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Author: Subject: Suitable manometer
Sulaiman
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[*] posted on 5-2-2023 at 17:08


My comments above give the impression that I favour mercury u-tubes etc.
I definitely do not,
I use and recommend Bourdon gauges of the type shown in the first few posts.

There are so many options for pressure/vacuum gauges but the cheap type are my choice.




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Yttrium2
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[*] posted on 5-2-2023 at 17:56


Are vacuums (<10mmHg) expensive??
I need 28 Inches Hg or higher.


Here is my conceptualization of the vacuum distillation setup minus the gas trap (the one that doesn't implode right?)

Which leads me to my next question, what kind of a trap do I need between my vacuum and the vacuum takeoff adapter?





IMG_20230205_174855859.jpg - 2.6MB



[Edited on 2/6/2023 by Yttrium2]
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Sulaiman
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[*] posted on 5-2-2023 at 19:29


Your diagram indicates that you want to do fractional distillations at low pressures.
I had such dreams too.

If there is a specific reduced pressure distillation that is very important to you, then go for it,

but I recommend that you work at atmospheric pressure only until you have a lot more practical experience,
by that time you will have a much better appreciation of what is required for your circumstances.
Not a criticism, just advice.

I'm still learning the hard way (mostly by failures) but I'm not in a hurry.
...........................
PS vacuum pumps for less than 10mmHg need not be expensive,
A peristaltic pump can be used for medium vacuum, low pumping rate applications
( my YT video https://m.youtube.com/watch?v=gGtYlS1ihbE)
A generic rotary pump (HVAC, car air-con service type) for medium vacuum at higher pumping rates
(either can give a gauge reading of - 1 Atmosphere)
I've not yet measured the actual minimum pressure of my rotary :)
High vacuum is only for the few.

[Edited on 6-2-2023 by Sulaiman]




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Mateo_swe
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[*] posted on 6-2-2023 at 04:20


Be aware that the thermometer in your drawing, if not secured enough can shoot down the condenser and break when using vacuum so make sure it cant slip down.
Using an aspirator and a water pump can get medium vacuum and have many good properties.
There is no vacuumpump to damage with corrosive chemicals or solvents.
If using a waterpump to feed the aspirator you can just circulate the water so water consumption is none but any chemical coming over to the aspirator goes into the circulating water (better than damaging the vacuumpump).
If putting ice in the waterbucket the vacuum is incresed, flow doesnt affect vacuum much as long its enough.
Its a cheap and good way.

Using a rotary vane vacuumpump can get you strong vacuum but chemicals get into the oil in the pump and the oil needs to be changed often.
Strong vacuum is quite dangerous, flasks can implode if not designed for high vacuum or if they have a small crack.

Chemical diaphragm vacuum pumps are designed to withstand chemicals and solvents, and are the best to use for chemical stuff but they are quite expensive.
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Sulaiman
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[*] posted on 6-2-2023 at 05:53


So it circles back to the beginning,
the above description applies to the unit Yttrium2 first considered !




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Cathoderay
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[*] posted on 6-2-2023 at 12:11


This video gives more information.
https://www.youtube.com/watch?v=tYLlkTDstmo
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Yttrium2
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[*] posted on 7-2-2023 at 08:59


Quote: Originally posted by Sulaiman  
Your diagram indicates that you want to do fractional distillations at low pressures.
I had such dreams too.

If there is a specific reduced pressure distillation that is very important to you, then go for it,

but I recommend that you work at atmospheric pressure only until you have a lot more practical experience,
by that time you will have a much better appreciation of what is required for your circumstances.
Not a criticism, just advice.

I'm still learning the hard way (mostly by failures) but I'm not in a hurry.
...........................
PS vacuum pumps for less than 10mmHg need not be expensive,
A peristaltic pump can be used for medium vacuum, low pumping rate applications
( my YT video https://m.youtube.com/watch?v=gGtYlS1ihbE)
A generic rotary pump (HVAC, car air-con service type) for medium vacuum at higher pumping rates
(either can give a gauge reading of - 1 Atmosphere)
I've not yet measured the actual minimum pressure of my rotary :)
High vacuum is only for the few.

[Edited on 6-2-2023 by Sulaiman]


Thanks for this! I was interested in seeing the peristaltic pump, -- I'm surprised the rollers do not tear up the tubing, but I guess they have less friction than some other configuration.
I like your video!

You say high vacuum is only for the few, -- I'm still trying to understand why?

[Edited on 2/7/2023 by Yttrium2]
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[*] posted on 7-2-2023 at 09:02


Quote: Originally posted by Mateo_swe  
Be aware that the thermometer in your drawing, if not secured enough can shoot down the condenser and break when using vacuum so make sure it cant slip down.
Using an aspirator and a water pump can get medium vacuum and have many good properties.
There is no vacuumpump to damage with corrosive chemicals or solvents.
If using a waterpump to feed the aspirator you can just circulate the water so water consumption is none but any chemical coming over to the aspirator goes into the circulating water (better than damaging the vacuumpump).
If putting ice in the waterbucket the vacuum is incresed, flow doesnt affect vacuum much as long its enough.
Its a cheap and good way.

