Wanted: turbo molecular pump and controller - Page 1
Forum section: electronics / general

author: TerraHertz
author_rank: Super Contributor
timestamp: December 24, 2014, 02:21:06 pm
content: These are high vacuum pumps, that work by magnetically levitating a turbine and spinning it really, really fast.For some reason pumps and matching controllers virtually never seem to come up together on ebay, which is odd since either part is utterly useless without the other.Another problem is that these pumps are delicate, so I don't like the idea of trying to ship from overseas.Perhaps someone in Australia may know of where I could find one here? (Sydney Oz.) Needs to be cheap too.Which I know is an unlikely combination. Just thought I'd ask.

author: Lightages
author_rank: Unknown
timestamp: December 24, 2014, 06:35:08 pm
content: Is there a specific reason you need a turbopump? Most of the same things can be done using an oil diffusion pump, that is unless your process is very to sensitive to possible oil contamination. Most of any problems with oil contamination can be eliminated with a water cooled chevron in front of the pump but this also limits the pumping speed.I would most certainly NOT trust any turbo pump from ebay unless the seller had a 100% feedback. I would not worry about shipping a turbo as they are shipped all the time from the manufacturer.

author: wiss
author_rank: Frequent Contributor
timestamp: December 24, 2014, 07:28:44 pm
content: The downside with diffusion-pumps is that they do not tolerate "high" pressure, as in a pvd-chamber. But they tend to pump very large volumes at lower pressure (below 0.1 mBar or so). Diffusion pumps could probably be had very cheap but good pump-oil will cost more (~1000€ per litre for polyphenylether). Polyphenylether will not burst into flames if subjected to atmosphere (= good).

author: Lightages
author_rank: Unknown
timestamp: December 24, 2014, 08:34:16 pm
content: Of course different pumps have different benefits. The beauty of a diffusion pump is that it has no moving parts. Unless it is completely abused they are hard to damage, especially in transport.The ideal system for the cleanest system is a mechanical backed turbo with a cryo pump helping out. The problem? Expensive and easy to damage the turbo and cryo if proper procedures are not followed.The simplest and easiest to maintain is still a mechanical back diffusion pump, IMHO. I would never design a modern system with one but for a casual use hobbyist it is the easiest.

author: TerraHertz
author_rank: Super Contributor
timestamp: December 25, 2014, 03:54:21 am
content: I asked because I'm currently putting some more work into a long-running (ie very slow) project. See pic.Fairly large vacuum chamber, for which I already have a humungous-big oil diffusion pump, and good mechanical pumps - not seen in photo, they are going in that empty black rack at left. The main one as soon as the paint is dry on the mounting frame. Day after tomorrow (the enamel takes ages to harden up.)I know about using a cooled baffle to keep down oil backstreaming. There's space in this system for a baffle, if I run the oil diffusion pump. Also planning to have a variable iris aperture between the chamber and the cold-trap/diffusion/turbo, to regulate flow impedance.There's a range of different things I want to do with this setup. With some of them, any oil vapor backstream at all would be a pain. Also watercooling will be a pain too, since there's no water plumbing in this room. I can knock holes in a wall and put a recirculating heat exchanger outside if I have to, but would rather not.Another factor is wanting a fairly quick cycle time, from chamber open, to operating vacuum, to chamber open, etc. Hot oil would seriously hinder that.At the moment I'm still working out what suitable salvaged and usable vacuum gear I have, to build into that empty rack. The plan is for that rack to be the main vacuum pumping and gas supply rig, with the experimental chamber stand (blue) carrying all the sense/drive gear, as well as the big oil diffusion pump. But I'm *hoping* that diffusion pump won't need to be used as a pump - just sitting there as a bit of static plumbing, and possibly space for a liquid N cold trap in the top, with the oil vanes removed.Hence why I'm looking around for a turbo pump now. Need to plan layout and plumbing, to allow for it if I can find and afford one. I think they are a lot less trouble than oil diffusion pumps.Also, the whole rig will be automated. Hopefully avoiding goofs like bleeding in air while the oil diffusion pump is running hot. Or the hot cathode sensors are operating.I'm sorry I can't be specific about the primary purpose. I do know, but don't wish to discuss. There are a bunch of sideline interests unrelated to the main purpose, for eg studying behavior of medium and low pressure plasma. So the system needs to support a range of operating regimes.Oh and for anyone wondering, yes, that 200KV power supply stack is going to have a full Faraday cage around it. Turning it on as it is now would be death to anyone walking past, and probably a lot of nearby electronics too.

author: SeanB
author_rank: Super Contributor
timestamp: December 25, 2014, 04:14:13 am
content: Building a Bussard fuser then?

author: TerraHertz
author_rank: Super Contributor
timestamp: December 25, 2014, 05:12:55 am
content: Quote from: SeanB on December 25, 2014, 04:14:13 amHa ha ha. No. None of the above. (All the other types you're thinking of too.)Though, I might as well do the standard Fusor thing as one of the incidental fun projects along the way. For the heck of it, since the gear is so well suited.

author: SeanB
author_rank: Super Contributor
timestamp: December 25, 2014, 05:19:32 am
content: Quick way to plasma clean the chamber though, so you can do the ion deposition or microscope work.

