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Author: Subject: homebrew aspirator
Tacho
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[*] posted on 17-9-2004 at 16:13


Centimeter,
Considering what I have learned so far, I believe it’s possible that you can built an aspirator that gets 200 torr out of your pump. However, I don't think it will be easy, and you will have to test designs and that takes time, money and patience. I would start with the model described in frogfot's page to see how it behaves. With some fine tuning, like trying different distances from nozzle to throat, you may get a useful vacuum.

I see neutrino has already answered about the pressure calculations, but I had written this text and will post it anyway:

Volume has nothing to do with it. If your aspirator pulled water 7ft high, it could have pulled mercury 157mm high. Since atmospheric pressure is about 760mmHg, your vacuum was 760-157=603mmHg. That’s about… hummm… 603 torr.

By the way everybody: The one-way sphere valve I described, using a mouse ball, is excellent. Much better than my previous small steel sphere one. It has been holding a 300 torr vacuum in a PVC setup that has over 3 liters for over an hour! The only hard-to-find piece is the rubber o-ring, but it may work without it, since the ball seems to be covered with rubber anyway.
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HRH_Prince_Charles
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[*] posted on 18-9-2004 at 06:06
Achievable Pressure


The thing that governs the limiting pressure of the water-jet pump is the velocity of the water jet.

15 m/s gives a negative pressure of around 1000 mbar.

The problem with your water pump,cm, is that it doesn't have enough pressure to give a high speed jet. You'll get some pressure reduction, but not much.




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Tacho
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[*] posted on 30-9-2004 at 15:31
A vacuumstat.


I stripped my old vacuum gauge and connected the bourdon tube to a microswitch, using a brass lever. Now I can automatically keep my vaccum in a given range. The maximum is adjusted turning the screw. I adjusted it to to turn off the pump at 140 Torr and it turns it back on when vacuum falls to 220 Torr.

Works marvelously (sp?).

Note: the switch I used was in my scrapbox and is turned off when pressed, not when released.


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Mendeleev
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[*] posted on 30-9-2004 at 15:37


What is the general sucking capacity of a typical aspirator? I realize the vacuum strength is just a little over the vapor pressure of whatever liquid you are pumping through it, but how about capacity? Could an aspirator evacuate a 2 L container? I ask because mine pulled a 733 mm vacuum when connected directly to the pressure gauge running water from the tap, but when I hooked it up to a 1L flask equiped with pressure gauge it managed to do about 620, with a brief spike to 700. What's the problem?



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Tacho
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[*] posted on 1-10-2004 at 03:08


Bottomline:
If you have a one-way-valve, try turning the pump off than on again.

Making a short story long:
When I turn on my vacuum station, pressure goes down to about 560mm (my vacuum gauge reads like yours) and stops there. I turn off the pump manually and wait until all water "falls" from the aspirators (glob-glob-glurrp sound). The ball-one-way-valve holds the vacuum (the white cilinder at the right of my last picture). When I turn the pump back on, vacuum goes quickly to 620, where the vacuumstat turns it off automatically.

I don't know why this happens, hydrodynamics is extremely complex! :D*lol*

The rest of the information you seek can be found in other posts in this thread.

Wish you luck.
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HRH_Prince_Charles
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[*] posted on 1-10-2004 at 15:27
Typical Aspirator


Mendeleev:

The typical pumping speed of a lab. water-jet pump is 67 ml/s or 0.15 cfm.

The pressure falls exponentially. To evacuate a 2L flask down to 20 mbar from atmospheric will take 5 minutes or so.

You either have some instability in your pump or a leak - possibly the latter.




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Mendeleev
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[*] posted on 2-10-2004 at 10:04


There were no leaks in the aspirator itself because it is a very nice glass aspirator I bought for $9 from an ebay store. I am guessing, I just had crappy hose connections, because when I set up the apparatus again, it managed to pull 700 mm consistently from a 1 L flask, but would not go 1 mm more despite running for 3 minutes. I am fairly pleased with 700 mm Hg vacuum, but where did those other 33 mm go?



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[*] posted on 2-10-2004 at 11:09
Ultimate Pressure


How good is your vacuum gauge?

Another way to measure the pressure is to evacuate a small flask with some water in and see at what temperature the water boils.

Are you running the aspirator from a tap or a pump?




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Mendeleev
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[*] posted on 2-10-2004 at 15:46


My pressure gauge is pretty good, and I am running cold tap water, I was thinking of getting a bilge pump and pumping ethylene glycol through it, but I don't know if a bilge pump could handle it, I think ethylene glycol is a lot more viscous.



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[*] posted on 3-10-2004 at 06:49


Someone should try running steam through their (homebuilt, maybe) aspirator, and see what can be achieved. I did a highschool science fair project a couple of years back that was a design for a solar powered air conditioner, it used solar-generated steam to power a steam ejector, making a vacuum that made water evaporate faster, absorbing heat. I discovered that it wasn't practical, BTW, but at least the idea got me to nationals.

