I suppose I could, theoretically, pump both the bell jar and the diffusion pump at the same time, but I think it would be a bad idea since the dp would rise to 1atm for a while.
We get down to about?
~9 to 7*10^-5 torr. Can't seem to go any lower. The coatings look good and seem to last a reasonable length of time (years).
On Dec 26, 2010, at 8:16 AM, "James Blackett" <
jamesrblackett@...> wrote:
?
Hi,
?
this seems very weird, I dont understand!! 200 mb
is very high. Can you pump the bell jar down without bypassing the diff pump?
what happens then? Because you can achieve a good final vacuum (how much?),
there cant be too much wrong with your system, I wonder if there is someting
wrong with the gauge(s), I've seen some pirani gauges do stupid things when they
have been contaminated,
?
sorry this is not much use, but just my
ramblings,
?
?
James
----- Original Message -----
Sent: Sunday, December 26, 2010 8:48
AM
Subject: [VacuumX] weird diffusion pump
behavior
?
Our old no-name,
government-surplus diffusion pump has a problem.?
After pumping the
diff pump for a while (minutes or hours, doesn't seem to make a difference)
and after loading the mirror to be coated into the bell jar, this is what
happens:
when I close the
connection between the mechanical pump and the diffusion pump, and begin
pumping down the bell jar directly, the pressure in the diffusion pump all of
a sudden rises dramatically, going up to ~200 millibars if I don't immediately
switch back to pumping down the diffusion pump directly again. It becomes
quite a dance, closing one valve then opening the other, then reversing again,
and again, and again.
Eventually it
always settles down and I get decent vacuum levels, but it's annoying for a
while.
?
Guy Brandenburg, Washington,
DC?
My blog, mostly
on Education in DC:
My
home page on astronomy, mathematics, education:or else
??=====================================
