From itattooz wiki
Basic form of autoclave is pressure cooker. To create steam water is heated in a pressurized environment. Pressure used to heat to higher temperatures with less energy. For removing air prior to pressurization autoclaves have various configurations. Autoclaves are usually made of steel. Autoclaves use gravity to remove air. For reach optimum pressure autoclaves use pulses of steam along with pressurization and depressurization. For pressurization vacuum pump autoclaves suck air out. Great atmospheric autoclaves are a combination of steam pulsing Vacuum pump techniques.