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Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
GrantX wrote ...
Ash, those are some serious industrial components, that gate valve is enormous! Is the single stage jigtool pump and the small speedivac pump far superior to my 2-stage Chinese pump? The speedivac isn't too expensive if I absolutely require an upgrade from the Chinese pump.
I think the Jigtools pump is an Edwards copy, or something. (that's what it looks like to me)
I prefer the old belt drive pumps because they are usually cheap, you can still get service kits for all the old Edwards units, and they are easy to re-build. I assume both will be better than your chinese unit, (assuming they are in reasonable condition) because they are designed as roughing pumps, so should achieve the figures quoted by JohnF earlier in this thread (or was it the other thread?).
Obviously, buying an old unit involves some risk as far as condition goes, but the old Edwards and Welch units are pretty good.
On the subject of bell jars, bell jars need a special 'L' shaped seal, made of rubber, which will outgas at low pressures. They can also break, but in my experience do not generally implode, it starts with a crack, and gets worse, just leaks. I once designed a replacement steel bell jar with a plastic window for a place I once worked as the technicians kept cracking the glass ones. The steel one used the seal from the bell jar.
I would consider other alternatives for a chamber, before buying a bell jar, depending on what you plan to use the system for in the future.
It took me a while but eventually I managed to find a nice flange on ebay, quite convenient, the bottom is a standard iso250...so I can use a iso250 blank off plate the top has a o-ring roove so its perfect for a glass plate and the lateral is iso63 so also quite standard and easly adapted to a connection to the pump.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
There are many interesting and exciting experiments you can do with the medium vacuum you can achieve with a good air conditioning pump.
You can make glow discharge devices, make more reliable N2 lasers, sputter metallic coatings, and you can even make your own Geiger–Müller tubes and gas switches. .
Partial pressure experiments: If you backfill your chamber with helium balloon gas, and pump it down again, the mean free path of electrons will be increased, with all sorts of exciting possibilities.
Registered Member #4074
Joined: Mon Aug 29 2011, 06:58AM
Location: Australia
Posts: 335
I've bought some ball valves and all the required brass fittings to connect everything together. Now, I will just need appropriate adapters for the vacuum gauge and chamber connections (I've got brass plugs so I can do tests without a gauge). I haven't found a decent chamber yet, but in the mean time I think I will build a mini-chamber out of a small jam jar, with a gasket and lexan plate as a base. I have some resistorless spark plugs that I could modify and epoxy in place as HV feedthroughs. The jam jar is only 250mL or so, and very heavy duty so I don't think it will crack.
I will make sure to post pictures as things progress - now I just need to wait for the rain to stop.
@ kludgesmith: Thanks for the advice, I'm currently scanning Ebay for a nice vacuum gauge. My pump had its oil changed just before I got it, but I was also given a bottle of the correct oil, about ~500mL. The oil in the pump looks crystal clear through the viewport.
@ Daedronus: That's an awesome looking set up you have there! I love the look of your electrical feedthrough, could you share any specifics?
@ Proud Mary: Thanks for the inspiration, I'll have to do some reading and decide on a good first project.
@ EVR: Haha, sounds like a monster. The only other time I've heard the golf ball analogy was in reference to something far different... ;)
Registered Member #4074
Joined: Mon Aug 29 2011, 06:58AM
Location: Australia
Posts: 335
Very nice. I may attempt something similar if I end up using an insulating base.
Finished the main valve assembly. The chrome-plated valve in the middle isolates the pump from the chamber, while the brass coloured valves are vents for the pump side and the chamber side. I used a thick layer of teflon tape on the brass threads and made sure they were tight, then wrapped self fusing silicon tape around the connections just for aesthetics:
I'm now working on the base plate for my micro-scale jam jar chamber and the hose connections to join everything together. :)
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
if one were to use a vacuum pump to draw oil or epoxy into caps and transformers, what approximate vaccuum micron should one be looking for?
id really like to wind my own ferrite transformers for HV purposes. Without oil or epoxy its just impossible to make a decent attempt.
i find this interesting:
NPT pipe is not really suited for vacuum work, as the threads are not 100% and have a taper, teflon tape really starts to outgas below 100 microns, I found that you can make short term vacuum systems that work very well with NPT and lots of Teflon tape, but for keeping a stable pressure for more then a day you need to braze or silver solder the NPT fittings. Ordinary 60/40 solder has proven to leak and outgas a lot. Incidentally, Harris #56 "Safety-Silv" Braze, although it's made of many materials that like to outgas, seems to do very well for vacuum work on copper, steel and brass. I use the Harris "black" flux on brass and copper to stainless steel, and the "white" flux on stainless to stainless joints.
from:
the problem is if you get hot enough to solder or braze, the the plastic ball seats in common valves melt... so its back to the expensive proper valves i guess.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Patrick wrote ...
if one were to use a vacuum pump to draw oil or epoxy into caps and transformers, what approximate vaccuum micron should one be looking for?
the problem is if you get hot enough to solder or braze, the the plastic ball seats in common valves melt... so its back to the expensive proper valves i guess.
Any foreline/roughing pump (or refrigeration pump) should be ok for vacuum impregnation. (You basically just wait until the bubbles stop (at least, in the coil winding factory I worked in for a while, that's all they did. They did supply Raytheon, though.)
The valves can be stripped and the seals replaced. They are generally known as 'Worcester valves'. Different types of seals are available. I once stripped and rebuilt hundreds in a Nescafe instant coffee plant (cleaning the coffee off the balls was the biggest problem).
]worcester_valves.pdf[/file]
"The range of Worcester Controls’ seat materials is unmatched and includes Buna, Neoprene, TFE, Reinforced TFE, Polyfill, Lubetal™, High-per Fill and UHMWPE"
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Vacuum Pumps - I need an education
