Silicone tubing with hose barbs OK to pull low vacuum?

Every fusor and fusion system seems to need a vacuum. This area is for detailed discussion of vacuum systems, materials, gauging, etc. related to fusor or fusion research.
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Dennis P Brown
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Re: Silicone tubing with hose barbs OK to pull low vacuum?

Post by Dennis P Brown » Tue Oct 24, 2017 7:27 pm

Then either the pump has issues, the gauge does or more likely, your connector system is leaking very badly.

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Richard Hull
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Re: Silicone tubing with hose barbs OK to pull low vacuum?

Post by Richard Hull » Wed Oct 25, 2017 12:52 am

This close to the pump, even a 1/4" hole should yank down to well below 100 microns in seconds! (assuming all clamping is good, which it may well not be.) Even a rotten trashed out pump, at the head, sealed well, should sink below a torr!

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Re: Silicone tubing with hose barbs OK to pull low vacuum?

Post by Shireesh Apte » Wed Oct 25, 2017 1:06 am

Thanks Niels, Dan, Dennis,

I put loctite on the fittings and started the pump after the loctite had hardened (approximately 4 hours later). The micron gauge almost immediately read 110 microns (a significant improvement from 1400 microns), but began to creep up so that it was reading about 400 microns a minute later. At this point, I stopped the pump and could distinctly hear the hiss of air ingress. The micron gauge immediately displayed overload.
Hence, I have liberally applied loctite to all the fittings and will start up the pump again tomorrow. I find this highly encouraging as it indicates that the micron gauge and the pump are apparently functioning as intended. If I stop all the leaks, then I should be able to try my 'container store' plasma chamber again, hopefully with a plasma being generated this time.
Once I am confident that I can produce a plasma , and the rotary vane does go below (or hovers at) 100 microns, then I will purchase a diffusion vacuum pump (still costly with >$400 for a rebuilt one on dunway) but I will query ebay as well. I already have a 2.75 4-way SS with 3 conflat flanges adapted to 1/8th inch female NPT. I have ordered 3, 1/8th inch male NPT to KF-25 adapters. I also have a 4th conflat flange view port. I have the necessary hardware, copper gaskets, and 1/4th inch hex bolts and nuts to assemble the fusion chamber. I am going to go with the same design for the high voltage feedthrough as I have for the plasma chamber (please see an earlier post for details)
If the tubing starts to collapse; as suggested I will either put a spring or hard material inside to hold it up or switch to a Teflon or SS tubing. For the fusion part of the project, I aim to switch to SS 1 inch with KF-25 flanges that adapt to whatever tubing I have coming out of the pump/fusor.
Thanks again and I will post pictures again sometime this week. Still a long way to go but getting there slowly but surely.
Best,
Shireesh

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Re: Silicone tubing with hose barbs OK to pull low vacuum?

Post by ian_krase » Wed Oct 25, 2017 6:07 am

I highly suggest searching for diffpumps on ebay, repeatedly, over time -- and also at local surplus stores if they exist where you live. It is *very* hard to ruin a diffpump except by losing the jet chimney from the inside. This is in blatant contrast to every other kind of vacuum pump or vacuum equipment except simple pipe fittings. Of course, repairing one assumes some degree of tools and skills.

I don't know if anybody here, except a few super-experimenters with deep pockets, ever buy anything but pipe fittings new or factory refurbished.


Diff pumps of the size you want on ebay are now somewhat uncommon and sell at a high-ish price -- or periodically sell at a very low price from people who don't know what they are selling or do not care.

As far as connecting your fusor chamber to your diffpump, this is almost always done by directly attaching the fusor to the pump flange (ideally with a valve in between). High vacuum does not like flowing through narrow pipes at all, and your pump is only as good as the smallest diameter aperture.

Since you have a micron gauge (almost certainly some form of "thermocouple gauge") you can try spraying Dust-Off or isopropyl alcohol on your pipe fittings to find the leaks -- this will cause a change in the gauge reading. If you have a plasma running, it will also change the color and appearance of the plasma almost immediately. I also like applying loctite or other sealants while under vacuum.

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Re: Silicone tubing with hose barbs OK to pull low vacuum?

Post by Dennis P Brown » Wed Oct 25, 2017 9:53 am

Hello and welcome to the world of vacuum leak detection/control - seriously, this is an issue that can plague anyone but making matters worse is not the solution here - i.e. using sealants to patch worthless hardware. Until leaks are in the micron class, chemical detection isn't the method - ones ears (as you now know) works best.

Your fittings are beyond useless as you are seeing only too well; so wasting time and effort on "sealing" them isn't worth the trouble because they will continue to fail. Having a decent vacuum pump - while the central purchase and minimum requirement to start on real vacuum work - is a necessity, it isn't sufficient as you have now discovered (no doubt to your aggravation. Many of us have had similar issues so don't get discouraged.)

