Foreline Pressure Measurement Issues

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Richard Hull
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Re: Foreline Pressure Measurement Issues

Post by Richard Hull »

Note if you bought your pump brand new from Harbor Freight or Northern Tool, these are less than top flight pumps (ChiCom) and 53 microns may be their bottom. Top Brand 5 CFM, direct drive, dual stage refrigeration pumps like Yellow jacket have little trouble hitting 10 microns.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Brianna Gopaul
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Re: Foreline Pressure Measurement Issues

Post by Brianna Gopaul »

Thanks John, I just sprayed IPA on each fitting from bottom to top and I saw no increase in pressure at each fitting, the pressure remained the same. This pump down I measured 42 microns compared to 53 microns last time, likely because the threadlocker cured for 24h. I'm a bit stuck on next steps right now. Clearly there is a leak somewhere given that I've measured 4 microns at intake. I was thinking of removing the KF adaptors but I doubt the o-ring and clamp is a leak source. I'll spend some time thinking about this and then test for vacuum leaks again to check.

Richard, the JB DV142N roughing pump is rated for 15 microns. I also measured 4 microns at the pump's intake so I don't believe this is the problem but thanks for the note.

Thanks,
Brianna
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Re: Foreline Pressure Measurement Issues

Post by John Futter »

I note you have not used the loctite 290 and have used another loctite product
the 290 is also called super wickin and is very fluid and designed to seal hydraulic fittings
once cured 290 does not appear to have any significant vapour pressure
Brianna Gopaul
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Re: Foreline Pressure Measurement Issues

Post by Brianna Gopaul »

Took a 2 week break for finals but I'm back:

Thanks John, I applied Loctite 290 to my fittings and let it cure for 2 weeks.
After 5 min, I got a foreline pressure of 17 microns.
I then opened the varian valve, the pressure skyrocketed and then went down to 28 microns (foreline + diffpump body)
From the FAQs, I know I should be aiming for a pressure of 12-15 microns for the foreline + diffpump body.

I'm thinking next steps are to check if the varian valve seals are faulty.
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Richard Hull
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Re: Foreline Pressure Measurement Issues

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Wow! I think you are sealed. That diff pump body is chamber sized! I would turn on the heater until the body warms just a little. (not too long though without oil) If the pressure goes up a lot, you have absorbed water that will leave once the oil is in the pump and reaches over 100 deg c.
Water in the pump in my imperfectly sealed system had to boil off after months of inactivity The system would hit 25 microns mechanical pump only with diff pump also evacuated. As the boilier got to work pressure would rise to 50 to 60 microns and then go down to 10 microns in the foreline.
Run the tests before going nuts only to find out you are chasing absorbed water in a chamber sized diff pump.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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