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.
John Futter
Posts: 1848
Joined: Wed Apr 21, 2004 10:29 pm
Real name: John Futter
Contact:

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

Post by John Futter »

Waterjet cutting shop will cut glass of any normal thickness up to at least an inch thick
User avatar
Dennis P Brown
Posts: 3159
Joined: Sun May 20, 2012 10:46 am
Real name: Dennis Brown

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

Post by Dennis P Brown »

I cut holes in glass plates up to 3/4 inch thick by up to one inch in diameter easily; I bought an inexpensive set of diamond abrasive hole saw bits from china (these work very well.) I put plumbers putty around the area to be drilled. Then I fill in about 1/2 inch of water and include a drop of dish washing soap (add water as needed.) Using a hand drill (but a drill press makes straighter/cleaner cuts) - I drill through the glass slowly: raise and re-engage the glass hole with the bit often to let the bit/glass drilled area cool. I have done many cuts and never had an issue except when using a hand drill: using such a drill allows the bit, at first,to try and "walk" away across the surface. A steady hand and trying to get the bit edge to bite into the glass (don't push too hard but rather, very, very slightly, favor a side) to anchor the cut is all you can do; a drill press avoids this issue. If you have a drill press, always use the highest speed setting.

Well, I guess Richard can add your name to the plasma club. You should PM him with the request and reference your plasma results.

Looks like your pump has issues or else the vacuum gauge has issues; or both. My guess is the pump since it does not appear to be a two stage unit. Do show a picture of your vacuum gauge system (the micron unit.) You should easily get below 1 torr with most vacuum pumps. Micron gauges, cheap ones or TC ones do have issues with pressures in the high range close to 1000 microns. So you could be near 800 microns and the gauge would still not record this. Maybe a better gauge (there are good gauges that read in the low torr range to sub-torr accurately but cost can be an issue.) That is why most here get a high end two stage pump and use inexpensive TC gauges to read microns since our pumps easily get down to a few microns or less. It all depends on ones available funds, knowledge and skill set/experience. One only gets experience by trying like you are now doing.

A few minor notes: we do not use inches of Hg here; torr is often used here (or one can use SI units: Pascal or Bar.) There is absolutely no such things as "-749.3 mm Hg"; yes, refrigerator people use negative inches of Hg to spec the difference from atmospheric pressure but do not use those units in high vac work nor use them here; you need to learn what units are and mean. Atmospheric pressure is about 760 torr; 1 torr equals 1000 microns. At and below 1.0 micron one uses scientific notation for torr units; i.e. 1 micron equals 1*10^-3 torr.

One does not refer to a vacuum chamber as a fusor unless one has a system that can handle real attempts at fusion (i.e. will need deuterium, and at least the ability to create the required power/voltage in an acceptable vacuum.) Nor is it a reactor unless one is doing real fusion - a very high bar to achieve because one must prove that statement (this issue is not relevant here.) However, do keep at it. You are making progress and that's how one can achieve a goal of getting in the neutron club.

Don't get discouraged: I have generated and detected neutrons and I am still struggling to learn elementary aspects about high voltage multipliers (lol.)

To get started in any real high vacuum work the first two absolute requirements are a good two stage pump that gets down to a few microns (i.e. below 2 or 3 mircons; generally mfg will claim sub-micron) and a gauge that accurately measures microns (100 and below.)
Shireesh Apte
Posts: 26
Joined: Sun Sep 10, 2017 10:16 am
Real name: Shireesh Apte

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

Post by Shireesh Apte »

Thanks Dennis, John,

I am using a 2 stage, 4 CFM rotary vane vacuum pump. The pump indicates that it can go down to 3 X 10^-1 Pa, or 2.25 X 10^-3 mmHg (2.25 microns). I realize that this magnitude may not be reached, but it seems to me that it should be able to pump down to <100 microns, where one could get a plasma. I have attached the gauge to the vacuum pump inlet. If I indeed have generated a plasma, then it would seem that the pressure is much lower than what the roughing gauge displays (calculated to be 18800 microns or 18 mmHg). The issue I am having is that when I attach the micron gauge to the pump, it always reads OL(overload) ( I have seen it read 5000 microns before). Therefore, I am going to attach the micron gauge to my set up again and tighten the connections. I should be able to do this today.
An accurate pressure reading will help me when I eventually run a diffusion pump and start to work toward fusion.
I have pictures of my roughing pressure gauge, vacuum pump and micron gauge below.
20171017_094630.jpg
20171017_094711.jpg
20171017_094648.jpg
Shireesh Apte
Posts: 26
Joined: Sun Sep 10, 2017 10:16 am
Real name: Shireesh Apte

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

Post by Shireesh Apte »

Here are pictures showing the micron vacuum gauge connected to the pump. I have been pumping for about 2 minutes now with the gauge still reading overload. I will try for about 15 minutes later.
Best,
Shireesh Apte
20171017_102535.jpg
20171017_102519.jpg
User avatar
Dennis P Brown
Posts: 3159
Joined: Sun May 20, 2012 10:46 am
Real name: Dennis Brown

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

Post by Dennis P Brown »

Well, a number of issues: the connections you are using are not suitable for vacuum work - those compression fittings are extremely difficult to get a good quality seal and it is best if you abandon them. Your "micron" vac gauge is not using a standard connector either and those types that it has may cause issues with high vac.

Unless you can get below 50 microns, a diffusion pump should not be used.

The plastic line you are using isn't suitable for vacuum work - the plasticizer will out gas badly.

