Diff pump

[Jgn1]

Hello there!

Is it mandatory to get an air-cooled Diff pump? Isn't a good idea to use water cooled ones? Which are the equivalent to the Welch, Edwards, Precision for the diff pumps?

Juan

[Jerry Biehler]

Air cooled is more convenient. Water cooled works better for things that are buried in a cabinet with no air or temperature and vibration equipment around them. Like electron microscopes. If you have a source of water or a recirculating cooler with enough pressure (~45psi) go for it.

All the major manufacturers make DP's. Edwards, Varian, etc.

Though with the recent dumping of cheap turbo pumps on ebay and home brew controllers here a few are skipping DPs.

[Jgn1]

Thanks for the reply Jerry!

Well I have these two options:

http://www.ebay.co.uk/itm/EDWARDS-EXT70 ... 4292wt_758

This is a lot of money. Is this a very good price? Is it worth to make an ultra effort to get the money? Besides the Fusor I would like to perform many other experiments.

Does a Turbomolecular pump works? For example:

http://www.ebay.co.uk/itm/Balzers-Pfeif ... 500wt_1006

Same questions as 1.

[Jeff Robertson]

Hey Juan,

I would definitely recommend a diffusion pump over a turbo pump. They both serve the same purpose, but a diffusion pump is many times cheaper and (in my opinion) easier to maintain. Occasionally you can get a diff pump on ebay for under $100, while it's almost guaranteed to find a couple of them $100-200.

I use a water cooled diffusion pump in my fusor. It is a little more effort to rig a water cooling system, as opposed to an air one, but that shouldn't scare you away from it if you find a good deal or something. My pump had the spiral tubing around the diffusion pump (for the water cooling system) already in place, so I just bought some plastic tubing from Home Depot and an aquarium water pump from Petco (hah!). I just have the pump and the ends of the tubing in a large bucket of water, and it runs beautifully.

But yeah, I personally never saw the point in a turbopump unless you already have one lying around.

Jeff

[Jgn1]

Thanks for reply Jeff!

hmm, I see. So what's the point of a Turbopump then?

I found this diff pump on Ebay Germany. You think this would work ok?

http://www.ebay.de/itm/Quecksilber-Diff ... _527wt_991

Could you upload or send me a pic of your diff pump set up?

About the Turbopump. 900 pounds still very expensive for that, right?

[Rich Feldman]

Wow, that glass mercury-vapor diffusion pump is a classic.
If I lived in Germany, would bid on it, just as a collectible gadget.
I'm not afraid of boiling Hg, nor am I cavalier about its hazards.

Perhaps it will work with modern diffusion-pump fluid, instead of mercury.
Our vacuum experts may know whether the heater or nozzles need to be changed.

Rich

p.s. Haste will cost you money.
Not having a deadline, I eventually acquired an air-coiled oil diff pump with fan & throttle valve for $75. And a Tribodyn self-contained turbo-drag system (incl drive electronics & backing pumps) $300. Looks just like http://www.pchemlabs.com/product.asp?pid=1079

[Jgn1]

These are the spec. given by the seller:

"a 3 stage mercury diffusion pump that reaches a high vacuum of 1.3E-6 mbar at a pump rate of 360l/min. It has tobe supplied with 220V/50Hz and 500W. A backing pump is needed, that is able to pump down to 20mbar via the NS14 ground glass joint. The High vacuum side is connected by a NS29 joint."

"The pump is used but in good condition."

Juan

[Jerry Biehler]

Turbo has a lot of advantages. One is pump down speed. You turn it on and spend up within a minute or two and is going. A DP has to warm up. Even the small one on my friends SEM takes about 20 minutes to warm up, same for the 6" in my deposition system.

Turbo pump is short for turbomolecular pump. There is also a Turbo-drag pump which is a subcategory. They allow for higher fore line pressures so you can run them from diaphragm pumps.

