Two questions about diffusion pumps.
Does one normally run the pump heater "wide open"? What I mean is there any reason to place a variac in the heater circuit to reduce the amount of heating?
And for question #2: Does the pump "use" oil? I'm asking this because when I disassembeled my pump to change the oil the level seemed lower than I had originally set it.
Diffusion pump questions
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Jon Rosenstiel
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- Joined: Thu Jun 28, 2001 1:30 am
- Real name: Jon Rosenstiel
- Location: Southern California
Re: Diffusion pump questions
The pump itself does not "use" oil, but the oil can escape from the pump.
To the best of my knowledge, the primary way this occurs is backstreaming - diffusion pump oil escaping into the chamber through the inlet port. But I can't image that the loss due to backstreaming from a single, or even a few, pumping sessions would make a very noticable difference in oil level.
Just how much different does the oil level appear to be?
-Ryan Edgar
To the best of my knowledge, the primary way this occurs is backstreaming - diffusion pump oil escaping into the chamber through the inlet port. But I can't image that the loss due to backstreaming from a single, or even a few, pumping sessions would make a very noticable difference in oil level.
Just how much different does the oil level appear to be?
-Ryan Edgar
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guest
Re: Diffusion pump questions
Short answers: Yes, the heater (if it is sized correctly) must run at full power. Running at less than full power, will cause the diff pump oil to boil more slowly or not at all. Since the oil vapor does the pumping, the pump speed will be adversely affected.
Secondly, the diffusion pump oil is not normally "consumed" in the usual sense. However, depending on the operating pressure of the pump, some oil may, over a long time, be oxidized away. This comes about usually from accidental high pressure excursions caused by leaks or a somewhat over enthusiastic operator routinely rushing the pumpdown transition from rough to high vacuum.
Secondly, the diffusion pump oil is not normally "consumed" in the usual sense. However, depending on the operating pressure of the pump, some oil may, over a long time, be oxidized away. This comes about usually from accidental high pressure excursions caused by leaks or a somewhat over enthusiastic operator routinely rushing the pumpdown transition from rough to high vacuum.
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guest
Re: Diffusion pump questions
I had originally set the oil level at 7/8", (By the way, the pump is a 2" water cooled Veeco). When I took it apart it was around 1/2". Now that I think about I originally measured the oil level with the baffle tower in place, but when it was at 1/2" the tower was removed. Duh!
Looks like I answered my own question!
The oil and the pump internals were still quite clean, though there was a slight film of oil inside the vacuum manifold just above the pump inlet. Normal operation I suppose.
Looks like I answered my own question!
The oil and the pump internals were still quite clean, though there was a slight film of oil inside the vacuum manifold just above the pump inlet. Normal operation I suppose.