author: TerraHertz
author_rank: Super Contributor
timestamp: December 29, 2014, 07:38:15 pm
content: Project update:http://everist.org/NobLog/20141212_racked_serendipity.htm

author: SeanB
author_rank: Super Contributor
timestamp: December 29, 2014, 08:23:01 pm
content: Very interesting there. Read the associated article about railings as well, and can give you a tip for next time. Take steel end cap and drill hole for rod through it ( plain cap) and weld with about 10cm sticking through with a sharpish end. Then weld a small amount of heavy wire, or just weld a long droopy bead around the bar to make it rough. Drill the hole to fit the long stud, and use a chemical anchor of appropriate size, or failing that drill the hole to be 2-3mm diameter larger and clean it out thoroughly of all dust ( or at least a lot of it) and then use some slow curing ABE Epidermix ( or some Sika Pro HP urethane sealer) to fill the hole partly, then push the rod in and hold by some method ( I just use a temporary clamp drilled to the wall) for the cure time. Clean up the stuff squeezed out before it cures ( otherwise you will need an angle grinder and care with grinding disks) with a cloth and turps. To remove you break the wall in most cases, or break out the bricks around it.

author: Fluxed Matter
author_rank: Regular Contributor
timestamp: December 29, 2014, 08:47:21 pm
content: What range of vacuum are you looking for? If you want good vacuum, like ultra high vacuum(UHV) then I would suggest a cryo pump. Once a cryo pump has been regenerated it will run for quite a while. Also the chamber can be vented and put back under high vacuum in a matter of minutes. Back the cryo pump with a dry pump and the system is virtually maintenance free.Depending on the pressure you are want to achieve in the chamber during you experiments you may just need some mass flow controllers to get low process pressures. For controlling at a higher pressure I would suggest a gate valve with the ability to throttle pressure for your experiments. Hope this helps some. I work on this stuff everyday so if there is anything else you like to know please don't hesitate to ask.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 29, 2014, 09:52:45 pm
content: I want to say, anything over 50 or 100kV in vacuum needs to be registered with the local nuclear regulation authorities since it's, well, dangerous obviously -- hard x-rays, some lower energy nuclear reactions (I think it's p + 18F has a resonance in the 100s keV?). So, keeping it under 30kV in vacuum would indeed be a good idea, for more than a few reasons.Whatever it is you're doing... neat.What I'm more curious about right now... how the hell do they need so many transistors on that thing?! It's only 200W, even if it's a class A amplifier, I just don't get it!Tim

author: Someone
author_rank: Super Contributor
timestamp: December 29, 2014, 11:04:49 pm
content: Quote from: T3sl4co1l on December 29, 2014, 09:52:45 pmDealing with the Australian regulatory agencies is a massive pain, NSW shunt it off to a branch of their environmental protection agency.http://www.epa.nsw.gov.au/radiation/index.htm

author: TerraHertz
author_rank: Super Contributor
timestamp: December 30, 2014, 01:59:21 pm
content: Quote from: Fluxed Matter on December 29, 2014, 08:47:21 pmActually for the main objective, only pressures measured in % of 1 atm, not so much negative powers. For which the plain mechanical pumps will be good enough.But you know, once you have a vacuum chamber then it becomes a challenge to see how low you can go. And I do want to play with some other things... vacuum silvering, various 'electron tube' type things up to microwave frequencies... and I'm sure more things will suggest themselves. It's a hobby, not a commercial proposition.QuoteHmm... by cryo pump you mean cold trap? I'm planning on including a liquid nitrogen trap for when I do try for pressures below 10-6 Torr. But its all on a shoestring, and buying liquid nitrogen is to be avoided if possible. I do have a large storage dewar though.I don't know what you mean by dry pump. Roots pump? (Ah, google says yes.)A Varian Helium Leak measurement system that's to be part of the system includes a cryo trap and small oil diffusion pump. See pic. It needs work, for instance replacing all the pneumatics tubing.I'll be able to use it as a pumping system to (slowly) reach high vacuum, assuming the chamber isn't too leaky/absorbent. The main purpose of that machine is to see if I can modify the He4 mass spectrometer to be scanable, at least for a few atomic masses either side. As yet unknown if possible.Even if not, it's still the best way to find leaks.QuoteThe initial plan is pulsed-leak valves for gas input, and a home-made iris valve between the chamber and pumping system for outlet rate control. The iris I can drive with a small stepper motor. I hope to avoid manual valves, since I want to have the entire sequence automated.I do have a large manual gate-like valve that fits the bottom port of the chamber.QuoteAppreciated. It's a pity (for me) that you're in the USA.The main attraction for me of a turbo pump is that they seem to be very low maintenance, have no consumables, and last virtually forever if not mistreated. Also clean, and fairly high rate. Futzing around with expensive, spillable, and potentially poisonous vacuum oils for diffusion pumps, etc, is something I'll avoid if at all possible.Quote from: T3sl4co1l on December 29, 2014, 09:52:45 pmExactly. I don't know which is worse, ionizing radiation or red tape. I think I'll just avoid both.QuoteI promise I'll add the scanned schematics fairly soon. Just a few more urgent chores, like getting my NAS resuscitated after the lightning strike.Quote from: Someone on December 29, 2014, 11:04:49 pmI can imagine. It would not surprise me if Fusor type experiments would be flat out illegal in Australia, so I'm glad that's not what I want to do.Another thing I had in mind to try for fun was making large versions of those 'plasma ball' ionization displays. Several decades ago I saw a few of those that were made by a tech-artist in the USA, on exhibition at the Powerhouse museum. These serious ones were totally unlike the feeble things you used to be able to buy. They were about a meter in diameter and made with careful mixes of rare gases, not just air or nitrogen pumped down. The results were stunningly beautiful, each one completely different in character. Sorry I don't know his name.But I'm told these things are now illegal (due to X-ray generation), so that's out.