A steam ejector is like a aspirator, except that it is powered by a jet of steam instead of water. The theoretical pressure limit is lower, because, like in a diffusion pump, the vapor is jetted out fast enough that it doesn't escape into the vacuum line for the most part.

I wish I still had the one I used, it was quite a design. Solid titanium, it was a rectangular block that had been drilled out to shape, very precise. Unfortunately, I had to give it back to my brother, he had got it via Honeywell, who he used to do design work for (sensors for pulp&paper mills).

Edited for spelling

[Edited on 3-10-2004 by Oxydro]
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Tacho
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[*] posted on 3-10-2004 at 14:06


Sorry Mendeleev, I did not read your post carefully. I realize now you are working with tap water, so my sugestion makes no sense.

The probable reason for the problem I described above is the air bubbles that get trapped in the water that circulates in a pumping station. A larger baffle may solve that problem.
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[*] posted on 13-10-2005 at 12:57


A bit of information for future vacuum station builders: I tried to use a dishwasher pump and the results were lousy. Only 550mmHg with very small pumping speed.

I don't know the exact power of the pump, but it seems pretty heavy duty and I estimate about 100W.

That's a shame, because the whole station was very light and portable.
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[*] posted on 13-10-2005 at 15:48


If the pump had a shaded pole motor (very likely) then I'm not surprised. The ones we used on clothes washers pulled 90W electrical, but only put out about 8W hydraulic. Appalling efficiency, but they were dirt cheap.



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[*] posted on 10-9-2006 at 16:23
Sump pump


sorry to dig up this old thread, but I have been working on a "water aspirator pumping station."

I made the aspirator by using frogfot and tacho's method. I am using an old rusty sump pump, the kind that pumps water out of your basement to prevent flooding or damage to the structure. It is pretty powerful, but I am not sure if these things are designed for continuous operation. Is it ok to have one of these running continuously for an hour or so, while I do distillation?

Another thing is should I be worried about overheating, the pump will be about half way in the water (heat sink) but have noticed it being hot to the touch even then.

thanks.

Mericad
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[*] posted on 11-9-2006 at 15:29


Anything robust enough to pump out your basement should be robust enough to run for an hour or so. I don't know the exact cooling mechanism of your bilge pump, but the ones I have seen can draw water down to a depth of less than an inch and don't need to be fully submerged.

Remember, the power needed for a typical water-jet pump is low - less than 100 W. You need a head of say 15 m and a pumping speed of say 15 L/min. If the pump is too powerful, you will dump too much heat into the water and [edit] raise the limiting pressure of the water-jet pump.

[Edited on 11-9-2006 by Mr_Benito_Mussolini]
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[*] posted on 12-9-2006 at 03:36


Basically what you are asking is "will my X pump handle it?". I don't think anyone can answer that.

But what the Duce posts is true. You don't need much power to make the typical water-jet pump work. Maybe you should consider a by-pass to release some pressure and not stress the pump. Or use more than one aspirator in parallel.




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[*] posted on 2-2-2012 at 23:01
sorry to reawaken an ancheint thread


... however I once made one


I took a little plastic hose adapter, then flattened the edge while heating it.

I cut off one arm of a t connector, then shoved it in as hard as i could and tightly wrapped it in parafilm.

It worked alright. i think what's important is that the water entrance and exit are about the same size. I don't think the vac part has to touch the water, just be in a sealed chamber with entrance and exit for water being roughly equal.




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[*] posted on 16-7-2012 at 04:23
yet another aspirator


Thanks almost exclusively to info in this thread, I also made one yesterday.
mv_aspirator_plan.jpg - 112kB mv_aspirator_photo.jpg - 37kB

Notes:
Brass tubing, copper tubing + drilled endcaps, all metal connections soldered (Ag/Sn). The 4mm OD orifice was centered inside the 5mm ID tube with a bit of thin copper wire, then soldered. Orifice/exhaust ID ratio is 0.6 exactly. The conical jet receiver is made of FIMO clay (the type that you bake in a kitchen oven to harden). The bottom endcap was not pushed all the way onto the copper tubing, so that the clay can grab it better. A standard garden hose (not shown) fits over the top part and gets clamped with a nylon tie or some wire, just below the endcap. Clear PVC hose at exit end made all the difference: not even 500mbar without that.

Performance:
Feels very sturdy. Took some 30 seconds of pumping a 320ml jar until my cheapo vacuum gauge landed all the way down at zero. A spoon of water in the jar started bubbling after heating the jar bottom with my hand. 50mbar?

Thank you all for the key points! This one will be used for flash pickling of food. Yummy. :)


[Edited on 16-7-2012 by matjazv]
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