Autoclave 101 - What Is It And How Does It Work?

What is an Autoclave and How Does It Work?

Autoclaves, also synonymously known as steam sterilizers are typically used to carry out healthcare or industrial applications requiring elevated steam pressure and temperature. An autoclave is a simple machine that makes use of pressurized steam to kill and destroy microbial life that may be present on a contaminated load placed inside the pressure vessel including harmful bacteria, viruses, fungi, and spores.
Picture of a manual autoclave for demonstration purposes
(Picture of Tuttnauer autoclave above)

A load is considered sterile once it has undergone a full sterilization cycle, upon which it can be reused for sensitive areas such as laboratories or operating rooms without the fear of introducing foreign microorganisms. Different types of items must be sterilized for different lengths of time and at different temperatures to reach the desired state of sterility.

 Table of Contents 

1. A brief history of the autoclave.

2. Why does steam work for sterilization?

3. How does an autoclave work?

4. Important parts of an autoclave.

5. How to use an autoclave?

6. When to use autoclave?

7. Precautions while using autoclave.

8. What is the difference between manual and automatic autoclaves?

9. Which autoclave should I choose?

A brief history of the autoclave

The autoclave used today has been intimately modelled after the “steam digester”, a prototype invented by physicist Denis Papin in 1679. This autoclave was essentially a modern-day pressure cooker and was founded to process food for easier digestion. It wouldn’t be until 1879, two centuries later that French microbiologist Charles Chamberland would create a new version of the autoclave to be used for medical applications.

Over time, new autoclave technology emerged, giving way to pre-vacuum cycles or steam-flush pressure-pulse to create the autoclave popularly used in the hospitals today. Despite the change in design and new additional features, the principles and methods for sterilization have, to a large degree, remained unchanged for the past 150 years.

Why does steam work for sterilization?

The basic principle behind this phenomenon is that moist heat destroys cells and microorganisms. Steam is a very efficient medium for heat transference while air, on the other hand, is ineffective in transferring heat and energy because of a concept called the heat of vaporization.

When steam comes on contact with a cooler object, it condenses into water and transfers all of the energy (needed to boil and steam the water) onto the cooler surface. This process heats up the microorganism cells with higher efficiency than would air and at an adequate temperature, causes the cell walls to breakdown and undergo irreversible coagulation. Due to the denaturation of enzymes and structural proteins that make up a microorganism’s cell, we can achieve successful sterility through steam.

(Example of steam sterilization below)
Example of steam sterilization inside of an autoclave

 

How does an autoclave work?

Irrespective of whether it is a small tabletop unit or an industrial-sized bulk unit, all autoclaves operate using principles similar to those of a kitchen pressure cooker- that is, the chamber is sealed and all air within is replaced by steam.

Three factors are critical to ensure successful steam sterilization in an autoclave- time, temperature, and steam quality. To meet and execute these requirements, there are three phases to the autoclave process:

  1. Conditioning Phase (C): Air inhibits sterilization and must be removed from the chamber. Steam flows through the sterilizer and starts to displace the air within the chamber.
  2. Exposure Phase (S): After the air is removed, the sterilizer drain closes, and steam is continuously admitted into the chamber. This program rapidly increases the pressure and temperature inside to a predetermined setpoint and maintains them until the desired time is reached. The items are exposed to the steam and allowed to sterilize.
  3. Exhaust Phase (E): The sterilizer drain is opened and steam is allowed to exit, depressurizing the vessel and allowing the items in the load to dry.

Under appropriate pressure and temperature, the steam can reach in even the smallest of crevices and can kill a vast majority of the microorganisms, making the item fully sterile and ready for reuse.

Important parts of an autoclave

  1. Vessel: The vessel is the main body of the autoclave, consisting of an inner chamber and an outer jacket. Hospital autoclaves come with jacketed chambers where the jacket is filled with steam, effectively reducing the duration of a sterilization cycle. The jacket improves temperature uniformity within the chamber, reduces the likelihood of wet packs, and minimizes wet steam detrimental to the sterilization process.
  2. Thermostatic trap/whistle: A thermostatic trap or steam trap is a device designed to allow air and condensed water to escape from the chamber while preventing the passage of dry steam.
  3. Safety valve: Fitted with a number of safety features, the safety valve is the final fail-safe device for the pressure vessel in case all electronic controls fail.
  4. Steam generator: A steam generator or boiler is present underneath the chamber. It uses an electric heating system to heat the water and generate steam in the chamber.
  5. Vacuum generator: In some autoclaves, a separate vacuum generator is present to pull the air from inside the chamber and expel it outside, creating a vacuum inside the chamber.
  6. Waste-water cooler: Many autoclaves are equipped with a system to cool the effluent before it enters the draining pipes. This prevents damage to the draining pipes due to the boiling water.

How to use an autoclave?

In general, items to be autoclaved are subjected to a gradual temperature increase up to 121°C and then steamed for around 15 to 20 minutes, under radical pressure of 15 psi. The steam used should be composed of 97% steam (vapor) and 3% moisture (liquid water).

