Proper regulator and valve?

[steve_rb]

Already ordered my Cylindrical pyrex Fusor chamber . Diameter is about 30 Cm and hight also is about 30 cm. Ion source is a 8 cm diameter by 20 cm hight copper cylinder with some holes around it for ion extraction. Target also is cylindrical and is about 6-7 cm from ion source wall. ion source volume is about 500 cm^2. Operating pressure will be around a few millitorr. Already borrowed a large hydrogen cylinder for my tests. gas pressure inside the cylinder is 120 bar. I need a proper regulator and valve to feed the gas inside ion source and start plasma. With operating of a few millitorr I need very little gas flow. I had a look into Swagelok site and there are diffrerent varity regulators and bleeding and needle valves.

I need some advice in selecting proper regulator to reduce pressure from 120 Bar to a proper pressure and need to select proper valves to install after regolator to feed a very low gas flow inside ion source to achive operating pressure. which regolator and valves are more suitable?

[John Futter]

Steve
judging by the views and lack of replies
people are directing you to the forum archives

this has been covered before

search, read, and then ask ??s ( if it hasn't already been covered)

[lutzhoffman]

Steve:

I would look on ebay, high pressure lab type of H2 regulators are very common. These will get you to a more managable 5-50 PSI, then you can add another generic pressure regulator, or even a leak based system. Watch H2 though it will leak from the smallest of openings and cracks, everything has to be sealed right.

[Tyler Christensen]

My current preference is to use a laser drilled orifice (5-10 microns) after the pressure regulator to control the flow rate of gas. Then the only setting is the high pressure regulator knob, it makes operation easier and also it seemed to me to be far more stable than even the finest needle valve.

[Doug Coulter]

I like the orifice idea myself -- once you have it dialed in it should be best. The downsides of the SS capillary tubing I use are that if it gets clogged - forget it, replace it. I'd bet an orifice is cleanable in that case.

The upside of the cap tubing is that you can fool with the length to dial it in without having to buy more sizes. If there's too much flow, cut the next piece a bit longer and so forth.

All of the needle valves I've messed with are basically crap. I have a "pretty good one" in there, but after every adjustment of that to set basic flow range (usually quite near complete shutoff) I then have to mess with the much slower responding regulator to get back in the range. This even with very minimal volume between the regulator and the rest -- 1/16" id tubing only a few inches long. Going up in pressure is quick, going down takes awhile.

For various reasons I'm trying to get operation with the absolute minimum gas flow possible, bordering on a sealed off system. One of the ideas there (besides simply saving money on gas) is to let enough reaction products build up to see them on a mass spectrometer. If you are constantly washing the system with gas, you will never see that. We think that we may have, once, after a particularly long and stable run, but would love to be able to be sure and see it every time -- along with perhaps some hotter neutrons if any of the reaction products get involved in further reactions.
Perhaps a vain hope, but it's one of the things we are trying to do here.

[steve_rb]

I think H2 mass flow controllers are best choice. Some are calibrated for ccm or sccm which looking good. Besides the problem of how getting my hands on one of them I think they are the best choice in terms of having precise control over the amount of gas inlet. Other methods may work in terms of getting low flows but precise control is something different.

[John Futter]

Steve
using a MFC is not what you want to be doing
one HV flashover and your MFC will be dead ( unless you are an expert in EMC /EMP)
Tyler and Doug have given the clues
"Listen"
IMHO MFC's pass too much fuel gas --ie waste even the low SCCM ones

work it out our 3MV accelerator has around 5 litres of D2 stored in the terminal @ STM and this lasts many hundreds of hours @ around 1uA of beam current.
start with the KISS (keep it simple stupid) principle. Otherwise you will be spending too many hours trouble shooting things around the outside of the main goal.

[Richard Hull]

John has it right. MFC's are not the way to precision control gas flow to a fusor. We have discussed this at length in a past post session a while back. Like the muon bit, this keeps bobing back to the surface.

Richard Hull

[Doug Coulter]

Yes, I keep looking into these and keep getting the same negative result. The lowest I've found is in the ~1 sccm range -- far too high for our uses unless we just want to pump a lotta gas through a system. I don't -- I'm interested in looking at reaction products post-run on a mass spectrometer and things like that so I don't want them washed down the pump.

Mass flow controllers are great for high pressure/high flow things like perhaps reactive sputtering. That's not where we want fusors to be running at all!

For those not so experienced at running a vacuum system -- remember this, it's important to keep in mind at all times.

1 cc at STP is....10^5 cc's at 1e-2 millibar. Yup, 100,000 to one expansion -- 1 cc becomes 100 liters.

