High Powered Rotary Vacuum 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.
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Blake Resnick
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High Powered Rotary Vacuum Pump

Post by Blake Resnick »

Hello,
I am currently in the market for a powerful vacuum pump. How does this one on ebay look? Does the price seem inline with the others of its class? Also, would I be able to just use some reinforced tubing to attach it to the vacuum chamber, or does this pump warrant something else?
Link: http://www.ebay.com/itm/Alcatel-Adixen- ... 35d865c89a
Thanks,
-Blake
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Bob Reite
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Re: High Powered Rotary Vacuum Pump

Post by Bob Reite »

You would still need a diffusion pump or turbo pump to get down to the pressures required. IMHO You might be able to find a better price for your backing pump.
The more reactive the materials, the more spectacular the failures.
The testing isn't over until the prototype is destroyed.
Blake Resnick
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Re: High Powered Rotary Vacuum Pump

Post by Blake Resnick »

This pump would be used for a demo fusor, not a neutron producing one. Therefore, it would pull a vacuum sufficiently deep.
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Scott Moroch
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Re: High Powered Rotary Vacuum Pump

Post by Scott Moroch »

To be honest you can probably find a pump for far cheaper that will suit your needs for a demo fusor. That is a lot of money to spend on only the pump. Keep in mind all of the other components that you will need to buy.

Best of luck,

Scott Moroch
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Jerry Biehler
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Re: High Powered Rotary Vacuum Pump

Post by Jerry Biehler »

Nice pump but I would not pay that much for one. You should be able to get it for half that.
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Richard Hull
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Re: High Powered Rotary Vacuum Pump

Post by Richard Hull »

The owner quotes the corporate specs. It runs fine, he says. Many pumps run just fine that are bad at pulling a rated vacuum.

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
Blake Resnick
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Re: High Powered Rotary Vacuum Pump

Post by Blake Resnick »

These pictures are of the plasma currently being formed at 28 inhg. As you can see the results are less than favorable... The chamber itself does not seem to be leaking, despite my scrutiny. So, I attribute the reactors poor vacuum performance to the cheap Harbor freight pump I am running. Is it likely this pump is running so far from its specified max vacuum? Could the chamber be leaking in a way that would be difficult to detect?
IMG_4795.JPG
IMG_4793.JPG
IMG_4791.JPG
Thanks,
-Blake
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Rich Feldman
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Re: High Powered Rotary Vacuum Pump

Post by Rich Feldman »

I bet you have a gross leak, not a bad pump.
[edit] And the pumping speed is limited by that thin hose of yours.
In the presence of a significant leak, the deluxe industrial pump
would perform no better than your Harbor Freight special. [\edit]

Make sure any gas ballast valve on the pump is closed.
Then when the pump is running, and chamber is pumped down,
there should not be any air flowing from the pump exhaust port.
(try plugging it with your finger).

You know the meaningful pressure must be measured up from zero, not down from atmosphere.
Lacking an absolute pressure gauge, you can use the plasma appearance to judge the gas pressure in chamber.

While the pump is running,
get a small brush and try applying a little vacuum pump oil to the outside of each joint:
- ends of cylinder
- HV feedthrough
- Vacuum gauge port
- Vacuum hose port and all hose connections

If you see any oil sucked in then you have found a leak.
Smaller leaks will be temporarily plugged by the oil, and the pressure will drop.
Plasma appearance and/or the sound of the pump may change.
It will react faster if you use a shorter or wider hose.
Good luck!

[edit] You could also install a valve between pump and chamber.
With chamber evacuated, close the valve.
How soon does the vacuum gauge move, or the plasma change?
All models are wrong; some models are useful. -- George Box
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Chris Bradley
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Re: High Powered Rotary Vacuum Pump

Post by Chris Bradley »

Why buy another pump when what you need is a micron capable pressure gauge to diagnose your existing set-up?

It's pretty mad asking about buying an expensive pump when you don't seem to even have a suitable pressure gauge.

It's also not very good asking after ebay items into the main forum, because it will be a dead link in a month. Put it in trading post, plz.
Blake Resnick
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Re: High Powered Rotary Vacuum Pump

Post by Blake Resnick »

All of your advice was hugely beneficial! I evacuated the chamber and found several large leaks. I also created a valve to stop the pump from leaking after its deactivation. Now, the chamber holds its vacuum for about 6 hours before returning to normal atmospheric pressure. Also, thank you for your advice regarding a more suitable gauge. How do these two look?

Links: http://www.amazon.com/Supco-VG64-Digita ... cuum+gauge
http://www.amazon.com/Yellow-Jacket-690 ... cuum+gauge

What do you think about the plasmas forming now? Also, do you have any idea what the bright white spot on the copper grid is?
IMG_1780.JPG
IMG_1766.JPG
IMG_1773.JPG
Thanks,
-Blake
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Richard Hull
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Re: High Powered Rotary Vacuum Pump

Post by Richard Hull »

Good enough to be in the Plasma club. I hope you will continue to imnprove your system.

