Sciencemadness Discussion Board

Suitable manometer

Yttrium2 - 12-1-2023 at 11:06

What's the best and or simplest way to measure the vacuum level?

Some pumps have vacuum gauges on them, are these suitable?

Trying to conceptualize how a vacuum distillation is pieced together, and right now I'm perplexed by the vacuum

[Edited on 1/12/2023 by Yttrium2]

[Edited on 1/12/2023 by Yttrium2]

Yttrium2 - 12-1-2023 at 11:08



41g5t2SwmML._AC_SY1000_DpWeblab_.jpg - 23kB

yobbo II - 13-1-2023 at 16:58



A gauge that reads from zero to about 30 Torr would be fine AFAIK.
Some vacuum distilations are done at very low pressure if the substance is very temperature sensitive.

There is a simple vacuum controller attached which may be very useful.


Yob

Attachment: 10.1063_1.1137334.pdf (387kB)
This file has been downloaded 133 times


Mateo_swe - 23-1-2023 at 05:34

A common vacuum gauge.
One of these


I guess you could bend a glass tube to a U-shape using a torch and fill it with liquid mercury.
But you would not know how much vacuum each level represents without calibrating it with another vacuum gauge.

[Edited on 2023-1-23 by Mateo_swe]

Rainwater - 23-1-2023 at 16:30

Quote: Originally posted by Mateo_swe  
A common vacuum gauge.
I guess you could bend a glass tube to a U-shape using a torch and fill it with liquid mercury.
But you would not know how much vacuum each level represents without calibrating it with another vacuum gauge.

[Edited on 2023-1-23 by Mateo_swe]

You just need an accurate way to measure length.
10 inHg = 10 inches of mercury.
Diameter of the tube is irrelevant.

Yttrium2 - 23-1-2023 at 17:04

I guess what I was meaning to ask in my initial thread to be specific is this:


Is this how a vacuum distillation is done?

Adjust vacuum to level or more than compound of interest...

Does vacuum reach a certain vacuum level and stop pumping or is it continuously pumping to keep air evacuated and the vacuum level maintained?

Sorry, I was very vague here

Rainwater - 23-1-2023 at 17:20

The type of vacuum in the picture is a water aspirator-based device.
You add water and ice to the container, and it starts pumping.
With room-temperature water you will get about 15inHg of vacuum
It runs continuously.
From what I have read, most people continuously run their vacuum when doing distillation with a soft vacuum.

yobbo II - 26-1-2023 at 11:12

"I guess you could bend a glass tube to a U-shape using a torch and fill it with liquid mercury.
But you would not know how much vacuum each level represents without calibrating it with another vacuum gauge."

You would measure the difference in height of the two Hg coloumbs (or am I missing something).

You could use vacuum oil instead of Hg. Not toxic, cheaper, less dense and therefor would give more resolution.

See the belljar.net look in publications, the first five years for an oil manometer.

NOTE: I don't have any shares in the Bell Jar. :D

Yob

CharlieA - 26-1-2023 at 14:04

@yobbo II
You are correct; the difference in height of the two columns is the pressure in the system; one arm of the U-tube is open to the atmosphere, and the other is connected to the system. Of
course the height of the U-tube should be somewhat more than 760 mm to allow for an ambient atmospheric pressure greater than 1 atmosphere.

A quick search yielded this company that has many different manometers:
https://www.globaltestsupply.com/product/dwyer-1221-8-w-m-ma...

arkoma - 26-1-2023 at 18:31

i use a gauge off of an old refrigeration charging rig which i got a pawn shop for next to nothing, reads down to 30 inches and is fairly accurate. be VERY careful if you start pulling vacuum on things--warm liquids can suddenly flash boil, and NEVER NEVER pull vacuum on a standard erlenmyer flask. i KNOW better and yet thought that i could quickly do a vacuum filtration. imploded a 2 liter flask with hot aqua regia in it.

don't be me!

Yttrium2 - 30-1-2023 at 22:37

Would this be useful in the conceptualization of the u tube?

https://phet.colorado.edu/sims/html/under-pressure/latest/un...


It is interesting, coming from the world of a scuba diver learning how much an atmosphere was and how much pressure there was with how much depth, and then thinking about how that all goes out the window if we are dealing with gasoline on Jupiter.



Yttrium2 - 30-1-2023 at 22:59

What impact does gravity have on the depth pressure relationship?

Mateo_swe - 3-2-2023 at 03:10

So if a DIY U-shaped glass manometer filled with merqury is made to be used as a vacuum gauge it must be at least 30 inches tall (about 760mm).
Doesn it matter how much mercury is put inside?

Sulaiman - 3-2-2023 at 07:43

If the sealed end of a u-tube is full of mercury,
ie no air = no air pressure = vacuum

If you only want to measure low pressure
eg below 20mmHg then you only require a short u-tube.

