Pressure comparison

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.
Post Reply
apollo
Posts: 100
Joined: Wed Jan 28, 2004 1:59 pm
Real name:
Contact:

Pressure comparison

Post by apollo »

Hello everybody
Working on this fusor is taking up a tremendous amount of time. I hope I'm moving in the right direction. My question is: am I actually lowering the pressure? My vacuum gauge was supposedly lost in the mail and it will be a while until I can get a new one. Here we go:

First:
http://www.fusor.us/fusorpics/plasma_first.jpg

Second (after an application of a large amount of Teflon tape on the 1/2" NPT threads)
http://www.fusor.us/fusorpics/plasma_second.jpg

Without the Teflon tape, there is an audible leak.

Right now I'm using a microwave oven transformer and 1/2 wave rectifier, later on I'll switch that to a 30KV X-Ray transformer. Those pictures were both at about 35-50ish volts on my variac (no higher than 60) which would translate to 800-900 volts. The second picture really appears to be a "cloud" of plasma whereas the first picture is more of the grid itself glowing. There are also visible striations on the part that is closest to the shell. On both tries, when the voltage was at 1200V+, there were small flashes appearing all over the place. I have a movie file (.mov) that I can upload if you all don't know what I'm talking about.

The frustrating part is that I called Robinair and they don't have any idea what the threads on this pump are! I called before and they said 3/8" Flare, and that's way off. 1/2" NPT is almost exactly right, but not quite. The thread pitch seems to be the same but it's about 1/32" too small. It's extremely frustrating! About the Welch Duoseal pumps, are they usually in workable shape when bought straight from eBay? What kind of repairs need to be made and is there some kind of "rebuild kit" that one can purchase?
User avatar
Mike Veldman
Posts: 155
Joined: Mon Aug 13, 2001 4:38 pm
Real name: Mike Veldman
Location: Stillwater, Oklahoma

Re: Pressure comparison

Post by Mike Veldman »

You might consider just threading the fitting out of the pump and taking it to the hardware or plumbing supplier and finding a flare nut to fit. Or, simply buy a new fitting to thread into the pump which matches your tubing.

Most of the used pumps I've purchased at various auctions, although not via ebay have been servicable. Just need flushing in most cases.

mike
I tried to contain myself, but I escaped.
apollo
Posts: 100
Joined: Wed Jan 28, 2004 1:59 pm
Real name:
Contact:

Re: Pressure comparison

Post by apollo »

"You might consider just threading the fitting out of the pump and taking it to the hardware or plumbing supplier and finding a flare nut to fit. Or, simply buy a new fitting to thread into the pump which matches your tubing."

The threading isn't removable. I already removed the T-fitting that had the 1/2" Acme and 1/4" MFL fittings on it and this is what is directly on the pump. I cannot find anything that will fit this and the manufacturer doesn't even know what kind of fitting it is, which makes it impossible to find the correct thread!

Also, what does flushing entail?
Starfire
Posts: 1482
Joined: Wed Oct 24, 2001 2:14 pm
Real name:

Re: Pressure comparison

Post by Starfire »

You are getting there Laim - the thread may be metric pipe. On the voltage, better not to use simple half-wave rectification, but use (as in a microwave oven ) as a doublier with the cap transformer fed and diode to ground. This will give you 5000 volts 0.25 A, from the MOT { which is normally 2500 volt on the secondary } and if you use a second cap and diode as a second stage, it will bring you to 10000 volts at about 100ma. If you feel brave and with suitable precautions you can up it to 20k with another stage - still at about 50ma. You will have to think about current limiting at this voltage as you could be running about 2 Kw otherwise. Microwave oven caps @ 1mfd will easy provide this. A quick easy 20kv power supply from a couple of scrap ovens
apollo
Posts: 100
Joined: Wed Jan 28, 2004 1:59 pm
Real name:
Contact:

Re: Pressure comparison

Post by apollo »

Okay, I found that a 5/8" Flare connector actually fits very well. However, the pressure still isn't dropping enough! Would it be OK to use pipe thread sealant (Teflon-'enriched') or would that outgas too much? I think I'm very close!
User avatar
Richard Hull
Moderator
Posts: 14992
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: Pressure comparison

Post by Richard Hull »

I am stunned that the robinair exit fitting has no threads into the body of the pump!! I have never heard of this!!

I would take that worthless refrigeration fitting and throw it as far away as I could. I have several Ritchie 6 CFM "Yellow Jacket" pumps. They have a large threaded fitting into the body of the pump. I removed this entire fitting and a gapping 1" diameter threaded hole is seen which is a common large taper pipe thread. A trip to a plumbing supplier yielded the proper brass fitting with a large hose barb with a 1/2 hole. for 3/4" hose. You could then just hook the hose direct with a clamp.

You will always need a vacuum ready thread sealant that dries not hard, but rubbery. (special product). Teflon tape is a pure joke....never use it.

You are working in the world of vacuum and not refrigeration, nor plumbing! Every component must be vacuum rated or vacuum adaptable. Small hoses in long length with small conductances will provide you with near worthless results.

The ideal is a 6" long hose 1" in diameter. The object is to set the pump immediately under the vacuum chamber. Anything other than this and the pump is just not doing anything much for you.

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
Post Reply

Return to “Vacuum Technology (& FAQs)”