Saturated steam: chamber pressure requirements for autoclave + allowed pressure deviations

Dear all,

I understand that the steam inside an autoclave during the sterilization holding time is crucial to have proper sterilization. Let’s say I run a cycle at 122.5 C. The corresponding pressure to have saturated steam i 2150.86 mbar.

The question is, how much can one deviate from this pressure ± to still have saturated steam conditions?

Thanks a lot for your feedback

As per the HD study it may vary upto +’_15%

Thank a lot for the answer!

What does the HD study stand for? Is it something official?


Heat distribution study

NIST pressure that correspodent to temperature should be less than 50mbars compared to mesured chamber pressure…

Hi @joksavs , I am afraid I don’t understand your sentence completely, could you apply your comment on this specific case: 2150.86 mbar.

Could you tell me what the lower limit and upper limit is (in mbar) to still have acceptable saturated steam conditions? ± 15% (±323 mbar) seems quite a lot to me:

2473 mbar will get you very close to wet steam
1870 mbar will give you very close to super heated steam

Thanks for the feedback,

15% is too wide range for saturated steam. So, my calculation is based on pressure in chamber (in your case 2150mbar) and temperature at the same moment (you did not write that info). Lets say temperature is 122oC.
In this case coresponding pressure to 122oC is 2160mbar. Difference is 10mbars and it is less than 50mbars…its ok to me…

Steam should be at steam boundary phase - and that correlation between temp and pressure … not one pressure value - its depend from temperature…


so I guess that we should assess the pressure e.g. every second to check if it is corresponding to the actual chamber temperature?

But what in case at some point, we have a temperature in the top right corner at 122.7 C, and one in the bottom left corner at 121.9 C? Which pressure should I then use to assess? The difference of corresponding steam pressure is more than 50 mbar…

For info (temperatures with corresponding saturated steam pressure):
121.9 C -> 2110.94 mbar
122.0 C -> 2117.55 mbar
122.1 C -> 2124.18 mbar
122.2 C -> 2130.82 mbar
122.3 C -> 2137.48 mbar
122.4 C -> 2144.16 mbar
122.5 C -> 2150.86 mbar
122.6 C -> 2157.57 mbar
122.7 C -> 2164.30 mbar



we should give evidence that our steam is dry saturated (steam boundary phase). So, steam is saturated or not - and I check that when the situation is stable - at a half of cycle.

I use average temperature of distribution probes and pressure in that moment. Of course taht all HD probes have not the same temp, and because of that I use average. For that temp I find NIST saturated steam table pressure and that pressure compare with measured pressure at a half of cycle.

50mbar is allowed because your instruments have some tolerance.