Regrind the seal face of a flange of a turbo pump for better vacuum

[Pascal Mueller]

Hi,

so I am still searching for nice pumps and I came across this item here. The price was a bit high I think but reading the description raised some questions I'd like to discuss.

So apparently the pump (Turbovac SL80) made it to 10e-4 mbar. It takes 3mins to get to full speed. He doesn't know if it gets any better because he doesn't have the equipment. Anyway, he's saying in the description of the auction that the seal surface of the flange on the turbo pump has some scratches. So to get a better end vacuum, one might have to regrind this surface.

Now I am wondering: How would one regrind such a surface? What would you use? (Note, the SL80 is apparently capable of an vacuum of 10e-10mbar) Any experience how such scratches can make the vacuum worse?

I added a few pictures.

[John Futter]

face is more than good enough use a very small amount of apiezon grease on the oring

[Jerry Biehler]

I doubt if you even need any grease. Worse case you can sand any scratches smooth. O-rings are compliant, they dont care too much about flat, sharp scratches are the biggest problem.

[Dennis P Brown]

Before grinding or adding grease, test the item! If it holds vacuum by passing leak tests, nothing further should be done.

If not, trying vacuum grease (following SOP(!) carefully.) As near to no grease as possible is the best amount

If all these methods fail, (and turning on a lathe isn't an option) then grinding can be done by hand. A slow but easy method is to securely mount a fine to very fine Emery cloth (depending on the damage depth) on a very flat metal plate (glass plate on metal works better) and with the edge face down, execute random figure eights on the Emery cloth. The area should be amply large enough to allow this for the throat size of the turbo. Use the finest grade for the final 'grinding". Each step down in paper grade means much longer grinding time. A magnifying glass will allow you to inspect the degree of progress and when to stop.

Never turn the pump so that grit/debris enters the turbo. Holding inverted, clean the surfaces and inter edge before turning back to normal vertical,

[Pascal Mueller]

Of course I am going to test it, I was just wondering how bad such a damage can be - not that I buy something which basically is broken. Also I wasn't able to find a lot information about it.

I guess SOP stands for standard operation procedure?

I have access to the whole machine park of my university. So if I need something they for sure have it somewhere.

Thanks for all the tips! I can't wait to test it - but since exams are coming up I probably won't have time soon. :/