When we think of a vacuum leak we generally think of a car that just doesn’t want to run quite right. Most normally aspirated internal combustion engines rely on the vacuum created by the pistons to draw in the air fuel mixture that’s produced by the carburetor or fuel injection system. Identifying the leak usually involves spraying something combustible around common trouble areas while the engine is running. Changes to the engine speed indicate when the combustible gas enters the intake manifold and the leak can be found.

What if your vacuum leak is in a highly specialized piece of scientific equipment where the pressures are about 12 times lower than atmospheric pressure, and the leak is so small it’s only letting a few atoms into the vacuum chamber at a time? [AlphaPhoenix] takes dives deep into this very subject in his video “Air-tight vs. Vacuum-tight.” which you can watch below the break.

Not only does [AlphaPhoenix] discuss how a perfect pressure vessel is sealed, he also explains the specialized troubleshooting methods used which turn out not to be all that different from troubleshooting an automotive vacuum leak- only in this case, several magnitudes more complex and elemental in nature.

We also enjoyed the comments section, where [AlphaPhoenix] addresses some of the most common questions surrounding the video: Torque patterns, the scarcity of the gasses used, and leaving well enough alone.

Does talking about vacuums get you pumped? Perhaps you’d enjoy such vacuum hacks as putting the toothpaste back in the tube in your homemade vacuum chamber.

Thank you [Morgan] for sending this one in. Be sure to send in your own hacks, projects, and fantastic finds through the Tip Line!

15 thoughts on “Solving Ultra High Vacuum Leaks Has An Elementary Solution”

1. Tim says:
   August 16, 2021 at 8:07 am

   “about 12 times lower than atmospheric pressure” Maybe should be about 12 orders of magnitude lower?

   Reply
   1. Töm says:
      August 16, 2021 at 8:27 am

      Sorry, not the same thing.

      Reply
      1. Pruttelherrie says:
         August 16, 2021 at 9:07 am

         I believe that was exactly Tim’s point. 1/12th of atmospheric pressure is peanuts, 10^-12 of atmospheric pressure is ultra-high vacuum.

         Reply
         1. Comedicles says:
            August 16, 2021 at 9:18 am

            What is the lowness of atmospheric pressure? We can agree that X times lower = divide by X. Or we can agree it it is a syntax error and treat it like dividing by zero with a “don’t do that” warning.

            (Chasing vacuum leaks has been the primary occupation of many a physics grad student.)

            Reply
2. Roger says:
   August 16, 2021 at 9:07 am

   Very interesting video.

   Two things did surprise me as the repair was being completed:

   1.) You weren’t using a torque wrench to get all of the bolts torqued down to the same tightness.

   2.) You just went around the outside of the flange in order instead of tightening in a pattern that tightens bolts in a more diagonal pattern. Something like tighten the first bolt, move to the bolt 180 degrees away then move to a bold 90 degrees from that and then 180 degrees. This results in more even pressure on the flange and gasket surfaces.

   Reply
   1. Johnson says:
      August 16, 2021 at 9:30 am

      Yeah, i don’t know, star pattern is the first thing I learned when working on automotive stuff, as well as when a torque wrench is appropriate. In this case he should be using both, for the most reliable fitment. But what do I know, I’m a rando on the internet.

      Reply
   2. Pat says:
      August 16, 2021 at 9:34 am

      Note that in the body of the article, it says:

      ” where [AlphaPhoenix] addresses some of the most common questions surrounding the video: Torque patterns,”

      Granted, going through YouTube comments is like searching a trash heap, so I’ll help you out, where he replies:

      “I think I’ve replied in more detail somewhere but as this is a top comment I’ll post here too. I was originally taught that you want to “cut in” the knife edge on these copper gaskets continuously, by tightening slowly in a circle, so that’s how I’ve always done it. That said, I know a lot of people that cross-tighten the whole way and also normally don’t get leaks – a great deal of vacuum science seems to be black magic and superstition. If a procedure works well enough, you stick with it, which unfortunately ends in a lot of competing-but-effective methods.”

