Fusor Forums

It's been a while since I last posted. I have bought a 6 way 2.75" conflat cross to serve as a new main chamber. It will get here next week. Also, when I'm roughing the chamber out, the pressure drops to ~55 mtorr (still leaks) and then starts to slowly rise to 56 and then 57 as the pump starts to warm up. I disassembled and cleaned the pump, including one of the rotary vane stages, and got the chamber down to 55 mtorr, a 20mtorr improvement from before the cleaning. The rise in pressure still happens. Any idea what could be causing this?

What can the pump do at the head? Put a gauge directly at the pump inlet.

Richard Hull

At the moment, I am unable to deadhead the gauge. I got my new chamber in the mail today- it's a 6 way 2.75" conflat cross. Here is it assembled with used copper gaskets just for reference.




On a separate note, my school is building a 1MeV cyclotron starting next year. The project will be guided by Tim Koeth from UMD, and I had the pleasure of talking to him briefly after the school interest meeting for the cyclotron was over. Hopefully I will be fully involved in the project over the next few years- I am probably one of the more vacuum and high voltage knowledgeable students at my school currently (though I'm mostly still a newb), and I am sure that my "experience" building a fusor will help earn me a spot on the team.
-Liam

Just a quick note: I see that you're using some type of NPT threaded elbow adapter to connect the VCR flange on the 275 Mini, you did use a metal gasket seal between the VCR flange and the VCR->NPT coupling? These connections require silver plated SS crush discs which must be seated (and ideally centered) between the Male/Female VCR connections. I had a minor leak on my gas line which was affecting my ultimate pressure with the turbo on and the fix was as simple as utilizing vice grips and a wrench to tighten each VCR connection. Try placing ~90% isopropyl alcohol (denatured) or acetone on the flange seams and if you see the pressure climb even further than you've found your leak.

Just some food for thought.

Yeah, it's not the right fitting. I used it earlier by brazing a washer to the end to act as a rudimentary seal surface along with a cast solder gasket. It undoubtedly leaked and I'm replacing it with a VCR to KF adapter soon. It's just in the picture for "show". Do I need silver plated SS gaskets or can I use copper?

It think the gaskets are typically AG plated copper. The VCR fitting is a close relative of the old, much larger, Curvovac fittings that tried to work around the old conflat patents. I have some old 2.75 curvovac stuff hanging around the lab. In many ways, to my mind, it seemed like it would be better than conflats, but is just not seen now.

Richard Hull

Hmm. I guess LDS vacuum sells only plain VCR copper gaskets, which I assume will work fine.

Sure, they will do just fine. Just make sure to really tighten the fitting down good and firm. They make centering rings for those gaskets.

Richard Hull

It's been a while since I last shared my progress. I finally found a turbo pump! It's a Pfeiffer TPU 040 pump with TCP 040 controller, which was described as not working. Opening it up revealed a loose relay, and a quick atmosphere test confirmed that it was the problem. I now have a fully functional turbo system, and it only cost $150. All things considered, I made out like a bandit. Once a KF-40 to KF-16 adapter gets here, I'll test the pump on the chamber.
I'll post progress on my HV transformer soon.

-Liam David

Anyone know if I can run the TPU-040 pump horizontally, or will it destroy the pump? I have been unsuccessful in finding a manual.

Hi David

Manufacturer claims it can be mounted in any position.
I will leave a manual at Files forum.
Good luck!

Thanks!

That's a nice looking setup Liam. As someone looking to move from a demo fusor into neutron production your fusor has just become my goal. It looks so clean/simple and well organised. Great work to date and I look forward to seeing your progress.

There are some less professional parts of the setup that I'm not too proud of and that you can't see in the pictures, but thanks for the compliments. Smaller 2.75 conflat fusors don't produce as many neutrons as a 6" sphere or other larger chambers, but I went with this chamber because of costs.
-Liam David

Cost is a big concern for me as well. I'd love to be able to nail a large fusor but something in the 3" sort of realm is far more walletable. I can do a lot of the work myself although finding materials here can be difficult. Namely high voltage gear. It's seemingly not very common in Australia. I will figure something out. As we always do in this field.

As a very wise man once said, Physics is like sex. Sure, it has some practical applications... But thats not why we do it.

When I ran the turbo pump again today, I noticed that it made a loud "gurgling" sound for about the first ten seconds of acceleration and last 30 seconds of deceleration- otherwise it runs fine. I looked into the outlet with the pump spinning slowly and noticed that the rotor was vibrating slightly. I took the oil cap and rotor nut off, but the rotor does not come out. Can I force the rotor out with something like a bearing puller, or will this damage the pump? When the base is unscrewed, it does not come off, but does cause the rotor to seize. Does anyone have any experience disassembling a Pfeiffer TPU-040?

Another problem. I discovered that the top magnet ring in the turbo pump is cracked in two places. Could this be the cause of the rotor vibration?

Unless you are experienced with working with very tight machining tolerances and rotation speeds up to 90,000 RPM, I would not try to disassemble the pump. As long as it is quiet when it is up to speed and it's pulling the vacuum you need, I'd leave it alone. If not, I'd bite the bullet and send it off to a reputable rebuilder.

It makes some sort of a "gurgling" noise as it spins up- no liquids- but vibration. The "gurgling" noise fades out as it accelerates. I can also wiggle the rotor side to side if I push gently on it.

I have contacted a repair company and they say that when the magnet rings are cracked, the pump is irreparable. Is this true? The pump rotor can be disassembled with a spanner wrench, and ultimately everything had to be assembled, including the magnet rings, so...?

Cost to repair is most likely what they are referring to. Is it cost effective.

No, they're willing to inspect it for free to see if it's repairable, but one of the (technicians?) emailed me and said it's not.

The new TCP-040 controller arrived today, and I bolted the chamber together to do a vacuum test. The roughing pump only reached about 350mtorr due to outgassing, but the turbo pump pulled the chamber to 1E-5 torr in just a few minutes. The turbo accelerated fine and has a high, almost piercing pitch as it does so. At one point during deceleration it did sound like rotating metal contacted something in the pump, but no other noises were made afterwards.
In the manual for the turbo pump, it says that if the pump is mounted off of the vertical axis, then the outlet port should not exceed 20 degrees side-to-side from pointing downwards. What is the reasoning behind this?

-Liam

Admin, please grant me edit privileges so I can restore photos for some of my old threads.