Here is how you can operate an autoclave with ease:

  • Add a sufficient amount of water inside the chamber.
  • Place the materials to be sterilized inside the chamber.
  • Close the lid and tighten the screws to ensure than an airtight condition is created. Then, switch on the electric heater.
  • Adjust the safety valves to maintain the required pressure in the chamber.
  • Once the water begins to boil inside the chamber, the air-water mixture should be allowed to escape through the discharge tube so that all the air inside the chamber can be replaced by steam.
  • Once all the air has been displaced by steam, water bubbles will stop coming out of the pipe and you can now close the drainage pipe.
  • The pressure within is allowed to reach the desired level of 15 psi. Once the pressure is reached, the whistle blows to remove excess pressure from the chamber.
  • After the whistle goes off, the autoclave is kept running for a holding period of 15 minutes.
  • The electric heater can then be switched off and the autoclave is allowed to cool until the pressure gauge indicates that the inside pressure has lowered to that of the atmospheric pressure.
  • Open the discharge pipe to allow air from outside to enter the autoclave.
  • Finally, open the lid. The sterilized materials can be taken out of the autoclave.

When to use autoclave?

Autoclaves can be used for a variety of medical applications such as:

  1. To decontaminate medical waste containing bacteria, viruses, and other biological materials before disposal.
  2. To sterilize medical equipment including glassware, unwrapped goods, utensils, porous materials, surgical equipment, etc.
  3. To sterilize culture media, autoclavable containers, plastic tubes, and pipette tips.

Because autoclaving sterilizes items without the use of reagents, it allows for the reuse of many lab equipment and supplies. It is, for this very reason, opted as an environmentally friendly method of sterilizing medical waste before disposal without the need for incinerators.

Precautions while using autoclave

Although fairly easy to use, you should be aware of some of these rules while operating an autoclave:

  • Autoclaves should not be used to sterilize water-proof or water-resistant substances such as powders or oils.
  • Should not be overcrowded, instead, the items should be loaded in a way where all of them receive sufficient penetration by steam.
  • Only autoclavable bags should be used to autoclave packaged waste.
  • Materials like aluminum foil should not be used to wrap articles for effective penetration by the steam.
  • All items should be placed in the chamber in a way that they do not touch the sides or the top of the chamber.
  • Waste and clean items should be autoclaved separately.
  • The autoclave should not be opened while it is working.
  • Liquid components should never be autoclaved in sealed containers.
  • Liquids inside the containers should only be filled 2/3rd of the total volume to prevent spilling.
  • Plastic or polyethylene trays or containers should not be used to prevent melting
  • Never autoclave flammable, reactive, corrosive, toxic, or radioactive materials, household bleach, or paraffin-embedded tissue

What is the difference between automatic and manual autoclaves?

Automatic autoclaves are extremely easy to operate thus why they are generally more expensive than manual units. This is a set it and forget it type of experience. All you need to do is set the autoclave to on/start, and you’re ready to go. How does it all work? 

  1. The water will fill the chamber automatically after you select your specific sterilization settings, which will typically be indicated by a light for your convenience.
  2. After this time, the steam sterilization process will take place and sanitize your specific content.
  3. Once your sterilization settings have been configured to their optimal cleaning points, the autoclave will exhaust the steam and automatically start the drying cycle.
  4. Once the drying cycle is complete, your unit will alert you when the sterilization process is complete.
Example of women using an automatic autoclave
(Example of an Automatic Autoclave being unloaded)

Manual autoclaves require more work on your part. They are not as easy to operate as automatic units but they are much less expensive and easier to repair. They are also less expensive. How does this process differ from automatic units?

  1. Since this is a manual unit, you need to patiently wait for the water to flow into the unit and set the autoclave to the fill position each time.
  2. Once the water is filled, you need to load your items for sterilization and shut the autoclave's door.
  3. Once the door is shut, lock the autoclave with its manual lock, set your desired temperature and set its timer.
  4. Once the autoclave is done sterilizing, you will need to manually open the door and exhaust the steam before setting the dry cycle. Please take note that the pressure will need to drop to zero as well.
  5. Set the autoclave to its dry cycle by resetting its timer.
  6. Once the timer is up, usually by a beep or buzzing sound, the content can be removed.

As you can see, the manual process is much more tedious and time consuming. We always recommend our customers go with the automatic options, if they can afford it, but the manual process does the same job in its end. 

Example of manual autoclave from Tuttnauer
(Example of a manual autoclave with several functions)

As always, if you have any questions regarding autoclaves give us a call at 224-829-0325 or shoot us an email at info@leadsonics.com. Already made up your mind? Visit our autoclave shop for exclusive deals and discounts.  

Which autoclave should I choose? 

Choosing the right autoclave for you can be quite a challenge. We have created a comparison chart below to view all our models and how each one can be viewed specifically for your needs. 