Look at the name of the first guy ever admitted to the Plasma club back in 1998. Any relation?

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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Chris Bradley
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Re: High Powered Rotary Vacuum Pump

Post by Chris Bradley »

The gauges you point at are regular gauges for air conditioning engineers, however, they would actually perform a useful task, but what you really need is something that can measure sub-micron pressures so you know what's happening at that end of the vacuum scale. The ones you point at will simply read '0' when you get to the right point, but at least if they aren't reading '0' then you know it's too high!

I always recommend looking for active gauges. These can be Pirani (atm to fractions of microns), inverted magnetron (10s of microns down to 10^-9 mbar), or 'compact full range' that have both types in one device. The 'active' means you put power in and out comes an analogue voltage signal, no fuss. You have to keep you eyes peeled on ebay if you want the bargains, because these can go for Big Money [and seemingly higher and higher amounts these days - more amateur scientists than ever before, perhaps?], but you can still spot a bargain every so often.
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Dennis P Brown
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Re: High Powered Rotary Vacuum Pump

Post by Dennis P Brown »

With your system isolated, six hours from the bottom of your gauge reading (only 27 inch/Hg?) to atmosphere is rather poor performance for a sealed system. You still have leakage.

While even a fairly "tight" system will always rise due to outgassing (chamber walls/gaskets) but that should slow rapidly as it gets higher and should remain below atmosphere for a few days at worse (mine can stay below 50 torr for months but I have a high vac system that has been leakage tested in the low 10-6 torr. That is a very different requirement than what you need even for a neutron producing system.) Are all your threaded parts sealed properly - i.e. Teflon tape or a vacuum grade sealant? Did you use any type of grease on the gaskets (not a good idea in general. Gaskets at that pressure should never need any vacuum grease.) Your gauge is still far too high (should read 30, at least) or is it just a very poor quality gauge unable to read the real value? Possibly, the vacuum pump is poor and/or you still have a lot of leaking preventing your reaching 30 inch/Hg (Bottom of the gauge reading.)

From the picture your chamber looks very sound and if the gaskets are working properly they should easily bottom out that gauge.

Glade your system is doing far better but you have a ways to go if you decide to add (later) a high vac pump (turbo or diffusion.) If, however, that is not your goal, than your vacuum is fine for a demo.
Blake Resnick
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Re: High Powered Rotary Vacuum Pump

Post by Blake Resnick »

All of my threaded parts are indeed sealed, however the gaskets have quite a lot of high vacuum grease on them... Do you think that is contributing to its poor performance? The gauge itself seems to be fairly well made, however, tomorrow I have a much better gauge coming in. I am hopeful the new gauge will allow me to diagnose the system better. What kinds of pressure should I be reaching in order to accomplish star mode? (in microns if you could)
Thanks once again,
-Blake
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Rich Feldman
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Re: High Powered Rotary Vacuum Pump

Post by Rich Feldman »

Hi Blake.
Don't be too critical of your relative-to-atmosphere vacuum gauge, even though it appears to read low by somewhere between 5% and 10% when close to full deflection.
It's marked with the brand of Holley, a famous maker of high-performance carburetors.
[edit] That was in an older post of yours -- I see you switched gauges. [\edit]
I think an accuracy spec of +/- 10% could be considered normal for inexpensive Bourdon-tube gauges, and is good enough for tuning engines.

Here's a video that shows what goes into one of those gauges.
I imagine the manual adjustment step is often skipped to save cost.
http://www.youtube.com/watch?v=-xF7d0nuFTw

p.s. an absolute accuracy of +/- 10% would be considered excellent in a high-vacuum gauge.
All models are wrong; some models are useful. -- George Box
Dan Tibbets
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Re: High Powered Rotary Vacuum Pump

Post by Dan Tibbets »

I use similar tubing and it works fine. Provided my fittings are snug, I have no problems getting below ~ 50-70 Microns or even better if my diffusion pump is turned on. There have been reports that teflon tape is not ideal for sealing threads. Some type of lock tight or epoxy serves me well.

The first gauge is the one I have. You can buy them on E-Bay, or if you are close to an air conditioning repair/ supply store, they usually have some gauges in stock.

Dan Tibbets
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Werner Engel
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Re: High Powered Rotary Vacuum Pump

Post by Werner Engel »

A suitable vacuum gauge looks more like this: http://www.pfeiffer-vacuum.com/products ... doId=12202
Please go through the manuals there. Pfeiffer also provides a very good knowledge base for vacuum newbies http://www.pfeiffer-vacuum.com/know-how ... ner.action You don't have to do the math which is provided there, but it gives you an idea about how vacuum behaves: Imagine - the better the vacuum becomes, the more it behaves like honey, rather than a gas or a liquid. And at about 10-8 mbar its more like honey out of the freezer.

