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Author: Subject: Problems getting a decent vacuum from aspirator station
querjek
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[*] posted on 2-7-2009 at 12:38
Problems getting a decent vacuum from aspirator station


Hey there,
I'd had an aspirator hooked up to my sink in the past for light vacuum applications, like filtering. Recently, I realized that I'd like to waste less water, and that I'd like to be able to attempt some easy vacuum distillations.

Attached is a picture of what I've built for this.

The pump, in a plastic container with ice, sends water through the aspirator. When I connected my manometer to this (with a distillation rig on the other end), I can only get a vacuum of -300mmHg, and I believe I should be able to get more, with the 1/2 HP pump I have.

Does anyone have any suggestions for this?

Instead of using multiple, jointed, silicone taped pipes to get to the aspirator, I should use a short hose?

Thanks for any input.

pump.bmp - 243kB




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DJF90
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[*] posted on 2-7-2009 at 13:05


Your problem is that you are generating back pressure on the aspirator! your water outlet tube needs to be about 6 inches long and the end of it needs to be ABOVE the surface of the water, in order for it to work effectively. Or at least thats my opinion on the matter.
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entropy51
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[*] posted on 2-7-2009 at 14:40


Not all pumps work well for driving a particular aspirator. The pressure and flow delivered by the pump may need to be matched to the aspirator.

From your drawing, it appears that you may be drawing air bubbles into the pump, which is not good. DJF is right that the aspirator outlet should be above the water level.

There are several threads on this subject. Search using aspirator in the subject line and you will find them.
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Contrabasso
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[*] posted on 7-7-2009 at 11:47


What is the pump developing in terms of pressure and flow rate. You will probably need 1 - 2 bar and not a huge flow rate. You will also need to raise the aspirator so that the outlet has a tail pipe in the order of 6 - 12 inches and this is clear of the water reservoir.
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basstabone
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[*] posted on 9-7-2009 at 09:16


Another suggestion is to put a plate or a board between your pump and the aspirator which will hopefully increase it a bit. This will stop the air bubbles from coming in
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stateofhack
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[*] posted on 9-7-2009 at 15:43


Use a baffle! No air bubbles it should do the job!
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Vogelzang
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[*] posted on 9-7-2009 at 16:50


Use ice cold water.
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grndpndr
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[*] posted on 11-10-2009 at 10:43


What is the effect of 115degree F tap water on an aspirators vacuum?
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watson.fawkes
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[*] posted on 11-10-2009 at 12:34


Quote: Originally posted by grndpndr  
What is the effect of 115degree F tap water on an aspirators vacuum?
Higher ultimate pressure. More back-streaming of water vapor into the vacuum line, if that matters to your application.
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gsd
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[*] posted on 12-10-2009 at 04:19


Quote: Originally posted by grndpndr  
What is the effect of 115degree F tap water on an aspirators vacuum?


@grndpndr

You either do not read the replies to your questions or do not understand the answers or both.

Reply to this very question which you raised in the "Need help with vacuum distillation............" on 6 Oct. was posted on the same day in the same thread. Go read it and then come back if do not understand the technicalities.

gsd
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Klute
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[*] posted on 13-10-2009 at 19:36


I did the same mistake when I first built my aspirator, and used the same kind of pump. Thing is, these pump, 1° heat the water up significantly and quickly, 2°, and most importantly, are rather made to have a good flow than a good pressure (HMT= 10-15m). I had crappy vacuum with such pond pumps. I bought a cheap(er) external pump, made for watering your garden using water from a well, with a HMT of 35m.. But lower maximum flow (doesn't matter, high enough to suit the aspirator), and result: 20mmHg with cold water, and less rapid heating of the water.

Well, after a few hours use, the wtaer heats up to 35-40°C easily, but you just need to change it evry hour or so. Using ice is a waste as it melts very quickly and only gives you a couple torr less for a short period. Cold tap water much more practical, and gives 25-30mmHg.

There's a picture of my setup somewher eon this forum, if you want I can look up the technical data on my pump when I get the time to.




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