This may not seem like much of a deal, but if you are opening the chamber a lot it can save you the hassle of installing isolation valving around the DP so you can work on it and then pump back down.

One other thing about newer turbos is you can slow them down to throttle them. This will save you on D2.

Also DP's back stream without a cold trap. This means some of the oil vapor works it way back through the system.

But DP's a pretty indestructible. If you let a turbo up to pressure while it is still running it is probably going to be toast.

That being said, I will keep using turbos in the future. They are very reasonably price on ebay used.

That first pump with the complete setup is really nice. Complete dry system. No oils. Actually a pretty good price, I would say. Pretty much the perfect size for a fusor. Wont have to throttle it down as much.

[Tyler Christensen]

A lot of turbo's take forever to turn off, making DP's just as good from a speed perspective. My little NW50 air cooled DP turns off about twice as fast as the little 4.5" turbos I use at work (which clearly don't have magnetic braking). With very careful gas bleeding that can be accelerated to about 1.5x slower for the turbo, but it still takes about 20 minutes. DP cooling can also be accelerated by putting a cold-liquid bath on the bottom.

[Dennis P Brown]

I have both systems - a turbo and diff. pump (oil) - on my accelerator. Both work very well (I do not run them simultaneously.) The diffusion pump gets down to the same vacuum level and is (once it gets to temp) very fast (I do not have a trap.) That said, I always use the turbo. Besides fast operation, no water is running and no cool down issue after shut down (that is important for Diff. Pumps! Otherwise you can crack the oil if any large amount of O2 gets to the hot oil.) By the way, my diff. pump has a special water connector for the hot oil (to rapidly cool) but I never hooked it up - the pump is a backup only. That said, look for one that does (mine is a Edwards) that would be a great time saver!

My turbo has a special inlet for rapid shut down. This works great because as one person pointed out, they take forever to shut down (don't free vent to the air!) My shut down vent is hooked up to a dry air filter and I use this to purge/back fill my system. This allows my accelerator to get under 5*10 -5 torr in under ten minutes after venting to the atmosphere.

I would say that cost wise, a diff. pump is far cheaper and will do the job - both units for a fusor, by the way, will need a main throttling valve/Gate valve on their intake.

Now and then, a turbo is overlooked on e-bay and a good deal can be had. Since that is rare (you need a controller, don't forget - check out Alexi's homemade controller for a very commonly available turbo pump) deals on good diffusion pumps occur all the time. That said, I'd NEVER own a Hg based diff. pump. Those vapors are deadly and without a cold trap, Hg will back stream and contaminate all your lines and the fusor. Then, every time you open the fusor, Hg vapors will leak. Remember, that Hg emits a lot of vapor at room temperature and that 70% of all Hg vapor you breath, is absorbed into the blood stream. Just saying.

Hg is not cheap to buy and must be disposed of legally and that isn't cheap - diff. pump oil is readily available on e-bay and the price is very reasonable (diff. pumps should never be sold with oil in them and if so, you need to get rid of that oil.)

By the way, my diff. pump is water cooled but I have water/drain system in my den (I installed. I really liked how the one person solved that issue using an aquarium water pump - really impressive!)

Your call on what suits your needs and wallet.

By the way, I have bought two outstanding two stage high performance vacuum roughing pumps on e-bay for under $100 for one and under $50 for the other (both these prices included shipping!) Deals on these units occur all the time (the other unit is in storage in the event that my primary fails. I like to backup all major systems.) Don't get me started on the amazing deals the Chinese are giving 24/7 on SS fittings/seals and connectors ... . Always watch e-bay and learn what key words work - the deals can be amazing!


That all said, waiting can be an issue and even then, someone else my out bid you or drive the price up. As Jerry Biehler said, that first unit is a really nice unit for the price. IF I had the money (I don't) I'd really consider that system. A top grade vacuum system (a dry fore pump means no oil trap for the main is needed) that gets down near/to 10-7 torr (and that looks to have a high volume capability) like that can be used for so many applications besides fusors - an deuteron accelerator, or vapor deposition system to name two (the roughing pump could handle any sputtering application.) Again, your call.

