Sciencemadness Discussion Board

High Vacuum Systems

akmetal - 23-11-2023 at 01:24

Hello everyone,

I just want to say I am glad I found this forum. I have recently aquired a used but in great condtion Varian oil diffusion pump type 0183 with a 9" 8 bolt flange on the top. I had originally bought it for building an RF sputter machine (which means I would also have to build a 13.56 mHz power supply.

Anyway I may end up using this to build an electron gun for a wiggler (I know that's ambitious but I could really use a free electron fully tunable powerful laser so I can get frequencies in between crystal and gas excitation frequencies.

So I am going to have to custom design a lid for this thing and a way to seal in my electron gun or sputter machine so how much open space do you have to leave between the diffusion pump and the space your evacuating, could I get a bunch of 1/4" 1/4 turn ball valves from Swagelok and machine a flange plate with a bunch of threaded connections to the vacuum space (kind of like how they do for making vacuum tubes only with valves)? IF so how many is adequate.

My understanding of the theory of operation is that molecules wander into the oil and get absorbed so the flow paths cant be to small.

Rainwater - 23-11-2023 at 07:50

Quote: Originally posted by akmetal  
My understanding of the theory of
operation is that molecules wander into the oil and get absorbed so the flow paths
cant be to small.

This is correct. With high vacuum things move very differently
Molecular repulsion is not a dominant force at low pressures.
Small tubes are bad, bigger the better. Minimum bends are desirable as well.
As for spacing, enough to ensure oil from the diffusion pump does not make it to
the vacuum chamber.

Material outgassing will be another issue. One of the factory I work with uses an old
vacuum oven to de-rust tools and heat exchanger. A defusion pump can suck the
oxygen out of rusty steel. Point being, if you find your pressure not reaching the
desired low values, consider outgassing

yobbo II - 23-11-2023 at 17:39



See the belljar.net

https://www.belljar.net/

Yob

Twospoons - 23-11-2023 at 17:52

As I recall, its common to have a cooled baffle in between the diffusion pump and the vacuum chamber to help stop oil backstreaming into the chamber. It will reduce your pumping rate though.
I would love to get my hands on a decent diffusion pump - but I've only ever seen them listed on Ebay in the US, and the shipping costs would be insane.

yobbo II - 24-11-2023 at 04:48



If you keep looking cheap ones can appear.

There is one listed here:
The description states that he got 10 - 5 torr vacuum no problem. Is that a typo or what?


https://www.ebay.co.uk/itm/134819147035?hash=item1f63d8ed1b:...

I am currently making a diffusion pump out of SS. A piece of SS pipe with tea pot pieces for the internals. Have the baffle (between pump and chamber) already made from SS and Copper. The copper flaps are water cooled.
It has a diameter of about 4 inchs.
The pump has three stages. It is difficult to solder the outside cooling pipe (copper) to stainless steel. Will have to pre-tin the SS using 5% silver solder(soft solder).
Will post some pics.
This post has reminded me if it.

Diffusion pumps (I believe) are more accurately called condensation pumps. The few(er) air molecules get trapped by the oil vapour at the higher vacuum end and fall to the bottom of the pump where they are released in a greater concentration where they are sucked out by the roughing pump.
There is usually a baffle between the diffusion pump and roughing pump too.

A butterfly valve is very often used between chamber and pump.
https://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=p233...



Why do you need a 13.56 MHz power supply for a sputtering supply. I though it was just DC.

Yob

[Edited on 24-11-2023 by yobbo II]

Sulaiman - 24-11-2023 at 06:45

Quote: Originally posted by akmeta  
I would also have to build a 13.56 mHz power supply.
the frequency of 13.56 MHz is so that the rfi is in an ISM band, nothing special otherwise.
Ready made amateur radio HF amplifiers or modules or kits may suit you,
What power level are you considering?

akmetal - 24-11-2023 at 12:24

Quote: Originally posted by Sulaiman  
Quote: Originally posted by akmeta  
I would also have to build a 13.56 mHz power supply.
the frequency of 13.56 MHz is so that the rfi is in an ISM band, nothing special otherwise.
Ready made amateur radio HF amplifiers or modules or kits may suit you,
What power level are you considering?


