I was lucky enough to get a little 2" NRC diffusion pump at a hamfest last month, and I've thought about installing it on my demo fusor, at least until I start building a neutron model.
I may machine out an Aluminum disk and epoxy a hose barb into it, since the only way the diff pump can connect to my system would be through about 2 inches of 1" i.d. PVC hose.
Will using a plastic hose totally negate having the diff. pump in there at all?
Adam Parker
Diffusion Pump to baseplate
Re: Diffusion Pump to baseplate
I'd advise against the PVC hose... because of the high temps right at the High Vac inlet to your pump. Get some SS (preferably) or some metal line. The 1" diameter, wont help your throughput very much, but I am sure you will notice the difference in attained vacuum level.
Dave Cooper
Dave Cooper
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Richard Hull
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Re: Diffusion Pump to baseplate
The use of plastic hose on the true high vacuum side of a diff pump would be THE limiting factor of your system. The plumbing on the real low side (throat of the diff pump) should be ideally non-existant!! The throat should open right into your chamber.
We do not require the full 10e-7 torr vacuum that such a pump can ideally provide and a throttling back on the vacuum with plumbing and smaller valving of the throat is allowed.
Such plumbing should be glass or metal, however. I would not chokeoff a 2" throat below 1" with valves or plumbing. KF 25 stuff would be okay, but no hose of rubber or plastic should ever be used here.
Richard Hull
We do not require the full 10e-7 torr vacuum that such a pump can ideally provide and a throttling back on the vacuum with plumbing and smaller valving of the throat is allowed.
Such plumbing should be glass or metal, however. I would not chokeoff a 2" throat below 1" with valves or plumbing. KF 25 stuff would be okay, but no hose of rubber or plastic should ever be used here.
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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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quinnrisch
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Re: Diffusion Pump to baseplate
Interesting fact is that the best glass to use for very low gas permitivity is soda lime glass, that same stuff beer bottles are made out of.
Most polymers has notoriously bad for gas permitivity. They are used for medium vacuums, down to about 10-5 Torr, but they are generally not used at pressures below that.
Metal is usually the best because it can be welded and you can heat the metal to outgass all the crap off the inside of your chamber. NOTE: UV works pretty damn well too, but for UHV vacuums baked out is the quickest way, the UV won't get rid of as much stuff.
Also water is you biggest enemy in vacuum technology. It DESTROYS vacuums. At about 10-3 Torr almost all of the pressure in the chamber is water vapor, and VERY little is actually air. So never put wet stuff in your chamber and try to keep the system closed to atmosphere especially on humid days. I live in AZ and when it is humid I definitely see a marked difference in vacuum preformence.
As good tip always weld on the vacuum side of the chamber and or component.
Also try to prevent things from falling into your diff pump by either caution or working with gravity.
And in my experience pipe threading loaded up w/ teflon tape will be vacuum worthy to at least 10-5 Torr tighten well and installed correctly. I don't know if it is good below that range because I haven't gone below that vacuum.
Also AL is about the best He barrier there is, but Al is hard to weld. If you wanted to tighten your vacuum system you could do a thermal evaporation of Al on the inside of your chamber by using a peice of clean Al as a filiment.
Sorry there is so much in this post but I got carried away with my self
Most polymers has notoriously bad for gas permitivity. They are used for medium vacuums, down to about 10-5 Torr, but they are generally not used at pressures below that.
Metal is usually the best because it can be welded and you can heat the metal to outgass all the crap off the inside of your chamber. NOTE: UV works pretty damn well too, but for UHV vacuums baked out is the quickest way, the UV won't get rid of as much stuff.
Also water is you biggest enemy in vacuum technology. It DESTROYS vacuums. At about 10-3 Torr almost all of the pressure in the chamber is water vapor, and VERY little is actually air. So never put wet stuff in your chamber and try to keep the system closed to atmosphere especially on humid days. I live in AZ and when it is humid I definitely see a marked difference in vacuum preformence.
As good tip always weld on the vacuum side of the chamber and or component.
Also try to prevent things from falling into your diff pump by either caution or working with gravity.
And in my experience pipe threading loaded up w/ teflon tape will be vacuum worthy to at least 10-5 Torr tighten well and installed correctly. I don't know if it is good below that range because I haven't gone below that vacuum.
Also AL is about the best He barrier there is, but Al is hard to weld. If you wanted to tighten your vacuum system you could do a thermal evaporation of Al on the inside of your chamber by using a peice of clean Al as a filiment.
Sorry there is so much in this post but I got carried away with my self