Check out our comparison tables below:

Automatic & Digital Autoclaves
EZ10 EZ9  EZ9 Plus EZ11Plus EZ10k Elara11  T-Edge 3870EA
Chamber Dimensions 10" x 19" 9" x 18" 9" x 19.8" 11" x 19.8" 10" x 19" 11" x 19.8"  18" x 10" 15" x 30"
Overall Dimensions (D x W x H) 21.5" x 20" x 14.4"  21.5" x 20"  x 14.4"  24.8"  x 19.1" x 15.1" 24.8" x 20.9"  x 17.3" 21.5" x 20" x 14.4"   26"  x 20.9" x 17.3" 18.9" x 19.23" x 22.44" 34.5" x 26"  x 20.6"
Tray Dimensions (D x W x H) 16.3"  x 6.7"  x 0.8"  16.3" x 6.7" x 0.8"  16.3"  x 6.7" x 0.6" 16.3"  x 6.7"  x 0.6" 16.3"  x 6.7"  x 0.8"  16.3" x 6.7" x 0.6" 16.5" x 7.4" x 0.8" 26.6"  x 11.3"  x 1"
26.6"  x 13.8"  x 1"
Number of Trays 4 3 3 5 4 5 5 2
Chamber Volume 6 gallons 5 gallons 5.2 gallons 7.5 gallons 6 gallons 7.5 gallons 6 gallons 22 gallons
Cassette Capacity 3 full and 3 half 2 full and 2 half 2 full and 2 half 4 full and 4 half 3 full and 3 half 4 full and 4 half 3 full and 3 half 15 full
Unwrapped Cycle Time Cold: 30 min
Hot: 14 min
Cold: 27 min
Hot: 13 min
20 min 20 min Cold: 21 min
Hot: 11 min
20 min 20 - 60 min Cold: 32 min
Hot: 23 min
Voltage 120 V 120 V 120 V 120 V 230 V 230 V 230 V 230 V
Frequency 50/60 Hz 50/60 Hz 50/60 Hz 50/60 Hz 50/60 Hz 50/60 Hz 60 Hz 50/60 Hz
Power 1400 W 1400 W 1400 W 1400 W 2200 W 2300 W 2000 W 3000 W
Current 12 A 12 A 12 A 12 A 10 A 10 A 10 A 13.6 A
Weight 95 lb 95 lb 104 lb 126 lb 95 lb 171 lb 110 lb 278 lb
Type Automatic Automatic Automatic Automatic Automatic Automatic Auto/Digital Automatic
Warranty  2 Year 2 Year 2 Year 2 Year 2 Year 1 Year 2 Year 2 Year
Price $4,959.99 $4,499.99 $4,499.99 $5,075.99 $5,189.99 $8,849.99 $6,380.99 $15,399.00

 

Manual/Semi Autoclaves

Valueklave 1730 2340M 2540M 2540MK Kwiklave 2540MKA 3870M
Chamber Dimensions 7" x 13" 9" x 18" 10" x 19" 10" x 19" 10" x 19" 15" x 30"
Overall Dimensions (D x W x H) 17.9"  x 17.4" x 12" 21.5" x 20"  x 14.4"  21.5" x 20" x 14.4" 21.5" x 20" x 14.4" 21.5" x 20" x 14.4" 34.5" x 26"  x 20.6"
Tray Dimensions (D x W x H) 11.6"  x 4.7" x 0.8" 16.3" x 6.7" x 0.8"  16.3"  x 6.7" x 0.8" 16.3"  x 6.7" x 0.8" 16.3"  x 6.7" x 0.8" 26.6"  x 11.3"  x 1"
26.6"  x 13.8"  x 1"
Number of Trays 3 3 4 4 4 2
Chamber Volume 2 gallons 5 gallons 6 gallons 6 gallons 6 gallons 22 gallons
Cassette Capacity 2 half 2 full and 2 half 3 full and 3 half 3 full and 3 half 3 full and 3 half 15 full
Unwrapped Cycle Time Cold: 16 min
Hot: 11 min
Cold: 27 min
Hot: 13 min
Cold: 30 min
Hot: 14 min
Cold: 21 min
Hot: 11 min
Cold: 16 min
Hot: 12 min
Cold: 32 min
Hot: 23 mins
Voltage 120 V 120 V 120 V 230 V 230 V 230 V
Frequency 50/60 Hz 50/60 Hz 50/60 Hz 50/60 Hz 50/60 Hz 50/60 Hz
Power 1350 W 1400 W 1400 W 2200 W 2200 W 3000 W
Current 11 A 12 A 12 A 10 A 10 A 13.6 A
Weight 50 lb 85 lb 85 lb 85 lb 85 lb 278 lb
Type Manual Manual Manual Manual Semi Manual
Warranty  1 Year 1 Year 1 Year 1 Year 1 Year 2 Year
Price $2,511.99 $3,989.99 $4,539.99 $4,819.99 $5,319.99 $12,249.99

 

Go Back