So it takes large diameters to "conduct" vacuum. A pipe with 40mm diameter is much better than one with only 6 mm.
The pipes should more look like this: http://www.vacom-shop.de/epages/VacomSh ... cts/302512

And using such gauges you can find your leaks much easier: Just take some small amount of a gas with higher molecular weight (dust cleaner, propan/butan from a gas lighter) and bring it close to the leak. Very small amounts of this gas will rapidly change the vacuum values on your gauge.
I use a pirani-cold-cathode combi gauge and found every little leak within a minute.
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Richard Hull
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Re: High Powered Rotary Vacuum Pump

Post by Richard Hull »

To answer the question above..........Decent star mode stars are generally found to be best below 20 microns. (10 microns is better)

A superior mechanical pump, in a well sealed system, can easily hit under 30 microns regularly and after a small run time and gas ballsting, end up at or below 20 microns. A good diff pump added to this will easily drop 2-3 more orders of magnitude to 10e-5 torr or better. These levels are not generally to be attained in a gasketed bell jar system with small tubing, greases and large gasket areas exposed to the vacuum.

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
Blake Resnick
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Re: High Powered Rotary Vacuum Pump

Post by Blake Resnick »

Interesting... I just attached my new gauge to the vacuum chamber, and with some more tinkering it reached 325 microns. I also removed the vacuum grease from the gaskets, which made the whole setup much easier to manage. The pump that I am currently running claims that it can reach 22 microns in a perfectly sealed system. The only areas where I believe the leaks are occurring is through the connections from the vacuum tubing to the fittings. However, I do not know of a way to remedy that. Currently, I have my fittings wrapped in teflon tape and covered in a bit of high vacuum grease. I am using a hose clamp to secure everything together. One thing is for certain though, I am defiantly feeling the limitations of my vacuum chamber...
Thanks,
-Blake
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Rich Feldman
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Re: High Powered Rotary Vacuum Pump

Post by Rich Feldman »

Blake,
You are learning fast.
What does your new vacuum gauge show when connected directly to the pump inlet,
using a minimum number of adapters and fittings, with no chamber or long hose?
You may find that the reading continues to drop for a while,
as the plumbing and the gauge itself outgas after long exposure to air.

To get favorable values for ultimate pressure, I have heard that pump makers use a McLeod gauge. That measures the volume reduction as a gas sample is brought up to atmospheric pressure. Vapors such as H2O will condense, so the vacuum reading does not include their partial pressure.

325 microns in your chamber is plenty low for common vacuum demonstrations, such as what happens to marshmallows. :-)
All models are wrong; some models are useful. -- George Box
Blake Resnick
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Re: High Powered Rotary Vacuum Pump

Post by Blake Resnick »

Thank you for the kind words. When the gauge is attached directly to the pump itself, its pressure equalizes at 40 microns. Quite the jump from the 325 of the chamber. I think that I will remove the valve in between the pump and reactor body to eliminate any more points of leakage. That should buy me a few more microns ;)
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Richard Hull
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Re: High Powered Rotary Vacuum Pump

Post by Richard Hull »

40 microns at the pump and 325 in the chamber tell us a lot about how leaky your system is, be it from outgassing (virtual leaks) to real leaks. There should normally be virtually zero differential between the pump head and the chamber in a well designed system.

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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Dennis P Brown
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Re: High Powered Rotary Vacuum Pump

Post by Dennis P Brown »

Vacuum grease on Teflon tape? Never - that defeats the purpose of the tape - makes it more likely to leak. Friction between the tape and metal surfaces is critical for deforming and forming a good seal. I use teflon tape in 10-3 torr systems with great success BUT it must be used properly AND only for specific situations (i.e. threaded systems designed for tape use.)

In general, vacuum grease isn't a good idea for any vacuum application but does have a few, rare uses. I'll skip that subject (the uses) but will say that for most people it is worse than useless and can cause major problems if used incorrectly.

If your pump can only reach 22 microns (mfd limit) than it isn't going to reach star-mode. As for your chamber only reaching 325 microns, that is rather poor. Consider re- tighten the chamber bolts while being VERY careful to get a uniform torque all around the gasket (that is, tighten each nut a little at a time in a sequential manner following a standard tightening pattern - look up this subject in auto repair on now to tighten head bolts. Tightening bolts on a chamber isn't as simple as many think and can lead to terrible leaks if done incorrectly!) And don't over tighten the bolts! That can lead to leaks, too. Your chamber looks very sound so the issue of the bolt tightening may be an issue.

I agree to remove that valve - it does not look vacuum grade at all. A larger pumping port and hose would, as some have pointed out, be a good idea.
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