 02:21

Quote: Originally posted by Sir_Gawain  
Just tested it, the best vacuum I got was around 20 in Hg.


Do you mean you measured -20inHg, as in 30kPa? Or you only had 20inHg reduced pressure in total, as in 67kPa? If first, it's pretty good vacuum for a 3d printed part.

I wonder, what if we use something else instead of water to create vacuum? My understanding is that with more viscous liquid (and with cooler liquid too) there should be stronger vacuum. Maybe water-glycerine mix cooled with ice is better than just water?

jackchem2001 - 11-9-2024 at 17:28

The vacuum is limited by the vapor pressure of the fluid, so a low vapor pressure oil would be ideal. However, everything you pull a vacuum on will end up in your oil, so this really defeats the point of a water aspirator in my opinion. You may as well just buy a vacuum pump at that point

Twospoons - 11-9-2024 at 17:58

Well, the low-hanging fruit there is to use a saturated brine instead of water, in a closed loop aspirator vac pump. It should get the pressure a bit lower, and is cheap enough to dispose of if it gets contaminated. You could then chill that to -18C in a domestic freezer.

But as said, its getting to the point you might as well invest in a mechanical vacuum pump.

[Edited on 12-9-2024 by Twospoons]

Sir_Gawain - 16-9-2024 at 12:15

If anyone (in the US) wants an aspirator pump, I’d be happy to print a few and mail them out.

jackchem2001 - 22-11-2024 at 23:16

Is it worth buying an accumulator tank? I'm thinking about doing my first vacuum distillation but am worried about pressure fluctuations causing bumping

Sulaiman - 23-11-2024 at 01:05

One method of obtaining constant water pressure is to use a header tank,
I used plastic tubing to siphon water from the tank/cistern of an upstairs toilet.

................................................
I often used an aluminium water bottle between my equipment and mechanical vacuum pumps.
It smooths out the pressure pulses
It catches any liquids,
It can catch dust if filled with oily steel wool

It can also be used as a silencer/muffler and/or mist trap on the output side of a mechanical vacuum pump