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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"

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.

I don't think you were exceptionally lucky. I think explosions are
exceptional. Filthy messes and burnt oil all over the place I have
seen and smelled first hand. This was warning enough for me, especially
since I work with chemists who can rapidly emit sane physical
chemistry thinking and they too warn me of the potential worst case
scenario.

If one is concerned about this, one can even select oils according
to the physical properties that do not allow this.

Dominic

--- In VacuumX@..., Dominic-Luc Webb <dlwebb@c...> wrote:

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.

I don't think you were exceptionally lucky. I think explosions are
exceptional. Filthy messes and burnt oil all over the place I have
seen and smelled first hand. This was warning enough for me,

especially

since I work with chemists who can rapidly emit sane physical
chemistry thinking and they too warn me of the potential worst case
scenario.

If one is concerned about this, one can even select oils according
to the physical properties that do not allow this.

Dominic

diff pump explosion are something that is really exeptional these
day's due to the fact that in the early day's of the VD pumps the
pumping fluid where much more prone to oxidation less stable under
air at heat ( less flamability under oxidation ),today VD oils are
much safer from accidental back flash ( accident from atm
pressurisation of pump) especially the new high end types of oils
witch are stable even after an pressurisation mistake but in the more
expensive

please correct me if i am wrong

diff pump explosion are something that is really exeptional these
day's due to the fact that in the early day's of the VD pumps the
pumping fluid where much more prone to oxidation less stable under
air at heat ( less flamability under oxidation ),today VD oils are
much safer from accidental back flash ( accident from atm
pressurisation of pump) especially the new high end types of oils
witch are stable even after an pressurisation mistake but in the more
expensive

please correct me if i am wrong

Not at all; you hit it right on the mark! Some of us are essentially
amateurs building our own systems and this usually means looking
for lower price solutions. I would expect such people to read older
literature and deduce that there are cheaper solutions learnt long
ago, but the older literature will not tell you that the oils used
at the time were dangerous or that many years in the future there
will be safer oils (synthetics) being sold for considerably more money.

Dominic

On Friday, December 19, 2003, at 03:11 AM, Dominic-Luc Webb wrote:

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.

I don't think you were exceptionally lucky. I think explosions are
exceptional. Filthy messes and burnt oil all over the place I have
seen and smelled first hand. This was warning enough for me, especially
since I work with chemists who can rapidly emit sane physical
chemistry thinking and they too warn me of the potential worst case
scenario.

If one is concerned about this, one can even select oils according
to the physical properties that do not allow this.

My diff. pump uses a silicone fluid, specifically DC-704 (I think, I am
still waking up and my memory is less than stellar), so I assume (hah! there
he goes again assuming!) that I don't have to worry about this...

...........................................................
The problem with using bleeding edge technology is that the
blood that winds up on the floor is usually your own.

My diff. pump uses a silicone fluid, specifically DC-704 (I think, I am
still waking up and my memory is less than stellar), so I assume (hah!
there
he goes again assuming!) that I don't have to worry about this...

This pricy fluid should be quite safe from my reading.

Dominic

On Friday, December 19, 2003, at 09:26 AM, Dominic-Luc Webb wrote:

My diff. pump uses a silicone fluid, specifically DC-704 (I think, I am
still waking up and my memory is less than stellar), so I assume (hah!
there
he goes again assuming!) that I don't have to worry about this...

This pricy fluid should be quite safe from my reading.

Yes, its high cost probably makes it impractical for use (or Fomblin, etc)
by most amateurs (including me!) but I was very fortunate to be given about
500cc's of it by a good friend.