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Registered Member #1134
Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351
Very cool!
You will likely need a larger diameter, and shorter vacuum line to pump down the Diffusion pump.
A few posts back I had said that I was using copper brake line on the low side, and that the fittings on the pump manifold (1/4" SAE) were much too small, and were doing a marvelous job of choking what could be a good pump!
For this reason I was using two of the available ports, however I wasn't really happy with using such narrow diameter tubes, so last night I disassembled the pump manifold, and modified it a little.
There are three fittings on the javac inlet, a 1/4" SAE, a 3/8" SAE, and 1/2" acme. The acme is on top of the inlet, providing the path of least resistance for the pumped gases, and is also has the largest internal diameter, so I modified this port.
The internal diameter of the 1/2" acme is just over 6mm, and it turns out after removing it from the pump body, that the internal diameter of the inlet manifold is 10mm, so I bored out the center of the acme to 10mm for maximum possible flow rate.
I soldered on a 1/2" speedivac coupling I had in my box of junk. A more modern flange might have been better, but this is quite satisfactory for now.
Above: The complete coupling on the manifold.
The results:
To the other half of the coupling I soldered a 6" length of standard 15mm copper plumbing pipe, that just happened to fit quite snugly in the 1/2" speedivac fitting.
To this I attached one of my glass discharge tubes, shown further up the post, connected up the EHT supply, and fired up the pump. The flow rate and base pressure now is simply amazing! It will pump down to a "soft x-ray" vacuum (i.e. the luminous discharge in the tube will cease, and the tube will produce x-rays) in about 5 seconds, all by itself!
Before, it would take around 15minutes to reach base pressure, and this was quite a way away from the vacuum it pulls now.
There is no doubt now, that the pump will be capable of forepumping quite large diffusion pumps, and once I hook it up to my small diffusion pump, I expect the ultimate vacuum of the system to be much much deeper.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Coo that's good, Les!
I very recently bought a lot of seven Mini-Instruments Mini-Monitors, together with ten Alrad Gammatell II, and three branded only "Harwell Dose Meter" in an ex-Harwell auction, £23 the lot.
The Gammatell IIs use tin foil compensated ZP1313 mini GM tubes and have a cute little 500V supply the size of a double sugar cube.
I'll re-calibrate these instruments with a function generator when I've finished refurbishing them.
The Alrad Gammatells run from a standard PP3 9V battery and have a red LED display in total uSv (push button to view), and a dose-rate alarm with five levels (uSv/hr) which can be selected by moving an agreeably simple internal jumper. The three yellow "Harwell Dose Meter" also have a programmable alarm but use a 3V battery and have an LCD display
I'll send you a Gammatell II when I've rigourously tested them over one month's continuous operation.
Registered Member #1134
Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351
Proud Mary wrote ...
I'll send you a Gammatell II when I've rigourously tested them over one month's continuous operation.
Thanks! Thats jolly decent of you!
My 1/2" "vacuum hose", turned up today. I was looking for wire reinforced PVC pipe for the low side. I scoured the 'net for the boomin' stuff, and it was only when I was looking on evilBay for a reaction vessel, that I found some being sold by the biodiesel crowd as suction hose.
In case anyone was wondering, wire reinforced PVC is ideal for medium vacuum use, i.e. connecting your forepumps to your diff pumps, for the high vacuum side, you really do need metal.
I will fire up a pic of the new setup once my valves turn up, and are fitted
Registered Member #1134
Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351
Here is the diffusion pump with 1/2" reinforced hose, attached to the modified manifold.
Some of the more observant among you, might also notice I removed the fitting on the Diffusion pump, that necked the pipe down to 8mm. Now the high vacuum side is 15mm diameter, with only one solder joint.
Every little helps with these things! I am happy with it now as it stands.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
My Goodness, Fabio! What a splendid piece of work! And your great metal beehive makes my diffusion pumps look tiny. But size isn't everything, you know!
