Best Types of Autoclaves

In this article, the different types of autoclaves are made known. The invention of the autoclave sterilizer is attributed to Charles Chamberland, in 1879.

Around that time, researchers started to understand the advantages of sterile surgery, and doctors needed a more reliable sterilization method than open flaming. The autoclave’s benefits were soon evident, and it became an essential part of every clinic and hospital.

Autoclaves vary in size, shape, and functionality. A very basic autoclave is similar to a pressure cooker; both use the power of steam to kill bacteria, spores, and germs resistant to boiling water and powerful detergents.

Types of Autoclaves

There are different types of autoclaves present in the market, some of which are:

  • Pressure cooker type/ Laboratory bench autoclaves (N-type)
  • Gravity displacement type autoclave
  • Positive pressure displacement type (B-type)
  • Negative pressure displacement type (S-type)
  • Pressure cooker type/ Laboratory bench autoclaves (N-type)

Pressure cooker type

These domestic pressure cookers are still in use in many parts of the world. The more modern type has a metal chamber with a secure metal lid that can be fastened and sealed with a rubber gasket.

It has an air and steam discharge tap, pressure gauge, and safety valve. There is an electric immersion heater at the bottom of the chamber.

Gravity displacement type autoclave

This is the common type of autoclave used in laboratories. In this type of autoclave, the steam is created inside the chamber via the heating unit, which then moves around the chamber for sterilization. This type of autoclave is comparatively cheaper than other types.

Positive pressure displacement type (B-type)

In this type of autoclave, the steam is generated in a separate steam generator which is then passed into the autoclave.

This autoclave is faster as the steam can be generated within seconds.

Negative pressure displacement type (S-type)

This is another type of autoclave that contains both the steam generator as well as a vacuum generator.

Here, the vacuum generator pulls out all the air from inside the autoclave while the steam generator creates steam. The steam is then passed into the autoclave.

This is the most recommended type of autoclave as it is very accurate and achieves a high sterility assurance level. It is also the most costly type of autoclave

Autoclave Uses

  • Autoclaves are critical devices for ensuring the sterilization of materials containing water, which cannot be sterilized using dry heat.
  • Autoclaves are also used for a variety of other purposes.
  • They are used to sterilize media, instruments, and labware as well as decontaminate specific biological waste.
  • Before disposing of regulated medical waste that may contain bacteria, viruses, or other biological materials, it is recommended that it be autoclaved.
  • Autoclaves are used in medical labs to sterilize medical equipment, glassware, surgical equipment, and medical waste.
  • Autoclaves are also used to sterilize culture media, autoclavable containers, plastic tubes, and pipette tips.

Autoclave Operation Procedures

In general, an autoclave is run at 121° C for at least 30 minutes using saturated steam at a pressure of at least 15 psi.

The following are the procedures to be followed when operating an Autoclave:

  • Before using the autoclave, make sure there are no leftovers from the previous cycle
  • The chamber is then filled with a sufficient amount of water
  • The materials to be sterilized are now placed within the chamber
  • The lid is then closed, the screws tightened to ensure airtightness, and the electric heater is turned on
  • The safety valves are adjusted to keep the chamber at the required pressure
  • When the water inside the chamber reaches boiling temperature, the air-water mixture is allowed to escape through the discharge tube, allowing all of the air inside to escape displaced
  • When the water bubbles stop coming out of the pipe, the displacement is complete
  • The drainage pipe is then closed, allowing the steam within to reach the desired levels (15 lbs in most cases)
  • When the pressure is reached, the whistle blows to release any remaining pressure in the chamber
  • Following the whistle, the autoclave is run for a holding period, which is usually 15 minutes
  • The electric heater is now turned off, and the autoclave is allowed to cool until the pressure gauge indicates that the pressure inside has dropped to atmospheric pressure
  • The discharge pipe is then opened to allow air from outside to enter the autoclave.
  • Finally, the lid is removed
  • The chamber is opened, and the sterilized materials are removed

Components of an Autoclave

An autoclave is made up of the following components;

  • Chamber of Pressure
  • Lid/Door
  • Electrical heater/Steam generator
  • Vacuum Cleaner
  • Cooler for Wastewater
Chamber of Pressure:

A steam autoclave’s main component is the pressure chamber, which is made up of an inner chamber and an outer jacket.

The inner chamber is made of stainless steel or gunmetal, and it is located inside the outer chamber, which is made of an iron case.

