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Thread: Vacuum loss with radiant heater.

Created on: 11/14/10 12:00 AM

Replies: 4

Abe





Joined: 11/14/10

Posts: 2

Vacuum loss with radiant heater.
11/14/10 5:07 AM

I'm very new and inexperienced to the whole industry and physics behind the processes, but very interested and willing to learn as much as possible.
I would greatly appreciate any answer to my problem with vacuum pressure failing when my radiant heater is switched on. I have just fully serviced both diffusion and backing pump, cleaning and replacing oils. The belljar has also been cleaned along with items contained.
The pressure is good until the heater is on. Is this normal considering the exposure to atmosphere and moisture when cleaned?. Is the problem likely to improve through use? Or is it possible the heat could be exposing a leak?.
The diffusion and backing pump appear to be working well.
The plant is an old Edwards. Guessing built in the 70's-80's. Mainly used for anti-reflection coatings and alumnising in a optical workshop.

My ignorance and lack of knowledge is probably amusing but I'm very lost and could use any help I can get.

Thanking you,
Abe
* Last updated by: admin on 9/30/2011 @ 10:10 PM *


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vacdepman





Joined: 06/05/10

Posts: 11

RE: Vacuum loss with radiant heater.
11/16/10 12:09 AM

The culprit is probably water vapor. The radiant heat caused the water vapor to desorb. To eliminate water vapor run a DC plasma discharge that desorbs the water vapor. Then pump down. i.e. pump - desorb - pump. DMM


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Abe





Joined: 11/14/10

Posts: 2

RE: Vacuum loss with radiant heater.
11/17/10 2:06 AM

Thank you for your response,
Is it more effective to run the plasma discharge when the vacuum preasure is higher?
Therefore allowing the vacuum to recover before another period of discharge?


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vacdepman





Joined: 06/05/10

Posts: 11

RE: Vacuum loss with radiant heater.
11/17/10 10:41 AM

If using a DC diode discharge the pressure will have to be above 10 mTorr or so to establish a plasma. The wall sheath then accelerates ions to the surfaces which then "scrubs" the surfaces of adsorbed molecules such as water. If you use air as the plasma gas the oxygen will react with hydrocarbons on the surface giving "reactive plasma cleaning" of the surface.


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vacdepman





Joined: 06/05/10

Posts: 11

RE: Vacuum loss with radiant heater.
11/17/10 3:33 PM

For more information on plasma cleaning search on glow bar plasma cleaning.


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