autoclave: principle, working and construction




  • Autoclave is a machine used in industrial and scientific process which require high pressure and high temperature
  • Autoclave provides a physical method for sterilization by killing bacteria, virus even spores by the means of steam under pressure.
  • It sterilizes the materials by heating them up at a particular temperature for a specific period of time.
  • It is considered as more effective method of sterilization based on moist heat sterilization,

Principle and working:

  • Autoclave work on the principle of moist heat which uses steam and pressure inside the chamber for sterilization.
  • The boiling point of water is 1000 C under atmospheric pressure (760 mm of Hg), high pressure in autoclave increases the boiling point of the water to achieve proper sterilization.
  • In addition high pressure facilitates the penetration of heat into the microbial cell and moisture helps in the coagulation of the protein cause death of the microbes.
  • Working temperature of autoclave is 1210 C at the pressure of 15 psi or 775 mm of Hg.
  • Steam comes in the contact with the surface of the material inside the chamber and kills the microbes by giving latent heat.
  • After completion of the sterilization the pressure is released from the whistle and the chamber is restored back to the ambient temperature.

Autoclave components/ parts:


  • It is the main part of an autoclave consist of inner chamber and outer jacket
  • Inner side of the chamber is made up of stainless steel or gunmetal and the outer side is made up of iron
  • A healthcare laboratory uses the autoclave which has an outer jacket filled with steam to reduce the time taken for the sterilization.
  • Size ranges from 100 L to 3000 L .


  • It is the next important part of an autoclave. A lid is used to seal the chamber and create sterilize condition inside the autoclave.
  • Lid having rubber seal to make chamber airtight, screw clamps are also used.
  • It consists of various other components

Pressure gauge:

Pressure gauge is used to indicate the pressure created inside the chamber. It ensures the safety of the autoclave while operating.

Whistle/ pressure releasing unit:

It is present on the lid, work of the whistle is to control excess pressure by releasing it.

Safety valve:

It is important part because it is used in case when autoclave failed to work properly and continuously increasing pressure. It contains a thin layer of rubber inside it that burst itself to release pressure and avoid and damage.

Electric heater:

  • An electric heater in present underneath the chamber which is electrically operated and boils the water and produce steam inside the chamber.
  • Water level in the chamber is vital as if chamber doesn’t have sufficient water the heating element might be burnt and if there is too much water in chamber it could interact with trays and material kept inside it.

Waste water cooler:

  • Many autoclaves come with cooling system which is used to cool the hot effluent into the drainage.
  • Used to prevent any damage to the drainage pipe from hot water.   

Procedure of running:

  • Before every operation autoclave should be checked for any item left from previous operation
  • Water level should be checked if needed add sufficient water.
  • All the material to be sterilized place inside the chamber.
  • Close the lid and tightened the screw and safety valves  to ensure airtight condition and switch on the heater.
  • Once the water boils the chamber is allowed to release the mixture of air and water from the discharge tube to ensure only moisture inside the chamber. The complete displacement is observed once  the bubbles cease to come out from the tube
  • Now let the steam allowed to reach the desirable pressure (15 lbs).
  • Once the pressure reached to its desired level the excess pressure is released by the whistle. After the first whistle the autoclave run for holding period i.e. 15 min.
  • After the completion of holding period the heater is switched off and leave autoclave to cool down until the pressure gauge indicate the pressure inside the chamber equals to atmospheric pressure.
  • Discharge pipe is now opened to allow air inside the chamber and lid is opened, sterilized material are taken out from the chamber.

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