Registered Member #122
Joined: Fri Feb 10 2006, 12:55PM
Location: Milano Italy
Posts: 148
i fixed and connected everything on the cooling system last week but, unfortunately, the diaphragm pump i used for liquid circulation is too violent, it acts as hidraulic ram and force the internal baffle of the diffusion pump to vibrate vigorously.
to avoid any risk of damages, i must add something to smooth the hidraulic flux coming from the pump, a water reservoir with an huge air bubble inside should work fine.
This is my solution of the problem, i made a transparent reservoir with a water fountain inside for both aestethical and pratical purposes (i can clearly see if i have a liquid flux or i have occlusion problems)
Registered Member #1667
Joined: Sat Aug 30 2008, 09:57PM
Location:
Posts: 373
forgive me for disturbing the dead (threads), I just found an interesting publication on the electron beam induced radiolysis of organic pollutants:
"Boron Nitride Electron Permeable Windows Used In Electron Beam Water Treatment"
Basically, you'd break up organic compounds by direct radiolysis and by introducing free radicals. The radiation dose in the kGy range however seems to be intimidating. Maybe there is something to be learnt in the context of food irradiation, too.
Aromatic compounds can be qualitatively analyzed with aluminium chloride. I'm not asking plazmatron to do the experiment, just wanted to hint to its existence
plazmatron wrote ...
... wrote ...
That is amazing :-o
A little ebay searching turned up some 9um (.3mil!) thick Ti foil, I wonder if it would hold to 15psi or not
What are you planning to do with this new toy?
Thanks for the link, I was just having a dig myself! 9µ should be easily able to handle the the pressure, the window is only 5mm diameter after all. I hear that ordinary kitchen foil is around 16µ so 9µ in Ti should be ideal.
Well the diff pump will be used for allsorts of vacuum work, the Lenard tube was something of a diversion But, since it is a very interesting diversion, it will have to be scaled up a little. I figure a 250kV tube would satisfy my curiosity!
Les
ps. At higher energies in conjunction with oxide surfaces, even more intriguing reactions happen, leading to the production of molecular hydrogen: "Zirconia is thus found to produce high amounts of H2 (Figure 1) [60], which is due to the scavenging of excitons by adsorbed water molecules, as also shown by thermostimulated luminescence experiments."
Registered Member #1134
Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351
hboy007 wrote ...
forgive me for disturbing the dead (threads), I just found an interesting publication on the electron beam induced radiolysis of organic pollutants:
"Boron Nitride Electron Permeable Windows Used In Electron Beam Water Treatment"
Basically, you'd break up organic compounds by direct radiolysis and by introducing free radicals. The radiation dose in the kGy range however seems to be intimidating. Maybe there is something to be learnt in the context of food irradiation, too.
Aromatic compounds can be qualitatively analyzed with aluminium chloride. I'm not asking plazmatron to do the experiment, just wanted to hint to its existence
Not dead, just slumbering!
Stella mentioned Boron Nitride windows some time back, as possible x-ray windows, since they are very transparent to low energy x-rays, which is one of our interests.
It is expensive stuff though! It is possible for x-rays to use polyethylene, and any number of other light polymers, on a continuously pumped system. Although the electrons and x-rays will destroy the window, they will last long enough to perform a variety of experiments, and are inexpensive enough to be considered consumables.
For electrons, obviously a polymer would be destroyed almost instantly.
Incidentally, the Titanium window I made was much too thin, and ignited from the electron impact in my Lenard tube!
I did however, manage to use ordinary aluminium foil effectively, once I redesigned the tube:
This tube used a carbon fibre cold cathode, and worked extremely well. The camera did not pick up the blue glow as well as the dark adapted eye can, and it extended some 3 cm out from the window at 60kV or so.
These are particularly dangerous devices, and whilst I am happy that I built it, it isn't something I would want to work around to investigate radiochemistry. Low energy x-rays are much, much safer!
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Diffusion pump project
