I have a vacuum chamber that I would like to backfill with 15 mTorr of argon. The problem with accomplishing this is that most pressure regulators can't do pressures that low. Are there regulators that accurately regulate mTorr level pressures, or is there some other approach to backfilling a vacuum system at low pressure?

  • $\begingroup$ if you know the volume of the chamber, then connect it to another chamber with the argon in it at a suitable pressure, temperature and known volume . when you open the valve then the pressure should equalise to the value you want .... $\endgroup$ – Solar Mike Oct 19 '17 at 10:35
  • $\begingroup$ i would assume your chamber is already instrumented to monitor the vacuum. use that to feed back to a valve. That said there are undoubtedly off the shelf systems to do exactly what you want. $\endgroup$ – agentp Oct 20 '17 at 11:18

The simplest way to do this would be to design your own.

A commercially available spring, with an OD of 9mm, a length of 19mm, and a wire dia. of 1mm has a rate of 3.15 N/mm, with 11.5 mm compression length. Putting the lowest possible regulator in front of your homemade regulator, set a large diaphragm across a 1m diameter expansion chamber.

Then, place this commercially available spring on both sides of the diaphragm. At 15 mTorr, the springs should deflect a controllable 0.5 mm, which could be used to regulate the poppet valve. The key is a very large expansion chamber and a very small spring with a highly precise spring rate. To prevent the spring from moving, the expansion chamber will need to be evacuated, and the small springs need to be placed carefully to ensure the edges do not bind, but they do not collapse or buckle. This shouldn't be a problem, as the springs are well designed, but it's something to keep in mind when designing the expansion chamber.

  • $\begingroup$ doesnt this depend on the external pressure being regulated to extreme high precision? $\endgroup$ – agentp Oct 20 '17 at 11:25
  • $\begingroup$ That’s the point of the large expansion chamber - to multiply the very tiny forces to something measurable. It’s also the point of the small and sensitive spring, so they can translate those still small forces into something that can be regulated. A screw can easily turn 0.5mm of linear movement to a wide range of forces. $\endgroup$ – Mark Oct 20 '17 at 13:30
  • $\begingroup$ I don’t see a meter diameter wide regulator being an item that comes to market. The major instrument suppliers in California don’t seem to offer anything larger than a few mm diameter. $\endgroup$ – Mark Oct 20 '17 at 13:32

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