Using a rotary vane vacuumpump can get you strong vacuum but chemicals get into the oil in the pump and the oil needs to be changed often.
Strong vacuum is quite dangerous, flasks can implode if not designed for high vacuum or if they have a small crack.

Chemical diaphragm vacuum pumps are designed to withstand chemicals and solvents, and are the best to use for chemical stuff but they are quite expensive.


Good point about the thermometer, how should it be affixed in vacuum distillation, -- are those ground glass thermometer thingy's the only option here?

Do you have example of a flask not designed for high vacuum? (Aside from a star crack etc..)

Last point, -- You mentioned diaphragm vacuum pumps being expensive, in the video Cathoderay posted, it is stated that they're cheap? I'm sure there is a range in prices for the different pumps but some clarification here?


[Edited on 2/7/2023 by Yttrium2]
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[*] posted on 7-2-2023 at 09:10


Thank you everybody for chiming in :)


I still have no idea of the range -- or is it level, in mmHg -- of vacuuum that the different pumps can produce.

Additionally I don't think <10mmHg is equivalent to 28 Inches Hg or higher, there must be a missing decimal point or something.



:)

[Edited on 2/7/2023 by Yttrium2]

[Edited on 2/7/2023 by Yttrium2]
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Cathoderay
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[*] posted on 7-2-2023 at 13:05


I think there is some confusion about the way the amount of vacuum is stated.

There is absolute pressure that is measured from complete vacuum, so 10mmHg above absolute vacuum is a pretty strong vacuum.
760mmHg would be atmospheric pressure, no vacuum at all.
Another common way to express a vacuum, especially if it is a high vacuum is Torr which is pretty much the same as mmHg absolute. Very high vacuum is very close to zero so it might be (10 to the minus 3) Torr. It is more and more difficult to get near zero. Mechanical piston or vane pumps can go down to about 1mmHg. As shown in that video aspirator pumps cannot go down that low.

The other way to measure vacuum is gauge vacuum, it is measured from atmospheric pressure. Zero would be no vacuum. A complete vacuum would be -760mmHg or about -30 inches Hg. Commonly if it is understood that you are talking about vacuum the "-" isn't used.

The bottom line is that the an aspirator is fine for filtering and distillation unless you want to distill oils or the like.
You don't have to be worrying about High Vacuum and Ultrahigh Vacuum and all that technology, you are not going to be distilling aluminum.

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[*] posted on 7-2-2023 at 13:51


Quote: Originally posted by Cathoderay  
I think there is some confusion about the way the amount of vacuum is stated.

There is absolute pressure that is measured from complete vacuum, so 10mmHg above absolute vacuum is a pretty strong vacuum.
760mmHg would be atmospheric pressure, no vacuum at all.
Another common way to express a vacuum, especially if it is a high vacuum is Torr which is pretty much the same as mmHg absolute. Very high vacuum is very close to zero so it might be (10 to the minus 3) Torr. It is more and more difficult to get near zero. Mechanical piston or vane pumps can go down to about 1mmHg. As shown in that video aspirator pumps cannot go down that low.

The other way to measure vacuum is gauge vacuum, it is measured from atmospheric pressure. Zero would be no vacuum. A complete vacuum would be -760mmHg or about -30 inches Hg. Commonly if it is understood that you are talking about vacuum the "-" isn't used.

The bottom line is that the an aspirator is fine for filtering and distillation unless you want to distill oils or the like.
You don't have to be worrying about High Vacuum and Ultrahigh Vacuum and all that technology, you are not going to be distilling aluminum.




I'm really lost now. I am able to take from this that there are two ways to measure vacuum.

Explain more please

And I take that I need rotary vane for oils and the like..


This is what I have so far,

Are these the two types of ways of measuring vacuum you were talking about ?

Screenshot_20230207-134759-280.png - 157kB
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[*] posted on 8-2-2023 at 13:59


I heard this would be used for a vacuum fractional distillation as a coupling. I thought it had to be a ground glass thermometer w/th adapter

[Edited on 2/8/2023 by Yttrium2]

Screenshot_20230208-135715.png - 129kB
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[*] posted on 8-2-2023 at 18:32


There are many devices that can be used to measure a vacuum level.
I was talking about two basic ways of expressing the level.
There are many units to express the vacuum level.

This is a typical mechanical rotary vane vacuum pump.
https://www.harborfreight.com/25-cfm-vacuum-pump-61245.html?...

On the other hand this is a mechanical chemical resistant diaphragm vacuum pump.
https://www.southernlabware.com/oil-free-laboratory-chemical...
Do you notice a difference in price?
I don't know why you are asking so many questions about pumps.
Just use an aspirator!
Also there is not universal distillation set up, how it is built depends on what you want to do. How much vacuum level you would need depends on what you want to do.

Maybe this explanation will help.
https://fluidpowerjournal.com/vacuum-measurement-a-basic-gui...
If you do some searching online you will find more info.

I have few questions for you.
What country are you in?
What level of schooling have you had?
I really don't have the time to cover an entire physics course about vacuum systems for you.
This is probably my last post on this thread.
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