I am not sure if the picture is visible, so it is attached.. Dalibor
2013/1/26 Dalibor Farný <[email protected]> > Hello Jens, > > pretty sophisticaed way of leak detection ;-) > > what do You think by the "insufficient greasing on my needle valve"? The > rubber o-ring used to connect the valve to the system was not greased > properly? Or something else? > > "it is not airtight if the scale is adjusted to just zero" - does it > really let the outside air inside the system? I think that the valve stem > is not fully pressed to the valve seat when set to zero, when You screw it > further below zero, it gets full contact with valve seat this making thight > seal. Do You have the needle valve connected in right direction? To the > vacuum system should be connected the line what is on the left on that > picture: > > > > By the way, how long did You pump the system before closing and making the > test? I am also strugling with pressure rise, but it is caused by > outgassing of the materials inside the system - it goes from 5x10-3 torr to > 5x10-2 in 10 minutes and to 5x10-1 overnight, and all this pressure rise is > caused only by outgassing of rubber rings, air trapped in the metal surface > and so.. Let the pump run for one hour and then close it and do the test. > Or pump the system to 10-2 torr, close it, let it hold the pressure > overnight and then measure it. What pressures are You going to achieve for > pumping the nixies before filling by gas? > > What valve do You use for isolating the system from vacuum pump (is it the > ball valve we discussed recently)? > > Dalibor > > > > 2013/1/26 jb-electronics <[email protected]> > >> Hi folks, >> >> I am still working on Nixie tubes, but I have to take it a little slow at >> the moment because I switched my university and I am currently sort of >> living in two cities ;-) >> >> However, today I had some time so I took a look at my vacuum system. My >> problem was that even after I closed the valve to my pump at a pressure of >> 1.5E-2 mbar, the pressure would rise up to 20mbar in 20 minutes. So there >> was a leak. >> >> I then checked every part of my system (swagelok adapter, needle valve) >> by replacing them with a blind flange and recording the pressure after 10s, >> 20s, 30s, 40s, 50s, 60s, 120s, 300s, 600s, 1200s and plotted them. I >> realised that there was insufficient greasing on my needle valve, and the >> most interesting thing is that it is not airtight if the scale is adjusted >> to just zero. You have to (gently) adjust it below the scale zero point. >> Then I get a leakage rate of just 1.2 µbar/s which is very low. >> >> My system has a volume of at most (!) 65ml, so the leakage rate now is Q >> = 5.4E-6 mbar l/s which is pretty good I think. See my results here: >> >> http://www.jb-electronics.de/**tmp/leakage.png<http://www.jb-electronics.de/tmp/leakage.png> >> http://www.jb-electronics.de/**tmp/leakage_extensive.png<http://www.jb-electronics.de/tmp/leakage_extensive.png> >> >> Note that the Q value in these diagrams needs to be multiplied with 65ml. >> >> The next step will be to find a good connection to the pressure reducer >> for my gas bottle. Right now I am using a PVC hose (terrible), and I have >> huge leakage rates. >> >> But as always: One thing at a time ;-) >> >> Jens >> >> -- >> You received this message because you are subscribed to the Google Groups >> "neonixie-l" group. >> To post to this group, send an email to [email protected]. >> To unsubscribe from this group, send email to neonixie-l+unsubscribe@** >> googlegroups.com <neonixie-l%[email protected]>. >> For more options, visit >> https://groups.google.com/**groups/opt_out<https://groups.google.com/groups/opt_out> >> . >> >> >> > > > -- > Dalibor Farny > http://dalibor.farny.cz > > -- Dalibor Farny http://dalibor.farny.cz -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send an email to [email protected]. For more options, visit https://groups.google.com/groups/opt_out.
<<attachment: valve.jpg>>