[Jgn1]

Thanks for the info!

I manage to get the price down to 950 pounds.

did you read that the XDS10 scroll pump is not included, but only the Turbo pump and controller?

I'm about to confirm it, but I want to be sure that I wont regret it, haha.

[Tyler Christensen]

That's an awful lot of money for a turbo pump on ebay. They frequently come up for under $100 without a controller, which could be purchased separately or pretty easily made yourself if you know anything about electronics. In fact I'm pretty sure there are some <$100 turbos up right now, someone recently posted about them.

I wouldn't even begin to consider spending this much money for an ebay turbo myself.

[Dennis P Brown]

Sorry to hear that the main pump is not included and really, they are not selling the entire system - that makes the deal way over priced. I fully aggree with Tyler - look for pumps on e-bay and pass this one up.

Edit: I would like to add - a turbo (if obtained cheaply is well worth the effort) is nice but what are you aiming for? A fusor that demonstrates all but neutron production or one that produces neutrons? Remember, the primary pump (roughing) and some type of vacuum gauge with a chamber and all connecting vacuum components are the main items you will need to get started. One major issue to consider is what level of power (the HV system determines if it is a neutron producing fusor or not) you are trying for? A turbo or diff. pump are secondary issues compared to all of this and should not eat up most your budget!

The issue is really what are you trying to achieve and the time frame - for instance; buying a chamber (some vacuum SS chamber) is one of your main issues to be addressed. Feed thrus and what and how you will do that is far more important than a turbo pump because as most can tell you here, depending on the approch, that can be a big $$$.

This is purely my two cents but I have been collecting stuff for a fusor but have not tried for a power supply because I have not seen one that I feel is worth the cost/effort/gamble. Of course, I am not trying very hard since I am focused on a linear accel. and production of neutrons (if I am lucky!)

[Jgn1]

Thanks for the advice!

I just want to learn as much as I can. That's the goal. I'm just a student. But eventually, with more experience, I would like to make experiments and also try my own designs, taking optimization into account. I would like to try everything within my reach - I'm also interested in linear accelerators.

I'm currently waiting for my primary pump to come. It's an Edwards (number 5). Two days ago I bought two hemispheres of stainless steel, with a diameter of 25 cm. They were very expensive. I'm still missing the Vacuum gauge and the connecting vacuum components. I plan to do that probably on the weekend.

I still need to read a lot about the "theory" of the fusor. I'm planing to resume my readings also on the weekend - on thurday and friday, I have 4 tests to do at college.

I'm spending all my savings, and I don't care - but that doesn't mean to spend money innecessarily!

I'll go for a DP.

[Dennis P Brown]

I have no where near the experience/knowledge of many of the people here and I am just using what I learned putting together my accelerator project. But for vacuum systems you really need to make some important decisions at the very start or you risk wasting a ton of money – what type of connector system will be used for the vacuum support system? All SS? I had to go that route because I am trying for 10-6 torr (so that regular bottom 10-5 torr is trivial to achieve) but fusors are different - they work in the micron range.

Since fusors do not need levels of vacuum below one micron, both copper and/or thick walled plastic/rubber vacuum grade tubing is fine for many parts. These types of ‘tubing’ systems are hard at times to interface with standard SS flanges/connectors and that is the main issue for people who go that rount. Not impossible to do – my DP fore line to SS quick flange system is a short piece of vacuum grade rubber tubing. Just realize that off standard stuff can kill a project unless you can machine around the issue or put up more cash to interface these components.

Quick flange (use a K for quick; so really KF) connectors are great and the standard 25 mm diameter (KF-25) is perfect for most easy to get items. The Chinese sell the required o-ring and clamps dirt-cheap and I bought a six head 20 mm KF octopus rig for 1/3 the price I saw everywhere else and the workmanship was ultra high quality.