Relative to getting a diffusion pump (DP), hold off. If a "steal" for a DP appears on ebay, do get it (but remember THREE critical points about those devices: the heater must work, the main opening must be something you have the ability/funds to connect to, and one will need DP oil (it isn't included.)) If you can handle water cooling that is a big plus since there are more of these types of pumps available and often at good prices. Do note what I said to start - only buy one if the price is really good (and they guarantee a working pump or money back w/shipping.) However, you are not ready for high vacuum - you are struggling to still get below a torr! Also, getting below 100 microns (barely) is not acceptable for a DP's health and operation. Your system should get below 10 microns with a good two stage vacuum pump like you have. Until that, your system is leaking too much and oxygen will steadily fry your DP oil.

There is no way around the need for proper vacuum fittings with high vac - zero. That gauge will NOT work (seal) properly with that worthless connection fittings. Get a proper thermal couple (TC) or similar gauge (They can be had for low cost if one is careful.) Richard offers these, I believe.

What you need bare minimum for HV if you are serious about making a real fusor (before a DP is obtained):
1) Your pump and system reaches below 10 micron and leak back rate (a subjective measure here) really shouldn't exceed a micron/second and rapidly slow and plateau so that over a few days, the system will then reach a few torr- that implies your system is tight but undergoing normal out gassing issues.
2) A gauge that measure accurately (below 50 microns and doesn't make connecting to std fittings an issue.)
3) A coupling to your fore pump that converts it to the std vacuum fittings you select for your arrangement.
4) Decide upon your chamber design and be certain you fittings work with what you settle upon.

Remember: a high vac system does not need sealants, or loc-tight, or even vacuum grease (except possibly for o-rings but follow std vac techniques for applying) to hold a good level of vacuum; if one uses those, then something is wrong: either a bad connection or a damaged seal system.

Ian is correct - one must use as large a diameter as possible from a fusor to a DP. A gate valve of some type is essential if you plan on using deuterium (otherwise, usage will be extreme.) Your chamber will be, I assume, the four-way connector. That should work well but the DP will have to couple with that "chamber".

A plasma can easily be produced even at a torr using a neon-sign transformer (NST.) Again, these units are worthless for fusion but good for many other applications (I have two on hand and use them all the time: one powers a voltage multiplier (which I am posting too much on), another I use to test diodes and voltage dividers.) However, I got them very cheap - otherwise, no way since these are specialized devices unique to my needs.

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Re: Silicone tubing with hose barbs OK to pull low vacuum?

Post by Shireesh Apte » Fri Oct 27, 2017 6:19 pm

Thanks Ian, Dennis,

After liberally applying loctite to my joints, I got down to approximately 100 microns in about 20 seconds with my rotary vane pump. The set up is not pretty but I figured it would be good enough for a plasma. I believe I did obtain a plasma today (see pictures attached). The gauge reads approx. 100 microns with a glow emanating from the central grid and becoming more intense as the voltage (or what I believe to be the voltage regulator knob on my Chinese electroprecipitator) is increased.
I have realized that I will need to intensify work on the vacuum part of my apparatus if I want to progress to fusion. However, I did get permission to buy the deuterium cylinder from school administration based on my plasma demonstration, so that saves me some money.
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Shireesh Apte
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Re: Silicone tubing with hose barbs OK to pull low vacuum?

Post by Shireesh Apte » Fri Oct 27, 2017 6:26 pm

Many tanks to everyone on the board for the many useful suggestions. I will now start the long task of finding parts for - and assembling - a fusor.
Best,
Shireesh

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Dennis P Brown
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Re: Silicone tubing with hose barbs OK to pull low vacuum?

Post by Dennis P Brown » Fri Oct 27, 2017 6:42 pm

You certainly have created a true plasma. So congratulations on your success (Maybe PM Richard to include your name in the plasma club.)

Also, I thought you had a fusor chamber - that is, a four-way vacuum connector? If you have one of sufficient diameter, don't under value it. Those can make building a successful fusor easier.

I can't clearly read your vacuum gauge image but 100 microns is useful for a plasma, totally unacceptable for a DP based vacuum system that will be a fusor. When your system reaches 2 to 3 microns and exhibits a slow leak back rate, then you are ready for a diffusion pump and start of building a real fusor chamber that one can then hook up to a proper fusor power supply: remember, fusor supplies are always lethal so read the FAQ's on those systems and pay close attention to proper grounding. They are also significant x-ray hazards so a methodology to detect these is important.

As for deuterium gas, this is useless unless you have a power supply that is fusor capable. That is 20+ kV (with negative polarity) that can deliver at least two hundred watts of power or more (both more power and voltage is far better.) So, the next issue I believe, is what power supply do you currently have or are you planing on finding one? If you don't already have one finding those are difficult and not inexpensive. (Aside: a vacuum feed-thru that can handle both that level of power and voltage is important, too. I made my own but many just buy one - again, can be pricy.)

Finally, don't forget that one must prove they are doing fusion and that is a major issue that far exceeds the difficulties of building a fusor/vacuum system. Keep up the good efforts but you need to be aware that just adding deuterium to a plasma does not do fusion nor carries any importance in of itself - just another small step in building a possible working fusor.

As someone who often struggles myself with projects (my accelerator, for instance ... but you are seeing that in real time like most here; lol), I say these things to help guide you, as well as help you realize what to focus upon - not to discourage you; we all start somewhere and getting a plasma is the first real step in building a fusor.

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