Chamber Splattered With Vacuum Pump Oil

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Liam David
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Chamber Splattered With Vacuum Pump Oil

Post by Liam David »

I ran my demo fusor with a better vacuum a few times, and on the last run, after I opened the back-to-air valve, the chamber splattered with oil and filled with (smoke?). I had to clean every part of the chamber. Does anyone know what might have happened? Last thing I want to do is ruin my pump.
-Liam
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Chris Bradley
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Re: Chamber Splattered With Vacuum Pump Oil

Post by Chris Bradley »

Just a guess :/, your pump is between you chamber and the back-to-air valve?
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Re: Chamber Splattered With Vacuum Pump Oil

Post by John Futter »

You need an isolation valve in your backing line so as to isolate the pump. your air admittance valve should be on the chamber side of this isolation valve.
Some pumps have antiback flow valves which stop the oil being sucked out of the pump into the vacuum of the backing line, but experience has taught me not to rely on it as they do fail /leak and a massive clean up results.
you could add another air admittance valve close to the backing pump so you can open this as soon as you turn off the pump to stop the oil being sucked out of the pump.
You have learnt a good lesson and cleaning up the mess is a good reminder not to leave the outlet of your mech pump uunder vacuum when you switch off.
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Liam David
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Re: Chamber Splattered With Vacuum Pump Oil

Post by Liam David »

Yes, my pump is between my chamber and back to air valve. I'll add a valve in the vacuum line and then a back to air valve on the chamber side. Thanks!
-Liam
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Chris Bradley
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Re: Chamber Splattered With Vacuum Pump Oil

Post by Chris Bradley »

Yes, you should have the air valve on the chamber side, though if venting is to be uncommon then simply releasing a connection on the chamber and easing it off will be sufficient to vent it.

In fact, it is prefereable not to have a 'handy' vent valve to your chamber as it could be accidentally opened while the high vac pump is running and that will either be messy for a diff pump or it will kill a turbo.

You should form good habits when operating the chamber. For a 'standard' (i.e. typical amateur setup), whether a diff or turbo, you should turn off your high vacuum pump first and keep your backing pump running. Once the high vac pump has stopped/cooled, then if you are going to leave the setup under vacuum then close off the foreline valve and then shut the backing pump down.

When starting up again, always start the backing pump first and leave it for a moment before opening the foreline valve, otherwise if the foreline has come up to pressure then you'll get the same effect as you have just had, and you'll suck stuff into the chamber.

If you are going to vent to air, then again turn off the high vac pump and wait until it is stopped/cooled completely, then open the chamber whilst still pumping.

If you have a well-sealed system with a turbo, turn the turbo off and after a few moments while it is spooling down you can close the foreline valve and then turn the turbo and backing pump off. The turbo will continue to spool down and the vacuum pressure will be better preserved.

(You can even monitor turbo health if you do this - a ~60l/s turbo should take around 10 minutes to spool to a halt in a valved off vacuum. A Multi 100l/s turbo may take 20-30 mins, or more. You can measure the time it takes, and log it to make sure there are no anomalies with the pump.)

When turning off a backing pump, if it has a ballast valve then make sure it is closed. If you have been running with it open and you shut it off without closing it, it can also make a bit of a mess.

It is very sensible to write out check-lists for starting and stopping your particular system, as it is sure to have its own peculiarities. A check list should stop you making mistakes, and, frankly, I suspect we have all made such mistakes one time or another. Sometimes we are lucky and have gotten away with it, others not so. When/if you add gas handling, then again you will need to upgrade your checklists.

I have a vent bypass on its own valve where I can evacuate the gas lines to a reservoir through the chamber. I once made the mistake of venting the gas lines while the turbo was running. Fortunately this was a limited volume of air and the turbo survived, but of course it would have been dead if too much gas had come through. Check-lists are good.
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Richard Hull
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Re: Chamber Splattered With Vacuum Pump Oil

Post by Richard Hull »

There are complete operational details in the FAQs

Richard Hull
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Re: Chamber Splattered With Vacuum Pump Oil

Post by derekm »

I remember stern expressions on the faces the lab tech at Uni and the lecturer going over again and again what not to do with a diff pump experimental set up. Obviously born out of clearing up after ham fisted undergrads.
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