Chinese pump first run report.

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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Finn Hammer
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Chinese pump first run report.

Post by Finn Hammer » Wed May 17, 2017 2:38 pm

IMG_20170517_160046.jpg
Digivac meter showing 2 Microns on inlet of dual stage 10CFM pump from China
I received the Two-stage rotary vane pump the other day,
http://www.ebay.com/itm/2-stufig-Vakuum ... 1867425448
and was soon getting excited, since the label quoted two different values for acheivable vacuum.
either 0.004 Millibar, which corrresponds to 3 millitorr, but also 5 Pascal, which corresponds to 37 millitorr.
In the listing, it quoted 0.3 Pa which corresponds to 2.2 millitorr. What to expect?
Fortunately, the DigiVac LightBarVac meter arrived today, so at last I could start to get a feeling about the capability of the pump.

With everything in place, the pump drops down to, 5 micron, and within a minute or so, levels out at 1-2 microns, That is not so bad is it?

On the negative side, the pump does not have a ballast valve. I have no experience with vacuum whatsoever, and am unable to access whether this is going to be necessary pumping my 10" sphere, but time will tell.
I will probably dismiss this pump to vacuum jar duty, though, and get a proper lab pump, because this one is quite noisy, starts to get on my nerves already.....

Cheers, Finn Hammer

Johan Reinink
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Re: Chinese pump first run report.

Post by Johan Reinink » Thu May 18, 2017 3:55 pm

That's a good result for a 2-stage rotary vane pump. In my experience rotary vane vacuum pumps are always noisy but they're nice pumps. What do you consider a proper lab pump?
A gas ballast is needed if you pump a lot of condensible gasses, you probably won't need it anyway. Sometimes running a pump with the gas ballast open can clear out contaminations in the oil but your pump is performing just fine.

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Finn Hammer
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Re: Chinese pump first run report.

Post by Finn Hammer » Thu May 18, 2017 7:21 pm

Johan,

In my mind, a proper lab pump would have KF fittings instead of a Threaded connection, and it would have a ballast valve.
And it would be an Edwards, Varian, Leybold, Alcatel, Oerlicon, Pfeiffer, Agilent or some other of the really well built pumps.
A Welch would be nice but hard to get here in Europe. (I assume it is the one that goes lub lub lub :-) )

Cheers, Finn Hammer

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Dennis P Brown
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Re: Chinese pump first run report.

Post by Dennis P Brown » Fri May 19, 2017 12:27 pm

That is excellent performance for a two stage pump and if its pumping rate is good, you can't except much better than that.

A ballast is nice but one can just change the oil if that ever becomes a serious issue so don't worry about that.

Adding a KF adapter to a threaded pipe is easy since those types of adapters are readily available and not very expensive - just decide on the size that you will need for your foreline system. Most people prefer KF-25 (one inch diameter piping.)

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Richard Hull
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Re: Chinese pump first run report.

Post by Richard Hull » Fri May 19, 2017 9:47 pm

Dennis has given good advice. Old style lob...lub...lub... Welch and precision, belt drive pumps are much quieter and vastly more easy on my nerves. However what you have there is working great for you and will easily get the job done very well.

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Finn Hammer
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Re: Chinese pump first run report.

Post by Finn Hammer » Sat May 20, 2017 3:38 pm

Dennis and Richard,

Thank you for your replies and advice, it means a lot to me . Obviously, at this time, I am more or less walking in the dark, studying Vacuum and buying pats in a frenzy.
I have quite some past experience building pneumatics, and as such familiar with the difficulty of obtaining a tight joint using threaded connectors and teflon tape, it is a hit and miss affair. But with pneumatics, I could hear a leak, not so with Vacuum. So I intend to build the system one single joint at a time, testing for leaks as I advance.
O´Hanlons "A users guide to Vacuum Technology" arrived in my mailbox this morning, and reading it should bring me a step ahead, hopefully.
The next step will be to convert the pump to KF fittings and build a manifold, so that I can test the 2 pcs, used, 0.05 Millitorr, Baratrons I have coming, against each other, as well as against the Digivac, which is new and factory calibrated. With 50 microns of overlap, I should have a chance to measure down to 5 ^-2 MilliTorr and thus be set to measure relevant Vacuum levels.


Cheers, Finn Hammer

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Richard Hull
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Re: Chinese pump first run report.