That all said, valves and electrodes are really high end costs that many just overlook at first before laying out their system in detail. These components are critical to have (and think carefully on the vacuum system design; otherwise, you buy stuff that turns out to be of no use!)

It is best to search e-bay and look for deals on these items - I got some great deals on vacuum valves BUT they all had issues and needed work. Otherwise, you waste a lot of funds and end up with expensive scrape! Remember, leak checking is not easy and gross leaks will kill any fusor project. I did much of my building effort dealing with leaks but again, I am at a very high vacuum range.

From what you are saying, I'd think your next major item to watch for and CAREFULLY price it relative to performance before buying it (they list the requirements here in the forum) is a good x-ray transformer. Such a transformer has to be the correct power/voltage or fusion is impossible. Remember, these voltages/currents are lethal and you need to deal with that – you get no second chances. That is why I am hyper fearful/careful of the x-rays that could be produced by my system. The voltages a fusor uses can also produce dangerous fluxes of x-rays, too.

Best of luck and this is really a great forum with really knowledgeable people who have so much working hand skills.

[Jgn1]

Your info is very appreciated!

I really don't know what exactly you refer with "what type of connector system will be used for the vacuum support system?". (Note: I'm quite a newbie.) Do you mean the connectors around the chamber? If yes: yeah, all SS; that's the plan. I would like to use this chamber for other things too, not only for the fusor. What exactly? I don't know, but I think something else can be done. Time will tell.

I'll take note about your suggestions for the flanges. I actually plan to design how they are going to be distributted and plugged into the chamber - the order doesn't matter, right?

I plan to use a TIG welding rod, as the electrode. Is that fine? I have no idea about the valves, only that they are expensive.

I still haven't read anything abouth the X-ray transformer. I plan to read first about it, and then search for it.

[Dennis P Brown]

I am in no way knowledgeable about fusors - do read up here on the forum and ask the experts here.

What I was saying about ‘connecting system’ is how do you plan to connect a roughing pump to the chamber with a vacuum gauge somewhere in between? Also, how to later install a DP/or turbo and this, in turn, then to the chamber? Gate values to throttle? And so many other things like electrical feed thrus.

If you look at my linear accelerator support system, 70% of the volume and 90% of my cost is simply vacuum connection stuff – SS ‘bellow’ lines, valves, clamps, QF elbows, four way KF, and the list does on. Having a roughing pump and chamber are the backbone of a fusor but how these get connected together is the $$$ question. I use quick flanges (KF) because they are simple, can be found every were, are great for low/high vac and most all types of SS flanges feed thru's (electrical both high current or high voltage, vacuum pump ports or accessories, etc) come in versions that use KF. Jut be careful – many off size QF are out there and many cheap flanges/adapters are also off-size; hence they’re cheap. But wait until you price adapters and the savings vanish.

Quick edit: issues about system location. Where will the system be run? Appartment buildings may be very questionable esp. the line power for an x-ray transformer and issues of radiation (x-ray but also neutrons for high end fusors.) Note that my entire accelerator system is installed on a cart to allow placement or removal (but a single 120 outlet handles all my power needs - total system runs under 10 amps. A fusor can be far worse.) With a cart, I had to carefully layout the design ahead of time if I wanted everything to align up and fit in the available space (including for me, heavy shielding.) Just saying that such a minor point is often overlooked but it can kill a project if not considered.

One thing I will warn against just from my experience – this may not apply to you - don't double up uses for the chamber. The fastest way to fail is to try and build two or more systems in the same chamber (Fusor, metal coater, plasma asher or what-ever.) You more often than not waste time, money and get frustrated by minor issues. My two cents but I have built many operating vacuum based systems previously and have learned the hard way.

One final word - avoid jury-rigging any high voltage system to adapt to a chamber. Anything that is high voltage (and carries any real current) should use proper connectors (read proper wire insulation), feed thru’s (made for the voltage/current.) Cutting corners here is asking for electrocution.