One might do something interesting with a very small automotive fuel injector at a very low duty cycle, feeding a reservoir that is about at atmospheric pressure from say a 2 psi source, then do the orifice or capillary thing after that -- it could give you better regulation than a normal regulator does perhaps, if there was a gage on the reservoir (which might be only a CC or so) and a feedback loop. If it didn't leak across it's valve or someplace else, that is.

However, once I bit the bullet and got a very nice 2 stage regulator from Matheson (ouch$) -- I forgot all about it.

For me, a big issue is control over purity (contaminants should be added deliberately if wanted). This means that basically all the outside of the tank plumbing wants to be at STP or higher pressure, so any leaks are "out". Far too easy for a leak to come in if you have a lot of plumbing below atmospheric and you not know why things are acting funny this time. It doesn't take much of a leak to really spoil purity of the gas at our low flow rates.

I can easily measure the permeation rate of air through silicone or teflon tubing even when it's at 2 psi above atmosphere on my mass spec -- air is leaking in against higher D pressure! D is no doubt leaking out of the tubing at a somewhat greater rate than that -- osmosis, diffusion, call it what you want. Pinching off the tubing right at the tank stops it. Pinching it off halfway cuts it in half...it's just leaking right through the tubing walls all along the length.

Richard's suggestion of all-metal plumbing was on the mark. Really, on the X in the middle of the bullseye. My particular lashup doesn't allow all metal (the gas is fed to my ion source at high voltage potential) but I'm even looking replacing the 6" of 1/16" id tubing I use as an insulator with something like quartz or pyrex and epoxy (Hysol).

Just that little piece of tubing raises my base tank pressure from e-9 millibar or so to e-6 mbar or thereabouts, and that's with a 2" piece of .005" id SS capillary tubing between it and the tank. And the rise is all just plain old air -- not some weird plastic component evaporating into the vacuum.
(as Lesker says, once you have an RGA or a mass spec, you'll never want to be without it)

Disgusting. This is with a 512 l/s turbo...no tubing I've tried, and I've tried a wide range of types -- doesn't have this problem. Copper seems pretty good.

[steve_rb]

Matheson has a ultra pure two stage regulators (9460 and 9470) which seems is best for fusor applications. Difference between 9460 and 9470 is some parts inside are special alloys. delivery pressure is 0-60 psig. which one is better to be used with D2?

Materials of Construction
Model 9460 Series Model 9470 Series
Gauges: 316L stainless steel 316L stainless steel
Body: 316L stainless steel 316L stainless steel
Bonnets: Nickel plated brass Nickel plated brass
Diaphragms: 316 stainless steel Hastelloy C-22
Seats: Kel-F 81 Kel-F 81
Linkages: 316 stainless steel Hastelloy C-22
Springs: 316 stainless steel Hastelloy C-22
Seals: Metal to metal Metal to metal

Also here there is an Apex 0.5 ccm MFC:
http://store.schoonoverinc.com/apexmfc05sccm.html

Also here there is a new full scale 0-0.5 ccm MFC which looks suitable for our purposes:
http://alicatscientific.com/products/ga ... roller.php

[Doug Coulter]

The one I got has "3120 series" stamped on it, and regulates from 0 absolute(!) to 60 psia. I tossed the paperwork, so I don't recall the matheson part number -- they don't make these, they resell someones.
It's more than plenty, I remember getting the lower flow version of the two they recommended. And it will still flow far more than needed, enough to be dangerous if a fitting comes loose and it's set for a couple psi above atmosphere.

Make sure any mass flow controller you get is rated for hydrogen/deuterium -- it matters a great deal.
It won't perhaps be all you need, but it may help if you hook it up to the right sort of feedback loop for your application. Most of us use some kind of restriction (orifice or capillary tube) and a variable gas pressure and get by fine with that.

We are really not here to do all the science and engineering homework for others -- this is supposed to be *collaboration*, not a one way street of information -- *everyone* is supposed to contribute, not just ask for others to. It's beginning to sound like you're a project purchasing manager in need of a scientist or engineer to actually do the project -- so maybe acquiring one of those should be an early priority if you won't become one yourself. I don't mean this to sound as nasty as it might be taken...but really, we all had to do this ourselves, we all made and will make mistakes ongoing and that's just the way it is.

I don't recall your offer to give us all the credit if your thing works, except for the bolt tightening, you seem to be asking us to do all the work for you. People here are nice guys, but there's a limit to how much one-way help we can afford to give -- we have our own projects too that demand our time.

