Paint tank pressure chamber conversion. Help appreciated.

[Fleafa]

2-part RTV Shore 18 Silicone
Very happy, thought the teardrop by the heart needs to be sharper. That's a problem with the original sculpt though. The formers were printed by in their Frosted Ultra Detail material, by the way. Very nice.
The symbol is for the space marine chapter, the incredibly unlucky successors to the already very emo Blood Angels. Commission for a friend.

[Fleafa]

Casually looking into vacuum pumps at the moment and it is proving difficult to find the info I need on the ones I can afford. Always the case, it seems!
is dirt cheap for a new pump but only pumps 1CFM. The quoted max. vacuum is 10Pa, which I understand to be in excess of the 29 micron requirement I hear mentioned. However, is it likely to reach that in any practical timeframe?
pulls 3CFM but also lists 10Pa.
Also, and actually lists 75 micron.

HELP!!!!

[mangozac]

Paulson has been going through some vacuum pump investigations recently so hopefully he will chime in. Personally, I would not get anything less than 3CFM if you're using a standard 10L pressure pot. Looking at I think 75 microns would be OK. For the record my old vacuum pump will generally only go to -28 inches of Hg, which is around a whopping 50,000 microns (but I don't rely on the vacuuming alone to remove all of the bubbles).

I'm not sure it's a 29 micron requirement you hear about rather than 29 in/Hg (inches of mercury), which is around 20,000 microns.

So bottom line: I reckon any pump that will go to less than 1000 microns and greater than 3CFM will do the job fine.

[Fleafa]

Riiiight... OK, thanks. Was thinking numbers weren't adding up...
So hard to get good info on this. Microns is apparently not the standard way to measure a vacuum though it is used a fair bit. Most pumps I see don't qualify the max vacuum attainable. They are generally AC or refrigerator pumps, so maybe there is a specification which is common to these applications..?


...also; I think I was reading that table upside-down earlier today!
Reading it now, 10 Pa looks OK.

[Fleafa]

I have a friend who works for Rolls Royce and was able to acquire a venturi pump along with various fittings. Using my compressor it pulls about -25", which will do for now. In theory, it should manage more. Not sure why it only does -25". Will be posting some of my projects soon.

[mangozac]

In theory as in your compressor's constant flow rate is enough to provide better than -25"?

I did investigate a venturi device when I was looking at vacuum pumps but I concluded that it would be hard to get consistent results with it.

[Fleafa]

It *should* be, though the 6.5 Bar at which the pump is most efficient is a little beyond it for a long enough period.