Vacuum Chamber Purchase/Size

For posts specifically relating to fusor design, construction, and operation.
Tyler Christensen
Site Admin
Posts: 551
Joined: Tue Feb 24, 2009 2:08 am
Real name:

Vacuum Chamber Purchase/Size

Post by Tyler Christensen » Tue Feb 24, 2009 2:11 am

I'm looking at vacuum chambers since this seems to be the hardest part to acquire, and I'm wondering where to get one. I've been looking at vacuum stores online but it seems like spherical steel chambers are upwards of $7000.

Where can I get one on a budget? Do I have to make one? I don't have any welding experience.

Also how large does it have to be for fusion?

MarkS
Posts: 250
Joined: Sat Jun 30, 2007 8:07 am
Real name:

Re: Vacuum Chamber Purchase/Size

Post by MarkS » Tue Feb 24, 2009 2:56 am

Contact Sharon Vacuum in MA.

Tyler Christensen
Site Admin
Posts: 551
Joined: Tue Feb 24, 2009 2:08 am
Real name:

Re: Vacuum Chamber Purchase/Size

Post by Tyler Christensen » Wed Feb 25, 2009 12:04 am

They said it would still be $1100 for a 6"... I was hoping to keep it to around $300 max, is this not realistically possible?

Also 6" inner diameter is enough right?

jlangridge
Posts: 34
Joined: Mon Aug 27, 2007 1:01 pm
Real name:

Re: Vacuum Chamber Purchase/Size

Post by jlangridge » Wed Feb 25, 2009 2:36 am

Why not do what Dan DT did and use a pressure cooker? You can generally find them for cheap on ebay or your local goodwill.

For details on his chamber try viewtopic.php?f=18&t=7805&hilit=pressure+cooker#p55764

good luck,

John Langridge

Tyler Christensen
Site Admin
Posts: 551
Joined: Tue Feb 24, 2009 2:08 am
Real name:

Re: Vacuum Chamber Purchase/Size

Post by Tyler Christensen » Wed Feb 25, 2009 4:07 am

That is an excellent idea. I see he only got it to 100-200 microns, but doesn't fusion require 10-20 microns? That could just be his setup though, or would it risk implosion any lower?

jlangridge
Posts: 34
Joined: Mon Aug 27, 2007 1:01 pm
Real name:

Re: Vacuum Chamber Purchase/Size

Post by jlangridge » Wed Feb 25, 2009 4:14 am

Whether a pressure cooker would implode would be dependent on the design and any flaws (especially with a used model). Most that I have seen are very sturdy even after large amounts of use. Keep in mind that pressure cookers are not designed for vacuum and there are going to be limitations. There was quite a bit of discussion about this as I recall. You might use the search feature and see what you can find...

It might be best to prototype with the pressure cooker and work out the bugs (Vacuum , electrical, gas flow, etc) with a demo fusor and then graduate up to a more expensive chamber later, when one comes available (they do from time to time show up on ebay)...It certainly is a cheaper solution if you are just getting your feet wet.

John Langridge

Tyler Christensen
Site Admin
Posts: 551
Joined: Tue Feb 24, 2009 2:08 am
Real name:

Re: Vacuum Chamber Purchase/Size

Post by Tyler Christensen » Wed Feb 25, 2009 5:26 am

OK, I'll look into getting one for my first build. If it takes the vacuum low enough, it is possible to fuse in it right? It doesn't have to be a sphere or anything by my understanding.

Also as a different question, are there any guides for making grids and exactly what shape they need to be etc? I haven't seen much discussion or pictures of the actual grid construction, just vacuum and voltage stuff

jlangridge
Posts: 34
Joined: Mon Aug 27, 2007 1:01 pm
Real name:

Re: Vacuum Chamber Purchase/Size

Post by jlangridge » Wed Feb 25, 2009 5:37 am

As I recall from the various discussions, the weak area of the pressure cooker is the gasket, since the cooker isn't designed for vacuum. I don't believe shape is an issue as guys are using cylinders and crosses for vacuum chambers and they are not necessarily symmetrical. Would be something good to search. I think if you can hit the proper pressure and have the energy in your PS to achieve fusion, it should work like a spherical chamber.

have a look around the various forums - there are a number of different grid designs that are detailed.. you can see many of the designs in the images section. I think the big prerequisite is survivability in the hostile plasma environment. There is quite a bit of discussion about this. Don't be afraid to experiment with various materials.

