Scientific vs HVAC mechanical pump comparison

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.
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Nick Babusis
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Scientific vs HVAC mechanical pump comparison

Post by Nick Babusis »

I am comparing new HVAC pumps with used scientific pumps for backing my small diffusion pump (requires 0.6 CFM, 67 micron ultimate). Both types typically have the specs to back my diffusion pump, but 95% of used scientific pumps are being sold untested and I don't trust the ultimate pressure ratings on HVAC pumps. Typical examples of each are listed below. Can anyone advise on which is the better option for a fusor and future vacuum projects?

Typical HVAC Pump:
Model: Kozyvacu TA50
Link: https://tinyurl.com/yh483fck
Displacement: 5 CFM
Ultimate vacuum: 2.5 micron
Cost: $69

Typical Scientific Pump:
Model: Edwards E2M2
Link: https://tinyurl.com/yf8edb37
Displacement: 2 CFM
NEW ultimate vacuum: 0.8 micron (without ballast)
Cost $375

Neither model is actually tested, but eBay sellers typically accept returns and I have not been able to find a decent tested pump for <$500.
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Richard Hull
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Re: Scientific vs HVAC mechanical pump comparison

Post by Richard Hull »

Never, ever trust any specification on any brand new pump be it a brand new HVAC pump or the highest quality, most expensive new scientific rated pump.

They lie!

All, that is, 100% of used pumps for sale with no specific measured bottoming pressure at the head must be considered a roll of the dice with odds against you getting a good pump at any price.

A used pump, that when conditioned with new oil after a proper flushing, which pulls down to 15 microns or below, at the head, is a super win! 25 microns and just below is just a win.

All new 2 stage pumps should easily pump down to below 10 microns at the head.

All of the above is advice and tips to be found in the many vacuum FAQs written many years ago in the vacuum forum.

Why believe the people trying to sell you a brand new pump? They want your money and are driven to get it by glorious promises in advertising.

Note: the Edwards pump sitting in a drip pan to catch leaking oil is not a good look. Makes you wonder why they don't use it any more.

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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Sophie Yang
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Re: Scientific vs HVAC mechanical pump comparison

Post by Sophie Yang »

Believe me, because the actual vacuum system has gas load, you can't reach the rated limit vacuum at all. Therefore, it is impossible for Edwards E2M series mechanical pump to pull down to 0.8 micron.

I have used two new mechanical pumps Edwards E2M28 and Edwards RV12. In the actual working vacuum system, they only pull down to 1.1 microns. If you use a second-hand product, the limit vacuum you can pull down will only be worse. You need to replace pump oil to restore the factory performance of the mechanical pump. So you need to personally test the real performance of the old mechanical pump.
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Richard Hull
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Re: Scientific vs HVAC mechanical pump comparison

Post by Richard Hull »

Doing fusion by the amateur is not easy and many criteria must be met or exceeded throughout the system, touching on many scientific disciplines and technologies. Too many arrive here and feel they are up to the task. As I note in the FAQ related to this effort, it is not an easy road.

viewtopic.php?t=3247

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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