The autoclave is not a vacuum internally while in operation. The term "vacuuming" generally refers to the vacuuming process before heating, as the autoclave itself uses steam as a heat source for steam curing and thus operates under non-vacuum conditions. The primary purpose of vacuuming in the autoclave is to evacuate any remaining steam and water vapor inside, ensuring the autoclave is sealed, and to remove the volatile water from within the autoclave.

The specific operation of vacuuming a steam autoclave involves using a vacuum pump to remove the vacuum inside the autoclave during the steam curing process. Generally, this can be completed in about half an hour. After vacuuming, the autoclave approaches pure steam pressure. The vacuuming is not only for heat transfer but also to allow steam to better penetrate some construction materials being cured in the autoclave, enabling the heat within the autoclave to be transferred more quickly and effectively to the materials, accelerating the heating speed and shortening the heating time, which is beneficial for temperature equilibrium. However, for the heating process of the autoclave, we still need to proceed slowly to achieve an even effect.