Foreline valve and trap - what is neccesary?

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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Dennis P Brown
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Re: Foreline valve and trap - what is neccesary?

Post by Dennis P Brown » Sat May 23, 2020 9:33 pm

Until you get a proper valve, the simple solution is to leave the mechanical pump running - turn off the turbo; then allow it to spin down (assuming you have no mid-point vent built into the turbo body.) After it stops, turn off the mechanical pump and let air into the system. No oil vapor back flow issues (just water vapor but for most fusor's, that issue isn't too big a problem if you first run the system down to the 10^-5 torr range before opertaion.)

ChristofferBraestrup
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Re: Foreline valve and trap - what is neccesary?

Post by ChristofferBraestrup » Sat May 23, 2020 11:38 pm

Okay so this is exactly what I wanted to do in the first place. I thought the higher vacuum once the turbo slows would 'suck' oil back from the roughing pump even though it kept running.

And I do have a mid-point turbo vent valve, both solenoid and manual.

John Futter
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Re: Foreline valve and trap - what is neccesary?

Post by John Futter » Sun May 24, 2020 7:01 pm

you should also have an activated alumina trap in the roughing line to stop oil vapor from the backing pump backstreaming into the turbo wwhen at high vac with no leaks

ChristofferBraestrup
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Re: Foreline valve and trap - what is neccesary?

Post by ChristofferBraestrup » Sun May 24, 2020 7:59 pm

I should, yeah, but that is less critical as far as I know. The magnitude of oil is a trillion times lower than sucking half a litre oil back into the pump!

I wouldn't be terrified about pumping down the system without a foreline trap.

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