      Reply
   3. Pat says:
      August 16, 2021 at 9:37 am

      Also, the comment re: torque wrench was:

      “Regarding the torque wrench, in many many locations on this system, it’s almost impossible to fit a regular wrench around these flanges, let alone a necessarily bulkier torque wrench. This flange probably could have been handled by an open-end torque wrench, which I guess I assume exists but have never seen, but in general to work on these academic systems you need to develop a feel for it. Notice how I’m barely moving the wrench with each tighten.”

      As someone also in academia, I can *totally* understand the “just get a feel for it” problem due to one-off builds with too-tight clearances.

      Reply
   4. macona says:
      August 16, 2021 at 9:45 am

      So doing the thing where they are not tightening can often come back to bite you in the rear when working with conflats. Spec is you tighten them till the flanges meet. Torque does not matter and you generally just work your way around the flange, there is not torque pattern like a wheel hub or engine head. The knife edges dig into and deform the copper and the the groove is designed so that when they are flat against each other they copper deforms and take up the space. Generally if it leaks after you tighten them up either you got come crud where the knife edge is or someone dinged the knife edge which is generally unrepairable. If you have access to a machine shop you can recut the flange if you can mount it in a lathe.

      Reply
3. PWalsh says:
   August 16, 2021 at 9:35 am

   I’ve done some of this.

   The interesting bit about vacuum is “mean free path”, which is the distance something will travel in your chamber before hitting a molecule.

   So if you want to make an electron microscope, if the mean free path is less than your beam length, chances are that a lot of the electrons will collide before they reach the target (or collide after reflecting off the target).

   Medium vacuum, something you can get with a single vacuum pump, about 1.0 to 10^(-3) torr, is in the range of a couple of inches. That’s good enough for sputtering, but not enough distance for the electron microscope, and not enough for many applications.

   The Wikipedia article has a nice table in the middle that shows the mean free path by type of vacuum.

   https://en.wikipedia.org/wiki/Mean_free_path

   Once you are below medium vacuum, the molecules are so rare that they (statistically) stop acting like a gas. You have to start using kinetic means to remove individual molecules.

   Reply
   1. macona says:
      August 16, 2021 at 9:48 am

      I mean with sputtering you have to have gas in there for it to work! On the machine I built we pumped down as low as we could go with a turbo and then backfilled with argon.

      One interesting thing about electron microscopes is that during operation there is usually only one electron traveling down the column at any time. Kind of like a drip coffee maker.

      Reply
4. Donald Vaughn says:
   August 16, 2021 at 9:36 am

   This is interesting since I regularly work with vacuums down to low 10^-7 torr and our problems while similar are no where near as difficult, I.E. viton O-rings vs. knife edge seals. This makes my job seem less miserable when hunting leaks!

   Reply
5. Col. Panek says:
   August 16, 2021 at 10:10 am

   General Electric’s Glyptal enamel was the leak sealer of choice for our big radar tubes. Then an ion pump brings it down to where the tube will work again.

   Interestingly, those tubes sent up to space still needed envelopes and couldn’t use all that free vacuum, because it was poorer than what we achieve on earth. Satellites have lhin little clouds of gas that float along with them.

   Reply
   1. Rumble_in_the_Jungle says:
      August 16, 2021 at 12:08 pm

      Now that is the type of comments, I still look for on this site. Thanks for the fascinating info!

      Reply
6. Clara Listensprechen says:
   August 16, 2021 at 10:17 am

   Ya, I’ve worked with high vacuum in sputterers, plasma ashers and electron gun milling where the vacuum is measured in terms of torrs and not in terms of inches of mercury column, and the pumps were either cryo or lobed rotary. No copper sealing was used, just large o rings that, when cleaned with alcohol, needed to be thoroughly dried out before reuse or the alcohol would outgas and indicate a leak when there wasn’t one (could be eventually pumped down but with a lot of extra time involved). Torquing down involved first simple hand tightening initially then gradually in round sequence rather than automotive star pattern. The big trick was taking it apart where if you loosened one side too much you couldn’t get the opposite bolts loose at all. I had to rescue a greenhorn maintenance tech who did that when he complained that he needed to drill a bolt out of the hole because it absolutely would not come loose. I re-torqued all the bolts, undid each one by the same method they were tightened, and all the bolts came out easily.

   Reply

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