Pumping Setup - A Few Questions

Every fusor and fusion system seems to need a vacuum. This area is for detailed discussion of vacuum systems, materials, gauging, etc. related to fusor or fusion research.
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Nicolas Krause
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Pumping Setup - A Few Questions

Post by Nicolas Krause » Sun May 24, 2020 12:00 am

Hello,

I figured I'd ask these questions in this forum rather than in the mega thread I've been working on. I believe I've got all the bits together to properly seal up the chamber and pump it down. I recall reading somewhere on this forum that someone was of the opinion that the turbo pump should not be in a direct line with the vacuum chamber due to the possibility of something falling into the chamber and destroying the turbo. However the manual for my turbopump shows diagrams with a short straight connection to the chamber, so I'm not too sure which is ok or if it matters at all. I have a 90 degree conflat connector that I could use to move the turbopump to a different angle, but would that reduce my pumping efficiency? Secondly the butterfly valve I've purchased has a seemingly different type of sealing edge than the knife edge used with the copper conflats. Can I use a copper conflat with it or do I have to switch to an o-ring of some type? If I have to switch to the O-ring will with work to connect to the knife edge conflats I have on all my other connectors?

ChristofferBraestrup
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Re: Pumping Setup - A Few Questions

Post by ChristofferBraestrup » Sun May 24, 2020 12:09 am

There is nothing 'wrong' having the turbo directly in-line with your vacuum chamber per se. Many a commercial turbo system is built this way. HOWEVER:

if debris falls into the pump, it will tear itself apart very fast and very energetically.

Turbo pumps works by diffusion, there is no flow of gas into the pump. This means everything making the diffusion path longer, or making the path narrower will affect pumping speed. Some turbos has a grating above them to catch debris, which is a good security measure, with the cost of increased pump-down time.

For a small-ish system I would worry more about debris than pumping efficiency. If you can mount your turbo horizontally or opside down that helps a lot too, but not all pumps has bearings fit for this.

A picture of the valve flange in question would be helpful.

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Nicolas Krause
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Re: Pumping Setup - A Few Questions

Post by Nicolas Krause » Sun May 24, 2020 12:30 am

Thank you for the clarifications Christoffer. A picture of the butterfly valve is below.
IMG_1063[1].JPG

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Re: Pumping Setup - A Few Questions

Post by John Futter » Sun May 24, 2020 6:58 pm

Nicholas
that will need an o-ring

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Re: Pumping Setup - A Few Questions

Post by Ameen Aydan » Thu May 28, 2020 10:51 pm

Hello,

I believe that most turbo pumps can operate sideways or upside down. The design of your chamber may make that a little harder to pull off but it shouldn't be too bad. Do you mind showing us the pump you are using? If you can find the manual it should mention what direction the pump can be mounted.

I'm stuck with a 90 degree 2.75" bellow valve but I have a small chamber (4.5" cross) so I don't imagine the pump down speed will be affected too much. I've seen much less efficient designs work just fine for smaller vacuum chambers.

Regards,
AA

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Richard Hull
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Re: Pumping Setup - A Few Questions

Post by Richard Hull » Fri May 29, 2020 6:36 am

As you can see in my long post on fusor V, I have two right angles in my long turbo to chamber plumbing. The volume of the cross is so tiny it pumped down nearly instantly to 10e-5 torr and still lower once the pump got up to speed.

My turbo has the official Pfeiffer protective screen mounted in the throat but it is rather worthless due to the two 90 degree turns in the high vacuum line to the chamber.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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