John Langridge

Dan Tibbets
Posts: 578
Joined: Thu Apr 17, 2008 5:29 am
Real name:

Re: Vacuum Chamber Purchase/Size

Post by Dan Tibbets » Wed Feb 25, 2009 10:45 am

Concerning my Pressure Cooker Demo Fusor-
The gasket in this example is flat with a groove on the inside surface. The lid sets on the gasket directly, and is locked by turning. There is some play and I occasionally have to push the body of the pressure cooker against the lid ( pinch with finger and thumb) untill a tiny vacuum is obtained. Once a strong vacuum is obtained there is probably ~750 lbs pushing down on the lid to maintain a seal (no clamps needed). This gasket design seems to be a common approach, but other brands may not work. Both the lid and body are grounded. The lid is curved, so when I cut a hole for the portview port the O ring would not seal with just vacuum pressure to hold it, so I had to epoxy a flat flange that was polished smooth (no scratches). The glass is held in place by the vacuum. A 7/8 inch gasked was to small- not enough pressure to compress the gasket and form a good seal. The only drawback is that when the vacuum is released, the glass can (and has) fallen on the floor. A retaining system would help, but that is for another day. I figure the vacuum is compressing the 1.5 inch gasket of the view window with ~ 23 lbs of force. How much pressure is typically applied with a bolt down retainer?
I had leaks in my plumbing. As mentioned in other threads, teflon tape seemed to leak. Silicone gasket material seem to work well as a thread sealer (and is cheaper than Locktight).
Despite the small bore of my tubing and needle valves, I was occasionally able to get down to ~35-60 microns. With the thermocouple gauge isolated at the used rotery pump head I could get down to ~ 22 microns.

The feedthrough has been my biggest problem. Using 1 inch threaded copper or PVC hardware with an o-ring and a nut to hold and seal it in place and filled with epoxy seems to work well, except even with a glass or ceramic tip the epoxy doesn't like the heat, If it gets hot enough it carbonizes (?) and/ or vaporizes. I need to figure out some way to conduct the heat to the shell faster, use different materials, or perhaps return to a spark plug with adaptations that have been recomended by several members of the forum.

The biggest advantages of the pressure cooker, at least for a demo fusor, is that it was cheap ($5 used). I've spent much more for the various hardware store brass valves, nipples, glues, etc. The other advantage is that it only takes ~5 seconds to open the system to access the grid, play with magnets, etc. Also, it is big enough to mount a mirror inside for a lateral view to go along with the top down view- Two for One bargain. The only essential tool was a drill (plus pliers, skinned knuckles, various choice words, etc).


Dan Tibbets

User avatar
Chris Bradley
Posts: 2930
Joined: Fri May 02, 2008 11:05 am
Real name:

Re: Vacuum Chamber Purchase/Size

Post by Chris Bradley » Wed Feb 25, 2009 12:29 pm

TylerChristensen wrote:
> That is an excellent idea. I see he only got it to 100-200 microns, but doesn't fusion require 10-20 microns? That could just be his setup though, or would it risk implosion any lower?


I hear this often, and presume it is just an 'old-chestnut'. At 100 microns, the external pressure on a vacuum chamber is about 14.5psi. At a billionth of a micron it is about 14.5psi. *Increase* of implosion probability at vacuums lower than 100 microns = approx zero. Is this not so? I've never really considered it otherwise.

The issue for lower than 100 microns is that you'll draw off outgassing contaminants from the seals, out of the metal, &c.. which will effectively stop you getting lower vacuums.

Post Reply