Poor performance of old diff pump.

Every fusor and fusion system seems to need a vacuum. This area is for detailed discussion of vacuum systems, materials, gauging, etc. related to fusor or fusion research.
Marcin Dziedzic
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Real name: Marcin Dziedzic

Re: Poor performance of old diff pump.

Post by Marcin Dziedzic » Fri Feb 08, 2019 5:05 pm

The pump has been dismantled, and turned out to be heavily damaged. The jest assembly is probably incomplete. The slits in jest assembly are bent in many places, and it's evident that the pump had been cleaned many times, marks from scratching with knife (!) are evident. :( The pump is not equipped with water-cooled coldcap and huge oil backstream destroyed two of my vacuum gauges (ITR90 and PTR91). I'll post a short story with photographs, for now I'm trying to replace it with new varian HS-20.

Jerry Biehler
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Re: Poor performance of old diff pump.

Post by Jerry Biehler » Mon Feb 11, 2019 5:12 am

The gauge heads ought to be able to be cleaned to get them working again. I would probably start by washing them out with mineral spirits to dissolve the oil and then acetone. I would be surprised if the filament on the ion gauge ever even turned on at the pressure you were getting.

Marcin Dziedzic
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Joined: Thu Dec 20, 2018 5:57 pm
Real name: Marcin Dziedzic

Re: Poor performance of old diff pump.

Post by Marcin Dziedzic » Sat May 11, 2019 12:49 pm

Ion gauge in Leybold ITR90 turns on at 2.4e-2 and turns off at 3.2e-2. In range between 2.4e-2 and 1e-3 output signal is combined from both Ion and Pirani gauges, hence old sensor name "combivac". Cleaning attempts turned out to be unsuccesful, the sensor was turning on ion gauge even at 5e-2 mbar, so the Pirani must have also been defective. The gauge was 6 years old, maybe it was just worn out, i replaced it with a new one.

My new pump has just arrived :) I'll see how high vacuum can I get.
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Bruce Meagher
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Re: Poor performance of old diff pump.

Post by Bruce Meagher » Sat May 11, 2019 6:31 pm

Wow that’s an impressive pump! Thanks for sharing and updating your post. I look forward to hearing how your system performs with your new pump. Many of the combo gauges have replaceable Pirani sensor. I’m not sure about your particular gauge (or if it’s really worth your time), but something to consider before you trash it.

Bruce

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