Hello all,
a friend of mine will supply me with a suitable adapter for 9mm glass
tubing. Really amazing! I actually found some at ebay for $20 or so as
well, the company Swagelok makes them (among others).
Thanks for drawing my attention to the ball valve. I checked, and as it
turns out it has been made for high vacuum applications, so I am
confused why it should be the source of the leak. Maybe there is no real
leak and it is just outgassing:
I need to get some vacuum grease and recheck the system after some
longer evacuation time, so thanks again for the hint, Dalibor and Ron!
Once I have re-greased the flanges I will leave the system running for
some time and then check the pressure.
Regarding the needle valve: I wanted a reliable valve that allows me to
adjust the neon partial pressure very accurately, because later on I
will also use this valve to let in argon (very low partial pressure) and
then fill up the rest with neon to create a penning mixture. For this
procedure I need an accurate valve. Granted, it might have been possible
to save a little money on this one, but I am not the craftsman to build
something like that by myself, so I took the shortcut of purchasing a
slightly overengineered valve. But then again, I only have to buy it once.
There are many ways to a well-working manifold. I chose the way of using
KF16 flanges for all parts, while others might find it more convenient
to build components on their own. But I really want to focus on
tube-making and not on building a ton of equipment which just takes too
much time for me.
But then again, it is up to everybody's personal habits and abilities.
Jens
Hello!
You most likely have a serious leak in the ball valve. You might get
temporary seal in it by disassembling it and packing the seal areas
solid with vacuum grease. This would be temporary and subject to begin
leaking again at any time but could give you a few days of leak free
operation without changing out the valve to a better one. You would do
better to get a hardware store water valve with a standard packing
that you could remove and replace with a teflon plug packing. I have
done this and made valves that are tight to 10 -6 torr! Be sure to get
a "plug" valve and not a gate valve. (a plug valve rams a rubber plug
onto a seal surface. A gate valve slides a metal gate into a groove.)
You should not have any problems at all with the rubber hose in those
short sections so long as you use grease on the connections.
Permeability of the rubber is minimal at room temperature and would
take hours to affect the vacuum at the pressures you are using. How
long will the pressure stay constant when you turn off the power and
close the ball valve? It should remain below 100 microns for several
hours if you don't have a leak. Important: Note that to outgas the
system to do this test it will take about 4 hours of continuous
pumping regardless of leaks! (surprise?!) Yes, it takes that long if
you cannot heat the system a bit with a torch or heat lamp! Most new
users in vacuum are very surprised at how long it actually takes to
outgas a system that has been at atmospheric for any length of time!
You may not have a leak, just normal outgassing!
Just out of curiosity, why do you need such a close control of the
neon into the tube? For nixies it surely isn't necessary. What are you
going to make?????
glasslinger
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