Testing of small dc pumps for vacuum filtration

This is how I would proceed (brainstorming)

the main idea is to check:
1) how good was the filtering ( filter/filtration effectiveness by turbidity or by drying)
2) how long it takes (by volume)
3) how the other two relates to different substances.

Procedure:

1)if not graduated, adding a centimeter to the funel.
2)if not graduated, adding a centimeter to the receiving flask. (maybe not needed)
3) making a makeshift "turbid/color-imeter" with a flashlight, black box, and cellphone(+ any colorimeter/photometer app that could be used)
(attached a picture of what I meant)
4) using an excelsheet:
starting conditions:
substance:
weight:
volumen:
Note: (for example: it was stirred for 10 seconds)
a-timestamp
b-starting funel/ending funel meassure. If you want to only answer: "how much time takes for X ml), this is not necesary, but if you want a graph of filtering against time (because of clogging) this information is needed.
c- receiving flask meassure. (maybe not needed)
d- starting turbidity of sample (using the meter)
e- turbidity of the filtered solution. (once finished, it should be stirred, because of decantation. (filter/filtration effectiveness)

another test, is to take the filtered solution, and redo the experiment (without cleanning the filter), to check how good is to make a second filtration (this is used often in chemistry, so I think is good to know) or maybe a third.

(also if you have time, you could remove water by boiling and check weight of the substance against the starting condition (measssures with more presicion the filter/filtration effectiveness)

and will try different reagents (CaSO4 should be used, because is found a lot in chemistry).
Water should be your first reagent as to have a known standard, and compare the rest to water.
You should try a reagent that settles fast, maybe a lead salt, an a reagent that makes a colloid.
You could make a solution and let it stand (decantation) and more or less check how it clears in a graduated cylinder.

if you want to go pro (or maybe take some ideas):

https://assets.thermofisher.com/TFS-Assets/LPD/Application-N...

ASTM D7315-17
Standard Test Method for Determination of Turbidity Above 1 Turbidity Unit (TU) in Static Mode
https://store.astm.org/d7315-17.html

If you proceed, please post your results.

Quote: Originally posted by AvBaeyer

...How about a slurry of diatomaceous earth (filter aid). Filtering such a mixture is a common lab procedure...

@MrDoctor: why do you want to make my life difficult ?
calcium sulphate aka gypsum plaster is one of my least favourite things to filter.
(my least favourite is hot saturated solutions of anything)

I have two banks of three peristaltic pumps ex-dairy
after replacing the silicone tubing each one got to -1atm on a cheap Bourdon gauge,
maybe a tiny bit more pressure than my dual-stage rotary.
very very very slow pumping down though.
https://youtu.be/gGtYlS1ihbE?si=fSSyno99yzMYdBap
___________________________________________
@AvBaeyer: thanks for the diatomaceous earth vs frit tip.
____________________________________________
My new vacuum pump arrived yesterday - with a crack in its plastic body.
I've claimed refund already but this will delay these experiments.

Quote: Originally posted by MrDoctor

my point was that it IS unpleasant to filter, and its a contaminant that can occasionally pop up unexpectedly. Also AvBaeyer, filtering the copper sulfate without the insoluble hard-water precipitate renders it meaningless. something as innocent as trying to recrystalize copper sulfate accidentally using tap water, can render it unfilterable, which is especially problematic given you want to filter it quickly while its hot, that first time.

isn't it amazing how something as seemingly simple as filtering stuff
is not simple at all.
Like everything, the more you learn the more you realise you know very little
__________________________
I may try CuSO₄ with added calcium ions,
it is a good representative test,
I could filter a cloudy suspension to transparent blue/green - nice.
but not hot and saturated

for sale at the moment

Because the new dc motor vacuum pump that I ordered arrived broken
I got a refund and looked again for "dc motor vacuum pump"
Just out of curiosity I looked for the cheapest:
For free postage (and spares) I ordered 3 for equiv.USD4 total



just arrived and tested .....

better than -60kPa at 3.7V 330mA

a USD1.33 pump, some tubing plus a lithium cell and you're ready to go.
more than enough for vacuum filtration - I expect ......tbd

[Edited on 21-8-2025 by Sulaiman]

i have those exact ones, they are nifty little suckers. i have always wondered if there wasnt some sort of counter-solvent i could introduce so those rubber diaphragm pumps would stay safe. like say, via a submerged bleeder valve introducing water, or vegetable oil or something like that, so it always sputters out a bit and hopefully causes any absorbed solvent to diffuse onto the bleeder-solvent keeping the rubber relatively pure and safe. ive seen this implemented for peri pumps but moreso because i think they work better with a little something to actually pump so the hose isnt just fully collapsed under vacuum, or being slick with a lubricant just helps i guess.

If anyone should choose to make the compromise on one of those big cheap plastic open piston-pumps, something important to keep in mind is they dont use any sort, i guess cam-bearing? basically that pison is directly hanging on an unlubricated metal rod with no bearing or bushing, and 3 minutes under load melts that rod right out.



even if you submerge it in lubricant, which is a merit to the design, it will still melt without a strict, low duty cycle. whatever the intended application is, it is weirdly common, or at least was at some time, so be cautious about that, just because it uses a replaceable O-ring as a piston seal and can be lubricated under oil to control wearing and sealing. big waste of money.

[Edited on 21-8-2025 by MrDoctor]

Quote: Originally posted by bnull

@MrDoctor: Please scale down the picture.

Right, I forgot that HTML is off and [img] has no size option.

Edit: Some sites store images in different sizes. The one above has a 640x640 available (https://cdn11.bigcommerce.com/s-g34rj6mm5p/images/stencil/64...)


This is one workaround that occasionally works. The other is resizing the picture in a phone or computer application.

[Edited on 22-8-2025 by bnull]

just testing

I just downloaded the photo, cropped it a tiny bit and uploaded it.
The differences must be in our OS and/or browser

[Edited on 22-8-2025 by Sulaiman]

Quote: Originally posted by bnull

About @MrDoctor's no-bushing plastic piston pump, one can repurpose a sleeve bushing from another motor. It shouldn't be hard to find an appropriate bushing and widen the piston shaft hole to fit it.

ten years ago I thought so https://www.sciencemadness.org/talk/viewthread.php?tid=62587
I still have one pump with a melted bearing
my other one still runs but it is very noisy and it struggles to pull -70kPa now.
it is ok for filtration but the noise and vibration is too much for me,

possibly repairable but not worth the effort

the orange/brown is due to my melting the ends back together with a soldering iron - a poor choice
I kept it as spares for the working pump
but soon both of the pump sections will be in the garbage bin
and I will add the two motors to my collection of very useful but never actually used motors

[Edited on 23-8-2025 by Sulaiman]