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Different Kinds of Autoclaves

An autoclave is a special device used in hospitals, science labs and other places to sterilize various equipment. It kills bacteria by applying extreme heat and steam to anything placed within the autoclave chamber after the chamber has been made into a vacuum. Autoclaves are also known as "steam sterilizers" because they all use steam as an effective sterilization agent. However, there are numerous kinds of autoclaves, all of which differ slightly in the method by which they sterilize instruments.

Negative Pressure Displacement Autoclave
- The negative pressure displacement autoclave is one of the more reliable sterilization devices, but it is also among the most expensive. This type of autoclave works by removing all the air from the main chamber with a vacuum pump. Steam is created in a second, hidden chamber within the device and is released into the chamber in a quick blast that works to sterilize any remaining bacteria. Negative pressure displacement autoclaves are "Type S" devices; they first create a vacuum in the main chamber to remove any airborne contaminants.
Positive Pressure Displacement Autoclave
- Positive pressure displacement autoclaves work similarly to their negative displacement brethren, but they do not remove the air via a vacuum pump first. These autoclaves may also be called "gravity" autoclaves. They simply build up enough steam in one chamber to displace all the air in the main chamber and then fire the air in with a quick blast. The steam "displaces" the air, which is pushed out through a one-way vent. This is an example of a "Type N" autoclave, which does not create a vacuum first.
Multi-vacuum Autoclaves
- Multi-vacuum autoclaves work like negative pressure displacement autoclaves. They essentially do the exact same thing: They create a vacuum and then apply highly-pressurized steam. However, to ensure maximum sterilization, the multi-vacuum autoclave will repeat the process several times. It will suck out any steam to create a vacuum and then apply more steam. This ensures that any bacteria that may have survived one blast is taken care of with subsequent blasts. These types of autoclaves are also known as "Type B" autoclaves.
Downward Displacement Autoclaves
- Downward displacement autoclaves are among the least expensive and are often used in high school or college science labs. They use water and a heating element at the bottom of the chamber to slowly fill the space with steam. The steam gradually pushes the air in the chamber out through a vent at the bottom. The vent is closed when the temperature in the chamber reaches a proper sterilization point and most, if not all, of the air has been removed.

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