Greetings all,
I was recently working on my Ion vacuum gauge which entailed evacuating and
venting the chamber several times in a row. After about the 3rd evacuation, I
was getting a little too hasty and inadvertently left the Diff Pump foreline ->
rough pump valve open while at the same time opening the Chamber -> rough pump
valve, while the chamber was at room pressure!
I didn't catch the error until the chamber was down to ~2 torr, and I was
turning on the cold trap. While I may have been exceptionally lucky, no
explosions or fires! To my utter surprise the Diff Pump still pumped the
chamber down as usual, and I didn't notice any unusual smells, like burnt oil.
Since that experience I've coated several optics, so all is well.
On my to-do list is to add a feature to some how prevent opening the Chamber
rough out valve while the diff pump foreline valve is energized. One idea is
similar to how I quickly learned to turn off the high voltage plasma supply
before venting the chamber.
It only took one occasion to permanently educate me on checking the plasma
switch state. The education came about as the result of the chamber loosing
ground as the base-plate o-ring expands, which then leaves the chamber with a
~10KV potential. Since the chamber vent valve handle is attached to the
chamber, I was made rapidly aware of my mistake, and have since never repeated
it! :)
However, attaching a 110VAC wire to the chamber rough out valve handle may not
be a prudent idea, I am certain I would ALWAYS check the state of the diff pump
fore line valve before opening the chamber valve :)
BTW, the new 24" box coater made it to the shop last night, still have a lot of
work to do, but I hope to have initial leak testing done in the next few weeks!
;)
Take Care,
James Lerch
(My telescope construction,testing, and coating site)
"Anything that can happen, will happen" -Stephen Pollock from:
"Particle Physics for Non-Physicists: A Tour of the Microcosmos"