Originally posted by @fabianfnas
ISS took a leak in space...
Drum roll, laughter from drunken audience😉
BTW if nobody heard of Torr Seal, it is an epoxy specially designed to not be permeable to gasses used in a vacuum system where for instance, instead of using that you used plumbers putty which could be a temporary solution but some small amount of air would diffuse through the putty which would mean there would still be a slow (MUCH slower) leak but a leak nonetheless.
Torr Seal epoxy is designed to neither emit its own internal gasses or allow diffusion through its own material. It would be more like someone doing a welding job of pure steel or aluminum.
In the vacuum system world, there are several ways to prevent leaks, one common one is just an O ring clamped to a properly fitted holding device, a clamp ring.
Most people use an O ring grease, an atomically thin layer of vacuum grease to help the O ring seal to possible roughness in the metal O ring clamps, one such is called Apiezon grease, a very high (several grades in fact) of diffusion rate greases.
I worked at an IBM facility where the engineers there said if you need Apeizon or some such O ring grease there is something wrong, the material of the O ring itself should be able to make a good seal.
But most vacuum folks would take some Apiezon O ring grease and coat the O ring with a thin layer so microscopic roughness in the clamp rings would be filled with that tiny bit of grease.
Apiezon grease is specially formulated to not allow the diffusion of air across just the grease interface and there are some of these greases much better than others in that regard so you have to tailor the grease to the expected value of the vacuum being used.
In my semiconductor machine applications, we may get down to minus 8 torr range which for most semiconductor work is a decent but not perfect vacuum.
Apiezon has a diffusion rate that goes down at least ten times better than that so for such vacuum systems Apiezon works well.
However, there are other vacuum greases like those made by Dow corporation that can work with mechanical vacuum pumps just fine but would allow enough diffusion to spoil a minus 8 level vacuum, causing a permanent slow leak but that would be fine for a roughing pump which operates down to the micron range, like a few millitorr of pressure, where such Dow company greases work just fine.
But for the highest vacuum levels like what is needed for particle accelerators even Torr Seal would be like an open door so they have to use solid metal compression seals where there is a MUCH MUCH lower level of diffusion through vacuum joints so they can get down to minus 12 Torr levels or better. I think the air around ISS is around minus 14 Torr or so, much better than even the best particle accelerators and I envision particle accelerators on the moon for instance where all the guts are just out in the open.
Accelerator magnets and beam lines and such never needing the massive casings used in any vacuum system regardless of the Torr level achieved so an accelerator on the moon would be a LOT cheaper and a LOT less mass than anything on Earth. Just an aside😉