You need to look at kf flange systems (they use o-rings) and work very well for most fusors. These can be had rather inexpensively on ebay - especially used systems. Mating to your gauge isn't going to work so maybe best to get a conventional TC gauge that reads in the microns (but are fairly useless above 200 microns.)

Try pumping just on your vacuum gauge - having a plastic line still connected isn't the proper method - use just the gauge head. See what the pump can do. If it still can't read then either those compression fittings are leaking terribly or else the gauge is no good or the pump is no good or some/all of these.
User avatar
Richard Hull
Moderator
Posts: 14991
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

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

Post by Richard Hull »

Dennis is correct. How are you to diagnose your pump and find how low it will go when also pumping your system??? Your system might be the source of leaks. Attach the gauge and only the gauge to the pump inlet.... no hose allowed.

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Shireesh Apte
Posts: 26
Joined: Sun Sep 10, 2017 10:16 am
Real name: Shireesh Apte

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

Post by Shireesh Apte »

Thanks Dennis and Richard,

I actually did do this some weeks ago with ambiguous results - I don't remember what the exact reading was on the micron gauge ( my apologies, I have too many students clamoring for grade betterment now that it is almost the end of the quarter). However, I am going to do this again by removing the barb fitting and mating the pump with a proper screw on end-cap. I agree, I want to see the micron gauge read between 1 and 10 microns or slightly above so that I can then install the diffusion pump between the fusor and the rotary vane pump and move on with the fusion part of the project.

Best,
Shireesh Apte
Shireesh Apte
Posts: 26
Joined: Sun Sep 10, 2017 10:16 am
Real name: Shireesh Apte

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

Post by Shireesh Apte »

As you can see, after attaching the micron gauge (still with a compression joint) to the pump inlet, I get a reading of approximately 1.4 mmHg (1400 microns) after pumping for 20 minutes with a 2 stage 4 CFM rotary vane pump. The pump comes with a female flared threaded 3/8th inch to which I have attached the compression fitting of the micron gauge. The next step will be to apply loctite to the joints and check pressure again.
I am in the process of ordering NPT to KF-25 adapters but I don't know if they will work with a flared fitting. I am shooting for a vacuum of at least <100 microns using the rotary pump alone.
Best,
Shireesh Apte
20171023_075422.jpg
Nnnnnnn
Posts: 58
Joined: Tue Jun 13, 2017 6:25 pm
Real name: Niels Geerits

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

Post by Nnnnnnn »

Shireesh, my pump is 1/4" flare. If you want to go to any other connection type you need a special adapter. I got a flare to 3/8" BSP adapter it comes with a piece of copper that you have to put in between the flare and the adapter to get a good seal. I had to contact the pump manufacturer to get the adapter. In the thread I started on my TC gauge you can see I got about 4 out of 10 mV out of the gauge. This is because I did not use a sealing ring on the BSP connectors. This is more than good enough to start my turbo though.

Which secondary pump do you plan on using? Afaik a diffusion pump will need a lower fore pressure than a turbo (mine is rated at 14 mbar)
Dan Knapp
Posts: 402
Joined: Wed Aug 06, 2008 8:34 am
Real name: Dan Knapp

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

Post by Dan Knapp »

From your pictures, it looks like your tubing is Tygon rather than silicone. Tygon tubing is commonly used on vacuum systems for forevacuum lines, but in larger diameter than yours. The tubing you are using is very small for a forevacuum line; the low conductance of the narrow tubing will significantly reduce your pumping speed. Tygon forevacuum lines must be heavy wall or have a metal spiral spring inside to keep the wide bore tubing from collapsing under vacuum. The plasticiser in Tygon is usually dioctyl phthalate, which has a vapor pressure in the 10e-7 Torr range; thus it is not a problem in forevacuum lines. Hose barb fittings are commonly used with Tygon forevacuum lines, but with hose clamps. Properly assembled compression fittings are adequate for forevacuum lines, but again yours are very narrow bore for this application.
User avatar
Dennis P Brown
Posts: 3159
Joined: Sun May 20, 2012 10:46 am
Real name: Dennis Brown

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

Post by Dennis P Brown »

Then either the pump has issues, the gauge does or more likely, your connector system is leaking very badly.
User avatar
Richard Hull
Moderator
Posts: 14991
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

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

Post by Richard Hull »

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!

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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Shireesh Apte
Posts: 26
Joined: Sun Sep 10, 2017 10:16 am
Real name: Shireesh Apte

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

Post by Shireesh Apte »

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
ian_krase
Posts: 636
Joined: Mon Nov 28, 2016 2:48 am
Real name: Ian Krase

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

Post by ian_krase »

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.
User avatar
Dennis P Brown
Posts: 3159
Joined: Sun May 20, 2012 10:46 am
Real name: Dennis Brown

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

Post by Dennis P Brown »

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.
Shireesh Apte
Posts: 26
Joined: Sun Sep 10, 2017 10:16 am
Real name: Shireesh Apte

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

Post by Shireesh Apte »

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.
20171027_101547.jpg
20171027_101728.jpg
20171027_101533.jpg
20171027_101618.jpg
Shireesh Apte
Posts: 26
Joined: Sun Sep 10, 2017 10:16 am
Real name: Shireesh Apte

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

Post by Shireesh Apte »

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
User avatar
Dennis P Brown
Posts: 3159
Joined: Sun May 20, 2012 10:46 am
Real name: Dennis Brown

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

Post by Dennis P Brown »

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.
Post Reply

Return to “Vacuum Technology (& FAQs)”