Roughing Pump Cooling

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Liam David
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Roughing Pump Cooling

Post by Liam David »

I have a roughing pump to get my chamber down to about 5 microns, and after about five minutes of operation, the pump casing gets almost too hot to touch. Does anyone have any recommendations for cooling it off? I've already tried using a fan, but that didn't work well. Don't want to fry a $150 pump.
-Liam
Alexandru_Calburean
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Re: Roughing Pump Cooling

Post by Alexandru_Calburean »

I have had luck before cooling very hot things by running copper tubing around the object and flowing very cool/cold water through the tubes. I would also recommend you keep the fan in this heat exchange setup as it will only help. Good luck with your efforts.

All the best,
~Alex Calburean
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Richard Hull
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Re: Roughing Pump Cooling

Post by Richard Hull »

Who made your pump. I assume it is a direct drive. Most pump motors run really hot while in use, especially if on for a long time. This is probably normal. normal.
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prestonbarrows
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Re: Roughing Pump Cooling

Post by prestonbarrows »

You can find manuals for most pumps online through google. This will tell you the normal operating temp. What power is the pump in watts? Do you have a vacuum gauge? You will need much less power when you get down towards the pump's ultimate pressure. If you are not getting as low as the pump is rated for (you can find that value in the manual too) this means either a problem with the pump like dirty oil or physical damage inside or a problem with the chamber causing a leak. All of these problems will cause your pump to work hard and get hotter.
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Chris Bradley
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Re: Roughing Pump Cooling

Post by Chris Bradley »

Liam David wrote: almost too hot to touch
Almost too hot to touch sounds like it is in the 45-50C range. Lots of electrical and electronics runs at this sort of temperature. If you try cooling down mechanical parts that are designed to run at a higher temperature, then you could damage them.

The other possibility is that you are pumping a big leak and are therefore getting the pump to work hard. If you are judging temperature on touch rather than measuring it (just like Newton did, so you are in good company!!!) then you are probably also guessing at 5 microns and have no gauge so you won't know if you have a big leak.

If it is a cheap 1 stage pump ($150?) then you will be no where remotely near 5 microns.
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Liam David
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Re: Roughing Pump Cooling

Post by Liam David »

No, is't a 2 stage pump. Its this one: http://www.ebay.ca/itm/2-Stage-3CFM-1-3 ... 0804858590? . I do have a large chamber leak because the plasma stays lit for only about 5 seconds after I switch off the pump, so that might be it. If it still runs hot after I fix the leak then I guess it's normal for the pump. Thanks for the info!
-Liam
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Re: Roughing Pump Cooling

Post by David Swan »

We have a Javac 2-stage pump in our physics dept. I was worried about it getting hot until I read the manual where it said the pump should run at about 60 deg. Running it too cold risks contaminating the oil with water vapur.

HTH
richnormand
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Re: Roughing Pump Cooling

Post by richnormand »

I don't know if your model is direct drive vs belt drive (slower)

My Leybold trivac D16A direct drive vane two stage pump with a 1Hp motor will get in the "too hot to touch long" with fingertips. It is its normal operating temperature but it takes about an hour to get there.
In the troubleshooting section they describe "pump running hot" as being 95C (about 200F). So mine is definitively not running too hot if I can put my finger about 1 sec before pain....

Check the oil to see its condition (clear and not foamy or whitish). Get a vacuum gauge and see if the pump reach "near" its spec base pressure (see Richard's FAQs on this subject).
If you are pumping lots of air (leak?) or should you have the ballast valve open the pump will run much hotter too.

If the pump is dragging or the oil is too viscous the motor will overheat by itself much faster that the vacuum pump.

Hope that helps.
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Liam David
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Re: Roughing Pump Cooling

Post by Liam David »

I found what might be causing my vacuum leak. The epoxy on the vacuum connection to the chamber didn't set right. I'll re-epoxy it using another brand and hope it holds.
Thanks for all the suggestions!
-Liam
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Re: Roughing Pump Cooling

Post by Alexandru_Calburean »

Liam,

I often use JB weld epoxy for anything related to vacuum connections, others have as well, and not only does it not out-gas but it seals well. I would recommend trying that.

All the best,
~Alex
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Re: Roughing Pump Cooling

Post by richnormand »

JB Weld on two joints with the turbo pump here.
It was meant to be temporary fix about one year ago but they are both still there. Base pressure around or better than 10^-7 torr so it cant be outgassing that much.

Make sure the mix is homogeneous and the surface well cleaned with some haze for grip. I used some fine emery paper on two interlocked stainless steel parts and pressed the JB for a few hours. Then removed the excess from the joint with an exacto knife while not totally set and hardened. A full day later I put the "welded" part on the lathe and made sure only the small ridge from the joint was exposed to vacuum to minimize epoxy surface exposure to the vacuum. Then used alconox soap to clean the parts, dried and a final wipe with acetone.

Mind the expansion coefficient if you are joining different metals exposed to large temperature variations or high temperatures (ie: not for parts that would be baked)

Over the years I find that the initial mix and surface prep are key for a solid joint with JB Weld. Nice stuff.
Good luck with the leak.
Last edited by richnormand on Fri Feb 07, 2014 3:20 pm, edited 1 time in total.
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Chris Bradley
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Re: Roughing Pump Cooling

Post by Chris Bradley »

Liam David wrote:I found what might be causing my vacuum leak.
You appear to have a piece of plexiglass simply held against a dry metal flange by g-clamps. I think you might want to start looking at that interface first.
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Re: Roughing Pump Cooling

Post by prestonbarrows »

Blank off the pump directly, with no chamber connected, if you want to test the pump itself. Then there is no question of leaks.
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Re: Roughing Pump Cooling

Post by derekm »

Liam David wrote:I have a roughing pump to get my chamber down to about 5 microns, and after about five minutes of operation, the pump casing gets almost too hot to touch. Does anyone have any recommendations for cooling it off? I've already tried using a fan, but that didn't work well. Don't want to fry a $150 pump.
-Liam
almost too hot to touch is around 50c to 60C. That seems normal. Some normal temps seem high... e.g. roller/ball bearing temperatures - they are recommend to be loaded up to run at 60C. Beware of strong electrical insulation smells though.
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Liam David
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Re: Roughing Pump Cooling

Post by Liam David »

Actually getting a 2.75" conflat tee vacuum chamber now, so that should stop most of the leaking and allow the pump to reach a lower pressure. The ISO tee setup is history.
-Liam
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