Post by Richard Hull » Sat May 20, 2017 10:58 pm

You are on the right path with the right ideas. I have long held that a vacuum system should be tested one component added at a time and tested after addition. In this manner, issues such as leaks are immediately isolated and fixed one step at a time.

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

ian_krase
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Re: Chinese pump first run report.

Post by ian_krase » Sun May 21, 2017 1:44 am

Yeah.


I'll add that a very simple discharge tube, powered by a rectified NST, will provide you with a very fast-acting visual qualitative gauge for testing with Dust-Off.

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Dennis P Brown
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Re: Chinese pump first run report.

Post by Dennis P Brown » Mon May 22, 2017 9:46 am

While thread to thread compression fittings using teflon tape are possible/ok for torr and possibly the higher range micron systems, if you would like to obtain 10^-4 to 6 torr range, avoid using any connections that depend on teflon tape for sealing. Generally, teflon tape is only used in vacuum work for anti-seizing between fittings and not to seal said fittings. (most people evacuate their fusor's to 10^-5 torr or so.)

Since you are new and "Buying in a frenzy" I would suggest that you first learn a few things about vacuum systems to avoid many common mistakes. Do learn how to search (key words) ebay for stuff - amazing what might turn up and deals for systems that are very useful.

First, vacuum lines work best if they are as short and wide a diameter as possible relative to the inlet port of the vacuum pump/setup. Length matters a great deal - long lines need to be as large a diameter as is reasonable for the devices. For instance, while a 15 mm KF line can work if the line is short from the fore pump to the high vacuum pump, if the distance becomes a bit long, this can reduce performance and 25 mm KF will perform better.

The connection between your chamber and the high vacuum pump should be as large as possible - again, within constraints of the system. Most people directly mate a control valve/high vacuum device to the chamber.

KF connectors are fast to assemble/dis-assemble, tend to perform very well (and are not to difficult to re-polish when their surfaces are damaged) and are relatively cheap (can find deals all the time.)

For larger openings (where KF is not available) try to buy connector systems that are similar so one isn't trying to keep different types and sizes of sealing rings. Also, O-ring systems are very good for any fusor work.

Avoid using vacuum grease of any type - and when/if used, learn how to use it correctly. Correct is use as little as possible and then wipe that off with a clean, lint free cloth.

Never use water to clean any vacuum surfaces or o-rings (does not apply to freshly machined metal parts but cleaning them is a process that is involved.) Cleaning vacuum components (that could be contaminated by previous user) is tricky; most of us use as pure a solvent as we can obtain (generally ethyl alcohol - absolute is best); the issue/problem for over-ther-counter stuff is water content. Never use methanol - rather toxic.

Leak detection is a bit of an art and can be an issue. Learn how to handle leak detection for torr, micron, and high vacuum devices. Different methods and good vacuum gauges are a must.

Know that water vapor from the air will take a long time to get out of a system and can look like a leak; in other words, learn the difference between inner surface out gassing, virtual leaks (generally poor design), and real system leaks (too long to list but scratches on vacuum matting surfaces is a common one.)

Buy smart and avoid avoid buying used fittings - new saves more in time than any perceived savings in money; not necessarily true for larger diameter stuff.

Never buy a gate valve of any type that you can't return (which means you need to be able test it asap and so that means you first need the stuff to test it before buying such a unit) - vacuum valves can be real issues and tend to be expensive. Know what you want from your vacuum valve - manual/air drive/adjustable and total diameter issues as well as connector type.

If you are going for any high vacuum work (most fusors do), then knowing about diffusion pumps (air cooled/water cooled) and turbo's (various types and all require cables/control units) is important.

Vacuum gauges - know the units/ranges: torr, Pascal, micron, sub-microns. Know the range you need - atmospheric to sub-micron is extremely expensive and most of us use only a gauges for specific ranges of interest. For instance, every fusor MUST have some type of gauge that reads microns from 1 to 20/30 in microns (that is, need to resolve single micron digits - not tens of microns) and one high vac gauge (generally the 10^-3 torr range and below.).

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Re: Chinese pump first run report.

Post by David Kunkle » Wed May 24, 2017 3:57 am

My Trivac D4A in excellent condition can get to about 5 microns. You stated your Chinese pump gets down to 1-2 microns. I not sure any 2 stage pump can get that low- never mind a cheap Chinese pump. The accuracy of your TC gauge may be questionable. The 37 millitorr stated on the label seems more like it for a pump like that.
If your experiment needs statistics, you ought to have done a better experiment.

Ernest Rutherford

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