The Mason Jar Vacuum Chamber

The following is actually a piece to a larger project of mine, but that one's ongoing and requires more tweaks and research. The important thing here is that I needed a vacuum chamber, and on an exceedingly low budget. Thus began my quest! For the pump, I used a refrigerator compressor, Mother Earth News has a nice page about that here.

The few vacuum chambers that I found online were good, and in some cases better than mine, in terms of size and ease of use, but were still just outside my budget. Time was of the essence, what with spring semester looming, so I ended up with a mason jar vacuum chamber.



I wanted my vacuum chamber to be easy to clean, non-reactive, and transparency would be a bonus for observation. The jar seemed like a natural choice! I would have applauded myself for originality, but Google will give one over 9,000 results if one searches for "mason jar vacuum chamber". I will instead assert that this idea is underrepresented, as I'm very happy with the results, cost, and potential for reconfiguration or expansion of the apparatus.

Conveniently, the only modification that had to be done here was the lid. When I harvested my compressor, I left as much of its original copper tubing as reasonably possible, and ended up using sections of pipe as my jar inlet and outlets.

I drilled a hole slightly smaller than I needed and used a Dremel to widen the hole just so my pipe would have a snug fit. The lid is pretty flimsy, so be sure to use light pressure when drilling, my first few attempts tore the lid in addition to making a hole. Then, armed with a torch and some solder, I made my first lid. Later on I added another hole for a relief valve or a vacuum gauge that I had ordered a few weeks prior.

Here it is!

When soldering the lid, I learned a couple things:
 - Take care to only aim your torch flame at your copper pipe near its top, and not on the lid itself, the white underside of the lid will scorch(or in this case, the top, too)
 - Don't place any holes which need to be soldered too close to the edge, as you can mess up your seal that way, as shown here:

It still sealed a little bit, and for initial testing it was all I needed, but I ended up making another set of lids for the version I'd actually be working with. A pack of 12 jar lids at a local grocery store only set me back a little under two dollars, so experimentation and reconfiguration has minimal cost. I will add that one should use lead-free solder if anything in the vacuum chamber is to be consumed, just to be on the safe side. It's a little harder to work with, and you'll have to buy some flux to get your joints to turn out right. Refer yourself to any of the multitude of guides on soldering copper pipe if you go that route.

I was happy to find that the pipe thread on the spare valve I had(from a cheap espresso machine) and on my gauge would make a good seal. I just made sure the hole was only just big enough for the threads, and I used plumber's pipe thread compound on the threads themselves.

So finally I ended up with a lid that had a valve, a vacuum gauge, and my bit o' pipe. Some tubing and hose clamps finished the whole thing off, and I can pull a pretty nice vacuum.

No scorching or anything!

Although, if my gauge is to be believed I've managed an absolute pressure of less than zero!

It's a cheap gauge, and it did take a minor spill earlier - it now insists that atmospheric pressure is 4 psi below atmospheric pressure. I am dubious of its claims.

Here's a video of the thing in action:

I got some 90 degree water to boil, but nothing with a lower temperature than that. This suggests, according to some tables in my thermodynamics book, an absolute pressure of around 0.7 psi, or a gauge pressure of -14 psi. It's more than enough for my project, but I was a little disappointed I couldn't reach a pressure low enough to sublimate ice. I'll probably do some work to improve this in the future, and it does seem that people have made diy diffusion pumps before, I may give that a shot. For now, this thing does what I need it to, so if it ain't broke, I'm not gonna fix it.

Hope you've enjoyed this as much as I have, which is to say, a lot. Having a vacuum chamber is fun!

 - Colton