[Jgn1]

I'm still figuring out how I'm going to do the connection system. Currently I don't know... No idea.

What's wrong when you make your chamber an hybrid system?

I'll take special care to the hazards. The whole idea is not to create the machine that will kill you!

Quick edit: well, I'm doing all this in my flat - in the kitchen...

[Dennis P Brown]

Again, I am no expert on fusors but when you ask:
"What's wrong when you make your chamber an hybrid system?"

My point is that different applications generally require different feed ins, vacuum connectors, ion guns(s), gauges or viewing ports, etc all in one chamber. Some of these may block space for fusor items and some applications may create contaminates that would cause issues for one or both or all other systems. A lot of unknowns, added to already a complex and possibly dangerous system.

It would make more sense to install a vacuum system with gauge controllers on a movable cart and build a chamber for each application. Any given application, say the fusor, would have its required gauge sensors and high voltage systems already in place. You'd just connect the vacuum system to it. After getting done, roll the vac system to the next chamber/experiement. Again, just my two cents after many, many years of experience with these types of systems.

Late edit: remember, some applications do not require steel chambers (even fusors) and glass and other housing can work depending on what you are trying to do. Most just require an chamber that allows some degree of vacuum.

I did design my system on a cart with wheels so it can also be connected to a fusor that would be in a fixed location a bit away. Many fusors have heavy and very dangerous (ie need proper wiring/shields) electrical systems that are best left in place.

Your call on how best to use your chamber but I'm at a lost on what else a fusor chamber would also work as ... . Your device. your call.

Best of luck.

[Jgn1]

I really like your idea of the table with wheels. I definitely will do that.

Some days ago I saw this (pic atached) plastic (PC) container which is supposed to be a lamp and I bought it. I though that it would be perfect for a Vacuum chamber. You think it's possible to create fussion inside this plastic container? And if I want to put ion guns, no problem?

The other pics correspond to the two hemispheres of SS that I bought.

I'm currently looking for the Vacuum gauge and a controller. Does the Varian 860A controller is ok? If yes, any suggestion for the Gauge?

What's a "CVC Discharge vacuum guage tube cat. no. GPH-001A for high vac". And CVC tubes?

Quick edit: I took the photo with my laptop - I don't have a camera and I don't have a mobile...

[Dennis P Brown]

A real fusor might poses issues with a thin walled plastic globe. Could it withstand 15 psi? If it did, no reason it couldn’t act as a demo with a very low wattage power source to strike a weak plasma (a few ma at 5 keV) but a real fusor? I don't think so.

I think you need to ask this question in the fusor construction section and people who know what they are talking about (not me!) can answer that question.

As for the gauge, repost that so people can answer - I know you need a gauge that can accurately read in the 1 to 50 micron range. But some gauge types have issues with fusors - again, ask the people here in the know about fusors!

Look at my cart (see my first Linear accelerator post in the general section) for ideas. Its a bit large for a fusor stand. To make it I just took a standard work bench, turned it upside down, and added cart wheels to the new base. I then place the wood 'bench' surface on top of the orginal feet of the bench. Installed wood 2x4's to give stronger support to the top and allow me to bolt the top bench to the angle bracket feet of the table. Very simple but very strong. The thick wood top insulates my equipment and as an added bonus, provides a good work area at the same time!

[Brian_Gage]

This question has been answered numerous times. Plastic or glass cannot or should not be used for anything more than a demo plasma chamber.
Also, as mentioned, as fusors go, plastic anywhere will either not withstand the heat or simply contaminate the process.

[Carl Willis]

Juan (and everyone else):

Please help contribute to the site's organization by limiting the discussion in this thread to the original topic about pumps.

A discussion about chambers can be a separate thread.

A general discussion about vacuum system design can be a separate thread.

Also, please respect the one of our four rules that requires you to have a user name of the type [first, last].

Thanks,
Carl

[Jgn1]

Ok, my bad - won't happen again.

Thanks!