At the open end of the u-tube, if the pressure (of whatever is attached) is zero,
mercury will be at the same height in both sides of the u-tube = half way up the ruler = 0 mmHg,

With a pressure of 20 mmHg the mercury will rise 10 mm in the sealed side,
and fall 10 mm in the other (open) side
etc.

So you'd only need a common 12 inch glass tube for 0 to 100 mmHg.
Plus the mercury.

I guess vacuum oil might work for (10x) lower pressures

Rainwater - 3-2-2023 at 08:18

Any liquid will work as long as you correct the scale
And stay above the vapor pressure
Water is well studied and cheap.
Glycol is used in the gauge showen above

unionised - 3-2-2023 at 10:20

Quote: Originally posted by Sulaiman  
If the sealed end of a u-tube is full of mercury,
ie no air = no air pressure = vacuum

If you only want to measure low pressure
eg below 20mmHg then you only require a short u-tube.

At the open end of the u-tube, if the pressure (of whatever is attached) is zero,
mercury will be at the same height in both sides of the u-tube = half way up the ruler = 0 mmHg,

With a pressure of 20 mmHg the mercury will rise 10 mm in the sealed side,
and fall 10 mm in the other (open) side
etc.

So you'd only need a common 12 inch glass tube for 0 to 100 mmHg.
Plus the mercury.

I guess vacuum oil might work for (10x) lower pressures

These sorts of (mercury) manometers are great, but you need to be careful with them.
A sudden change in pressure will slam the mercury into the end of the tube and that can break the glass.
Having a restriction in the middle of the "U" will help.

Yttrium2 - 4-2-2023 at 20:31

What is the appropriate manometer I can fill with water that would also work with Hg? -- That I can take measurements on -- to better understand the relationships between variables, and the usage of tools to make those measurements?



Screenshot (11).png - 508kB

Yttrium2 - 4-2-2023 at 20:33

(I guess I have to know at what vacuum level or whatever my stuff comes off at, get the right gauged, or column reading level in -- what is the frequently referred to term? inches of mercury, or was it mm??? Why does the above poster say that the mercury manometer is great? I was previously thinking that they were necessary, for some reason, I forget what that reason was.

Mateo_swe - 5-2-2023 at 08:32

The round common vacuum gauges (the pic i posted in my post erlier in this thread) is the easiest to use and are cheap.
I dont think they are super exact but they dont have the risk of mercury spill that a U-shaped glass gauge has if a sudden fast pressure change is happening like a hose disconnecting.
I dont know how good the are at handling chemicals, the U-shaped mercury tube is probably much better in that regard.
The U-shaped type can also be filled with other liquids but they must be made longer i think and preferably calibrated with another vacuum gauge.
There are also the digital vacuum gauges, these are very good but cost a bit of money especially a good brand one.
These are also sensitive for corrosive chemicals but is very handy to use to calibrate/check any other vacuum gauges you have.

Yttrium2 - 5-2-2023 at 10:07

Quote: Originally posted by Mateo_swe  

There are also the digital vacuum gauges, these are very good but cost a bit of money especially a good brand one.
These are also sensitive for corrosive chemicals but is very handy to use to calibrate/check any other vacuum gauges you have.


point noted

Yttrium2 - 5-2-2023 at 10:12

What are these for?

Do they have any clever repurposed applications?

[Edited on 2/5/2023 by Yttrium2]

Screenshot (12).png - 349kB

[Edited on 2/5/2023 by Yttrium2]

Mateo_swe - 5-2-2023 at 10:43

Those sets with vacuum pump and a vacuum vessel is for degassing epoxy and polyurethane glues so there is no bubbles in it when it hardens.

Yttrium2 - 5-2-2023 at 13:08

so for a vacuum distillation setup I need:

Pump, gauge, vacuum trap flask, tubing, hosing clamps?

-- What are some cool physics experiments I could do with the above listed!?

Cathoderay - 5-2-2023 at 13:11

Some general points.
Vacuum and pressure are measured in several different units.
The difference between atmospheric pressure and a vacuum can be in mm of mercury (mmHg), inches of mercury ("Hg) or inches of water, and that is just in the US. 25.4 mmHg equals 1"Hg equals 13.5"water. The difference between the mercury and the water measurement is due to mercury being 13.5 times denser.

A pressure difference of one atmosphere is 760mmHg, or 30"Hg, or about 32 feet of water, so if you wanted to measure a total vacuum and use water in your manometer it would have to be more than 32 ft tall. On top of that is the vapor pressure of water, it would start to boil at room temperature at about 29mmHg.

An aspirator can generate about 26-27 "Hg of vacuum. Mechanical pumps can get lower. Some types of mechanical vacuum pumps should not be used if the vapor is corrosive or otherwise damaging to the pump.