And rather than starting big, consider crawling before walking before running -- you'll save yourself time and money in the long run getting a good feel for how all this works before getting into the big and expensive stuff. And after all, there are several companies that will happily sell you a complete neutron source of 10e9 or greater all done up and finished if that's all you want and don't care about efficiency and so on, and you'd probably save money and certainly time just contacting one of them and buying their thing.

[steve_rb]

Doug Coulter wrote:
> We are really not here to do all the science and engineering homework for others -- this is supposed to be *collaboration*, not a one way street of information -- *everyone* is supposed to contribute, not just ask for others to.

Yes you are absolutly right. This is not a one way street but my car has problem and can't be turned on. As soon as I turn it on I will join other cars and will drive as others and can contribute then. Any contribution now may mislead newbees.


>It's beginning to sound like you're a project purchasing manager in need of a scientist or engineer to actually do the project -- so maybe acquiring one of those should be an early priority if you won't become one yourself. I don't mean this to sound as nasty as it might be taken...but really, we all had to do this ourselves, we all made and will make mistakes ongoing and that's just the way it is.

I asure you it is not. I am not a project purchasing manager. Long time ago I decide to make a fusor but because I had no money and no equipment couldn't do anything. After a few years I find this forum and some money to spend. Decided to start with my own design but I though the best way is trelying on others publications as start point. Then looked for pubs and found Berkely team fusor which looked to me simple and effective. since them I am trying to build their design. Already purchsed required equipments (thanks to ebay) and chamber is about to be ordered but any mistake for me means end of the project since I have no money left to suport the project. That is why I have to be %200 sure of anything I am purchsing.



> I don't recall your offer to give us all the credit if your thing works, except for the bolt tightening, you seem to be asking us to do all the work for you. People here are nice guys, but there's a limit to how much one-way help we can afford to give -- we have our own projects too that demand our time.

Of course I will give you guys all the credit. I am not gaining credit . I only want this thing to be build correctly for my own sake. I have grown in a way that can't tollorate failiar. I wish I knew stuff you guys know and I would be happy to help anyone who need my help.

> And rather than starting big, consider crawling before walking before running -- you'll save yourself time and money in the long run getting a good feel for how all this works before getting into the big and expensive stuff.

Yes I know crawling must come first but I am one of those one in a million who whants to run before crawling and walking. This is a negative point and I belive it or not I am suffering more than any one else from this habit but couldn't change it. I tried a lot and I have lost a lot of opertunities because of this bad habit.

>And after all, there are several companies that will happily sell you a complete neutron source of 10e9 or greater all done up and finished if that's all you want and don't care about efficiency and so on, and you'd probably save money and certainly time just contacting one of them and buying their thing.

Of course this is not I want. I know it can be purchased from a lot of companies but doing ourselves is something that I want since after building first working prototype times will come for trying my own ideas and that is when the fun begins.

[DaveC]

I'm just catching up on the idea flow, here, but to Doug's plaint about the capillary tubing raising base pressures, I am wondering about what bake-out it might have had.

Because of the small diameter, it will take a bit longer for the centermost part of the tubing to reach equilibrium pressure (concentration?). Also, if I remember the outgassing data for SS, it requires red heat or more and hours to fully degas it. So, possibly it just isn't completely clean.

And I agree completely with his view that once you've had an RGA or Mass Spec. on your system, you feel blind without one after that.

To Steve, responding to a later point in this discussion. (Pardon the sequence warping, please)....

I interpret Doug's comment about 'designing the fusor it for you', to suggest that a very enlightening approach is to sit down and try to design what you are attempting to build. Design, however, seems to mean different things to different people. To me, it means, determining pump capacity based on vacuum system engineering theory... outgassing, surface area, target pressures, piping lengths, and zeroing in on a plausible pump size. Then, after taking a deep breath and looking at what these things can cost, iterating on the design parameters a few more times to get something I can actually afford.

Then it's repeat this process with the power supply, the controls and etc.

It DOES take a lot of time, but you will get an engineering/physics/mechanics education, that you cannot likely obtain in an undergraduate curriculum in most schools. And, if you are still in high school, you come out with an enormous technical academic/technical advantage when it comes time to select a school to attend. Further with some Science Fair kudos in your possesion, you are very probably a most interesting candidate to the Admssions Committee, whatever the school financial situation may be.

So, hang in there Steve, this crew will be glad to help you, but you'll do the heavy lifting. We'll try to tell you which corner to start with, and how you're doing it wrong...We're real good at the latter.... hehehe...

Dave Cooper