I think I was looking at 1kw and those units were well over $1000 which is why I was looking to build one. I am also working on building my circuit design intuition at a detailed level.

I live in Alaska so I dont really care about the ISM band because theres few people to interfer with but its a good technical challenge to create such an obscure frequency.

The reason I was going with RF sputter is that its my understanding you can do thin film coatings of materials that are lower conductivity such as DLC grapite coatings etc. But if I end up making it into an electron gun I wont need that elaborate power supply, I might need an avalanche pulse generator though which is a curious device.

[Edited on 24-11-2023 by akmetal]

[Edited on 24-11-2023 by akmetal]

akmetal - 24-11-2023 at 13:59

Could something like this be remote mounted - https://www.foxvalve.com/mini-eductors/mini-eductor-dimensio...

Use a 24/40 to hose barb and a hose barb to threaded connection to the eductor and then use a large fish tank bubbler as motive gas to a barbed fitting and hose to the outside of the building?

Cathoderay - 24-11-2023 at 17:10

akmetal
Did you look at the datasheet for these things?
I don't think you have any idea of how difficult generating high vacuum without the proper methods is.
Look at this chart.
https://www.tedpella.com/company_html/vacuumcov.aspx
Another point of reference is that water boils at room temperature if the vacuum is stronger than 29" Hg.



[Edited on 11/25/2023 by Cathoderay]

akmetal - 24-11-2023 at 20:06

Quote: Originally posted by Cathoderay  
akmetal
Did you look at the datasheet for these things?
I don't think you have any idea of how difficult generating high vacuum without the proper methods is.
Look at this chart.
https://www.tedpella.com/company_html/vacuumcov.aspx
Another point of reference is that water boils at room temperature if the vacuum is stronger than 29" Hg.



[Edited on 11/25/2023 by Cathoderay]


Ops sorry 2 different applications, this is for just making sure I have enough vacuum to preferentially flow NO2 out of my reactor vessel to the outside rather than through the 24/40 joints.

For my real vacuum system I will be using a 500 micron roughing pump and the oil diffusion pump I recently aquired. i am still trying to think of how I can connect up the apparatus I want high vacuum on to the oil diffusion pump and be able to disconnect them without lossing the vacuum.

BromicAcid - 25-11-2023 at 06:12

Quote: Originally posted by yobbo II  

The description states that he got 10 - 5 torr vacuum no problem. Is that a typo or what?


Should be 10-5torr

yobbo II - 25-11-2023 at 07:04


Thanks Bromic!!

akmetal - 3-12-2023 at 01:39

What do you guys use for cleaning scale out of cooling lines. Starting to clean up that Variac oil diffusion pump I aquired. Took the fittings off the cooling lines and it needs some descaling/flush.

I was reading that citric acid would do the trick but also read that muric acid is used. Citric would be nice to avoid having to deal with one more nasty chemical/acid .... but it also needs to work.

Rainwater - 3-12-2023 at 02:14

Depends on the coil material.
Steel - 0.5% solution of sulfamic acid
Copper - 0.5% hcl solution
Aluminum - 0.5% nitric acid

Setup a pumping system and flow the cleaning fluid for at least 24 hours.
Use of a more consentrated solution can result in pitting but works faster.

If time is not a factor, using cold saturated sodium chloride solution is safe for all materials.

akmetal - 9-12-2023 at 12:23

Awesome thank you :)
Quote: Originally posted by Rainwater  
Depends on the coil material.
Steel - 0.5% solution of sulfamic acid
Copper - 0.5% hcl solution
Aluminum - 0.5% nitric acid

Setup a pumping system and flow the cleaning fluid for at least 24 hours.
Use of a more consentrated solution can result in pitting but works faster.

If time is not a factor, using cold saturated sodium chloride solution is safe for all materials.