I have a vacuum that shows a max vacuum gauge reading of 23"Hg when connected to a chamber. When placing room temperature water inside vacuum, the water doesn't boil. I have seen this chart before https://www.engineersedge.com/h2o_boil_pressure.htm which indicates that my vacuum pressure is not enough to boil the water at room temp. The chart states that I would need a vacuum pressure of about 29.12 "Hg to boil water at room temp. I understand this. However, I have seen multiple videos of people using water inside a syringe and being able to adjust the pressure (by adjusting the plunger) enough for the water to boil without the need of a powerful vacuum. How is this possible?


  • 1
    $\begingroup$ Does the vacuum gauge reading of 23"Hg mean that your chamber is at a pressure of 23"Hg, or does it mean that your chamber is at a pressure that is 23"Hg below atmospheric pressure? $\endgroup$ – probably_someone Sep 5 '18 at 21:27
  • $\begingroup$ Are you sure that the syringes in the videos didn't contain $warm$ water? $\endgroup$ – Philip Wood Sep 5 '18 at 21:43
  • $\begingroup$ @PhilipWood I always use alcohol. It's much more dramatic. $\endgroup$ – JEB Sep 6 '18 at 0:44
  • $\begingroup$ I'm going to guess that you have only a mechanical pump, and that you don't have a high precision gauge to tell you how good your vacuum is. $\endgroup$ – dmckee Sep 6 '18 at 14:17
  • $\begingroup$ @probably_someone The chamber is at a pressure of 23"Hg below atmospheric pressure. $\endgroup$ – N. G. R. Sep 10 '18 at 14:38

Remember that boiling is a phenomena in which the liquid is no longer in equilibrium with its vapor above the surface. If there is already an equilibrium, you won't see the common occurrence of boiling.

  • 1
    $\begingroup$ This is true, but without discussing the relationship between the quality of the vacuum and the vapor pressure of water it is rather incomplete and probably dosen't help the OP a lot. $\endgroup$ – dmckee Sep 6 '18 at 14:15

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.