I’m trying to size the right vacuum pump for a 2l and a 5l. Spd. I’ve found that although many pump say they pull down to 29 hg when they get here they only pull 25. I’ve read through many threads here and haven’t been able to find a thread spewing out the different size pumps to flask size ??? Anyone have good rule of thumb?

You need a consultant or you need to do some more research on this forum

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Any threads you could point me to?

It’s not the number on that guage you want to look for. It’s ultimate micron

Look into the adixen/Alcatel 2021


There are a number of factors that could be causing your low vac, you may have a leak!


Are you at high elevation

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The Alcatel looks like the cam and micron rating is good for a 5l. But would you use that for a 2l as well?

I’m at 5000 feet

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You cant get to -29.9 @ that elevation. Height Above Sea Level Chart


That’s why you are only getting to 25. Roughly every 1000 feet in elevation, you lose a psi of vac. You’re already under vac from atmospheric pressure.

That Alcatel is great for a 5l, why wouldn’t it be great for a smaller unit?

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Ahhh. So is 25 a full or ultimate vacuum at this altitude? I’m running both at the same time and wasn’t sure I needed that big a pump for the 2l

You want a guage that reads in microns; hg is more relevant for your closed loop or vac oven where ultimate vacuum depth is not needed. You are looking to be in a hard vacuum and to monitor it closely. You’re gonna want a secondary pump for getting through the stank. Or a lot of pump oil

That pump would be great

I was getting to the thread on using two pumps together. Not trying to cheap out but understand the capacities of these pumps…

If you have a Alcatel rated 15 cfm pulling down to under 100 microns. It will do a 2l or a 5l. Will it do a10l or more? Is there a more size “appropriate” pump for a 2l? Or is one size fits alll and that’s a large pump…

Is there a vapor pressure/cfm rule of thumb?

That pump is perfect for up to a 5l, it couldn’t handle much bigger without help.

That pump is perfect for your 2l. There’s guys on here that use it for 1l and 500 ml units.


The 2021i sounds like your ticket. Also you’ll need to do a leak down on your system and get a gauge that at least uses an agilent 531 gauge like a bullseye or yellow jacket handheld that reads down to 1 micron

Yes a alcatel will work on a 2l and a 5l. There only 14cfm sonif your using gl connections the mist you dan pull is about cfm. Ive used alxatel for a long tine there a good cheap pump to get started with

Ok. Just to confirm. At my altitude 25 hg or roughly 100,000 microns is a full or hard or ultimate vacuum?

For spd. If you can get under 300 you can make it work. During main if you can get under 100, you’re solid.