Yttrium2 - 5-2-2023 at 16:01

Thanks for clarification everybody, I've got enough here to digest now for a while.

Sulaiman - 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.

Yttrium2 - 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]

Sulaiman - 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]

Mateo_swe - 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.

Sulaiman - 6-2-2023 at 05:53

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

Cathoderay - 6-2-2023 at 12:11

This video gives more information.
https://www.youtube.com/watch?v=tYLlkTDstmo

Yttrium2 - 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]

Yttrium2 - 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]

Yttrium2 - 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]

Cathoderay - 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.


Yttrium2 - 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

Yttrium2 - 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

Cathoderay - 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.

Yttrium2 - 9-2-2023 at 09:16

Quote: Originally posted by Cathoderay  
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.


More than happy to answer, I live in California. level of schooling, -- some community college with H.S. diploma... Got to general Chem 1, passed it. A strong prealgebra background. (I hope) -- and some basic algebra skills. Its been years since my English writing classes, so I might be a little off when it comes to the way things are worded, hopefully they are making sense.

I actually have almost everything complete at community college accept the chemistry, physics, math and foreign language. got a D in art, not sure if that will transfer over ok, I can no longer audit it at one of my JC's...

And I've lurked and been here and around at other forums and such for the last however long since around 2005'

shroomery, wd, various automotive forums sciencemadness... --
Dad taught me a few things growing up'
Mainly, I probably wouldn't be into Chemistry if it wasn't for him.

Perhaps life has dealt me a different hand, perhaps I'm too lazy to learn -- Is that latter a logical proposition? One thing is for sure, I'm still committed to learning chemistry and getting a degree. I spent the last 3 years on probation, moving from house to house, jail to jail, program to program, out of my locale. It has been difficult having momentum during this times but I have managed to study, some, -- surely, not to the level that I would have liked too.

Currently, I'd say I'm in Algebra1, General Chem1-- Although, I'll probably want to go back or something here, too.

I have about 3 straight years of math required for my degree, and foreign language. I'm bad at stacking classes with math. -- I will probably take 1 math class at a time and then physics / chemistry. -- Not sure when I'll study foreign language, it seems like it will really detract from learning math chemistry and physics. If I take 1 course at a time, things might get stretched out too far and I might start forgetting by the time I'm done with the foreign language, I might have forgotten some of the math? -- Or something? -- It has been this way with English, and perhaps a few other subjects.
Anyways, that's a bit of my story and plan, to focus on solely math for as long as it takes. -- Even still, patience seems to be key for me...




Cathoderay - 9-2-2023 at 18:16

I wasn't after so much detail about your background.
If English wasn't your first language that might explain some difficulty following what I was saying.
The bit about probation and jail came as a surprise.
I have heard reports that the U.S. high school classes are poor in the sciences these days. That's sad because high school science should be the foundation of further science education.
Perhaps you have been too focused on chemistry and missed some physics and other sciences. Of course mathematics is needed in any science pursuit.
You should try learning more on the internet on many sites and even books at the library. This forum cannot fill all your needs. I certainly don't have time to answer all you questions, few people would.
I remember learning how barometers were made and worked when I was in high school. Maybe you weren't paying attention.
This site is good for some physics, interesting stories.
https://www.youtube.com/watch?v=oooS4Odq3PY

Yttrium2 - 20-2-2023 at 15:38

How many mmHg can this pull? It says .098Mpa


Or at what temperature can I boil water under full vacuum with this device?

41g5t2SwmML._AC_SY1000_DpWeblab_.jpg - 23kB

Is this accurate?

How many mmHg does it pull!??? -- So at what temperature does water come over at this vacuum? -- I'm a little confused here, please elaborate, thank you!!!!

[Edited on 2/21/2023 by Yttrium2]

[Edited on 2/21/2023 by Yttrium2]

Screenshot (42).png - 142kB

Yttrium2 - 20-2-2023 at 17:21

WE ARE AT 1 ATMOSPHERE HERE AT SEA LEVEL

1 ATM = 101325 PASCALS


101325 PASCALS
-98000 PASCALS (VACUUM LEVEL OF APPARATUS)

=
3325 PASCALS

= 24.93955 MILLIMETERS OF MERCURY.


= .98 inches of Hg


-Coincidence the vacuum level of the aspirator was .098 mpa?


Help I'm lost. EEEk!!!!


[Edited on 2/21/2023 by Yttrium2]

[Edited on 2/21/2023 by Yttrium2]

Yttrium2 - 20-2-2023 at 17:54

(rereading everything - one sec)

[Edited on 2/21/2023 by Yttrium2]


Ok so it still befuddles me how they figured out how much vacuum the vevor aspirator can pull?

[Edited on 2/21/2023 by Yttrium2]