Guy,
What do you mean: "when I close connection between the mechanical
pump and the diffusion pump"? If you close backing valve and open
gate valve, system won't work.? Only cryo and other sorption pumps
work with closed backing valve. Dif and turbo pumps must be backed
always.
Do you have gauge on the dif pump input flange under the gate valve
and on its output? What are the pressures?
Sometimes valves may leak in some position, for instance, there is
no leak when it closed and a great leak when it opened. So
everything looks fine when a gate valve is closed, and a big leak
appears when you open it for high vacuum pumping.
Best regards,
Vladimir
On 12/26/2010 12:48 AM, Guy Brandenburg wrote:
toggle quoted message
Show quoted text
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 ??
=====================================
