Use of Swagelok needle valves

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Richard Hull
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Re: Use of Swagelok needle valves

Post by Richard Hull » Mon Mar 19, 2018 5:39 am

Bob is correct. From about 1998-2000 I tended to use very little D2. I mostly did fusion in the 5 micron range and rarely got over 100,000 n/s. It was very easily detectable, of course. With fusor III I found that pressures in 6 inch chambers tend to be in the 10-20 micron range if you want to attack the mega-neutron mark. It wasn't until fusor IV that I hit and passed the mega mark at about 43 kv applied and at 16 microns of flowing D2.

Richard Hull
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Fusion is the energy of the future....and it always will be
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Dan Knapp
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Re: Use of Swagelok needle valves

Post by Dan Knapp » Mon Mar 19, 2018 12:11 pm

Richard,
What current do you run at 43 kV, 16 mTorr?
Do you know what your volume flow rate of deuterium is? I’m having trouble with my system of being able to throttle the gate valve enough to get good pressure control without having very large deuterium consumption (empties a 70 cc buffer volume at 900 Torr in a couple of minutes). My gate valve (VAT ISO 100 over a Varian V301 turbo pump) even when fully closed, but without the O-ring compressed still has a very high pumping rate. If I fully seal the gate valve I can only adjust pressure up, so I can’t really control it. I tried installing a switch on the controller to run the turbo at low speed, but that still didn’t solve the problem. I just installed a 1/8” SS tubing bypass around the gate valve with a shutoff valve and fine metering valve to enable fine control of a low pumping rate, but haven’t had a chance to try it yet. I’ll post a note on the results.

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Re: Use of Swagelok needle valves

Post by Scott Moroch » Mon Mar 19, 2018 5:59 pm

Jackson,

If you have actually acquired Helium-3 gas and are working towards the D+3He reaction, my suggestion would be to use two 0-10 sccm Mass Flow Controllers (as some have suggested). Operating with two gases in a fusor will be hard without the proper gas flow control, especially when one of the gases is as rare and valuable as Helium-3.

Also, on another note, please keep in mind that if you are pursuing the D+3He reaction you will need to operate at around 80-100kV (to reach the peak of the reaction cross section), and will need a charged particle detector for proton detection (one such detector is a Passivated Implanted Planar Silicon Detector).

Best of Luck.

Scott Moroch
"In the middle of difficulty lies opportunity"
-Albert Einstein

Jackson Oswalt
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Re: Use of Swagelok needle valves

Post by Jackson Oswalt » Tue Mar 20, 2018 1:36 am

Thanks for the advice. Since I've got a small fusor (5-way cross), I plan to use alumina tubing to coat the walls in order to increase the amount of HV it can handle if necessary.

As for the MFC's, would either of these work?:

1. https://www.ebay.com/itm/Tylan-FC-280S- ... 1438.l2649

2. https://www.ebay.com/itm/Sierra-Instrum ... 1438.l2649

Thanks!

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Re: Use of Swagelok needle valves

Post by Jerry Biehler » Tue Mar 20, 2018 1:48 am

Either will work

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Rich Feldman
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Re: Use of Swagelok needle valves

Post by Rich Feldman » Tue Mar 20, 2018 3:06 am

One of those links shows a controller with full scale range of 10 sccm for N2 gas.

Other gases need correction factors, such as those given (approximately) in this reference: https://www.mksinst.com/docs/ur/MFCGasCorrection.aspx
Appears to depend on gas density and specific heat.
1.45 for He (very low density, very high CP) and 1.39 for Ar (high density, low CP).
0.36 for propane, with high density and high CP.
Left as an exercise: figure out which values mean more flow, and which mean less flow.

For both H2 and D2, the listed mass flow correction factors are very close to 1.
That means a nominal 10 sccm MFC, flat out, would deliver about 140 sccm of H2 or 70 sccm of D2.
If its control valve can open wide enough. Volume flow through an orifice goes up only as the inverse square root of molecular weight.

Always double-check any advice found on the Internet. I have never operated a MFC.

p.s. One of the links is a MFC calibrated for BCl3, for which the listed correction factor is 0.41.
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Re: Use of Swagelok needle valves

Post by Tom McCarthy » Tue Mar 20, 2018 1:12 pm

Always make sure you can get a datasheet or manual for an MFC (or any other equipment too) before purchasing. Having an official pinout and explanation of everything makes life far easier.

I bought an old MFC and it's just left lying around at the minute. Perfectly suitable, but very little information available on it which makes it nearly impossible to use.

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Re: Use of Swagelok needle valves

Post by Richard Hull » Tue Mar 20, 2018 2:31 pm

Dan, I run about 13-16 ma current at best fusion numbers. I have no idea about my flow rate and consider it unimportant to my fusor operation. The thinking is what works, works and what doesn't, doesn't. It's an art.

Note that not all gate valves truly close in the sense that they will hold 10e-6 vacuums with no pumping. Some will not allow fine control near shut off. Some even have a small hole in the plate!

I do not know about your gate valve. This is why I refused to use either of my two gate valves and opt for a common, manual bellows valve on 2.75" conflats to control my vacuum to the fusor chamber.

At full fusion, I will empty a 2000 torr PSIG, pressurized CO2 cartridge in about 5-10 minutes of full bore running near 1 million neuts/sec.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Re: Use of Swagelok needle valves

Post by Dan Knapp » Tue Mar 20, 2018 11:56 pm

My gate valve problem was that it sealed too well when fully closed and clamped down. When only closed but without the o-ring compressed, it still had an excessive pumping rate, even running the turbo at low speed. I tested my gate valve bypass today and found that the conductance of the 1/8" SS tubing was too low to even keep up with the system leaks. With the gate valve fully closed and the bypass fully open, the pumping through the bypass did not keep up with the system leakage, i.e. the pressure continued to rise. I will add larger tubing. Your use of a bellows valve sounds like the best bet in this application.
Last edited by Dan Knapp on Wed Mar 21, 2018 1:50 am, edited 1 time in total.

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Richard Hull
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Re: Use of Swagelok needle valves

Post by Richard Hull » Wed Mar 21, 2018 3:42 am

A large diameter gate valve plate with o ring, when almost shut and lightly pressing the o ring still represents a rather huge leak volume flow rate against a Turbo. I think a nice large professional gate valve is not the thing for a fusor vacuum system. I almost used my smallest 4 inch gate valve on fusor IV back in 2004. Thank goodness I bought the three reconditioned Varian manual conflat valves from Duniway. They cost me a kilobuck, but they were the right items at the right time.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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