To reduce the time required to reach the sterilization temperature, autoclaves used in healthcare laboratories have an outer jacket filled with steam. The inner chamber is the container in which the materials to be sterilized are stored.


The lid or door of the autoclave is the next most important component of an autoclave. Its purpose is to seal off the outside atmosphere and create a sterilized environment inside the autoclave. The screw clamps and asbestos washer make the lid airtight.

The lid is made up of a variety of other components, including:

  • The pressure gauge
  • Whistle/Pressure release unit
  • The safety valve

 The pressure gauge

The pressure gauge on the autoclave lid indicates the pressure created in the autoclave during sterilization.

The pressure gauge is critical because it ensures the autoclave’s safety and the operation’s working condition.

Whistle/Pressure release unit

The whistle on the autoclave’s lid is the same as the whistle on the pressure cooker’s lid.

The whistle regulates the pressure inside the chamber by lifting itself and releasing a small amount of vapor.

The safety valve

On the lid of the autoclave is a safety valve, which is critical in cases where the autoclave fails to perform its function or the pressure inside rises uncontrollably.

The valve has a thin layer of rubber that bursts to release the pressure and prevent an explosion.

Electrical heater/Steam generator:

Underneath the chamber is an electrical steam generator or boiler that uses an electric heating system to heat the water and generate steam in both the inner and outer chambers.

The level of water in the inner chamber is critical because if there is insufficient water, the heating system may burn.

Similarly, if the water is present in excess, it may interfere with the trays and other components within the chamber.

Vacuum cleaner:

A separate vacuum generator is present in some types of autoclaves, which pulls air from the inside of the chamber to create a vacuum inside the chamber.

The presence of some air pockets within the chamber may promote the growth of various microorganisms. This is why a vacuum chamber is such an important part of an autoclave.

Wastewater cooling system:

Many autoclaves have a system to cool the effluent before it is used prior to it entering the draining pipes.

This system protects the drainage pipe from damage caused by the autoclave’s boiling water.

Autoclave Safety Precautions

Although autoclaves are fairly simple to use, there are some precautions that must be taken when using one.

Some of the most important precautions to take when operating an autoclave are as follows:

  • Water-proof or water-resistant substances, such as oil or powders, should not be sterilized in autoclaves.
  • The autoclave should not be overcrowded, and the materials should be loaded in such a way that the steam penetrates the articles sufficiently.
  • Autoclavable items should always be placed in a secondary container.
  • To autoclave packaged waste, only autoclavable bags should be used.
  • Articles should be wrapped in something that allows steam penetration to ensure adequate penetration, and materials such as aluminum foil should not be used.
  • Items placed inside the chamber should not come into contact with the chamber’s sides or top.
  • Separate autoclaves should be used for waste and clean items.
  • Attempts to open the lid while the autoclave is in use should be avoided at all costs.
  • Never autoclave liquid components in sealed containers.
  • To prevent the liquid from spilling, only fill the containers to two-thirds of their total volume.
  • Plastic or polyethylene trays or containers should not be used because they may melt and cause damage to the autoclave.
  • Furthermore, do not autoclave flammable, reactive, corrosive, toxic, or radioactive materials, household bleach, or paraffin-embedded materials.
  • Because paper is a combustible substance, it should not be placed directly inside an autoclave. To avoid fire, autoclave it in a waste bag in a bio bag set.

The Autoclaves Principles

The autoclave operates on the moist heat sterilization principle, in which steam under pressure is used to sterilize the material inside the chamber.

Furthermore, the high pressure raises the boiling point of water, allowing for a higher sterilization temperature.

Under normal atmospheric pressure (760 mm of Hg), water boils at 100°C; however, as pressure is increased, the boiling point of water rises.

Similarly, high pressure facilitates the rapid penetration of heat and moisture into deeper parts of the material and the moisture in the steam causes protein coagulation, resulting in the irreversible loss of function and activity of microbes.

This principle is used in an autoclave, where water boils at 121°C under a pressure of 15 psi or 775 mm of Hg.

When this steam comes into contact with the surface, the latent heat it emits kills the microbes. The moist killing of microbes is ensured by the condensed liquid.

When the sterilization phase is finished (depending on the level of contamination of the material inside), the pressure inside the chamber is released through the whistle.

The pressure inside the chamber is then returned to normal while the components remain hot for some time.


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