The autoclave’s working principle relies on hot steam, which circulates inside a high-pressure chamber where the items needing disinfection are placed. As the steam interacts with the objects, the heat thoroughly eliminates the microbes, sterilizing all the items.

To learn more about the autoclave’s working principle, we’ve asked our experts for a detailed guide on the machine’s components, applications, types, and benefits.

Read on for more information on the autoclave’s working principle and uses.

What Is an Autoclave?

An autoclave is a machine that uses high-pressure steam for the sterilization of lab equipment, surgical tools, and biomedical waste in laboratories and medical settings.

Also known as the steam sterilizer, the autoclave effectively eliminates viruses, bacteria, fungi, spores, and other microbes that could be potentially dangerous.

Aside from its applications in research and medical fields, high-pressure sterilization can also be used for industrial purposes. Many industries, including construction, materials science, and aerospace manufacturing, rely on autoclaves for disinfecting, performing quality checks, and other purposes.

What Is the Autoclave Working Principle?

The autoclave working principle is based on generating high-pressure steam that can eradicate bacteria, viruses, fungi, and other pathogens. When exposed to it for a set period of time, lab equipment or surgical tools become sterilized and ready for further use.

Below, we will explore the basic principle of the autoclave in more detail.

Steam Generation

Steam is at the core of an autoclave’s working principle, as it is a convenient medium for transferring heat and penetrating the equipment’s hard-to-reach nooks and crannies. So, at the beginning of a sterilization cycle, steam generators vaporize water and release the steam into the pressure chamber where items that need to be sterilized are placed.

It’s worth mentioning that not all steam is suitable for sterilization. Typically, sterilizers use steam composed of 97% vapor and 3% moisture, as this kind is the most effective at heat transfer. If there’s less than 3% moisture, the steam is considered superheated or dry, and it’s not useful for sterilization.

Purge Phase

Once the steam released from the steam generator begins flowing through the sterilizer, the autoclave’s pressure and temperature begin increasing. At this point, air must be removed from the device—its presence, even in small pockets, enables the growth of pathogens and inhibits sterilization.

In most autoclaves, the working principle is to let the incoming steam replace the air and use gravity to push it out through a drain. However, some employ a more active approach, utilizing vacuum pumps to remove the air quickly and thoroughly.

Sterilization Phase

During the sterilization (exposure) phase, the autoclave’s control system closes the exhaust valve, creating an entirely sealed chamber. Then, temperature and pressure rise until they reach preset values—usually 250°F (121°C) and 103 kPa.

Under these conditions, the steam sterilization process begins—the high temperature breaks down the proteins in the microbes’ cell walls and kills them. The autoclave maintains the same temperature and pressure throughout the entire cycle, which typically lasts 15–20 minutes, though this, too, is subject to change.

Exhaust and Cooling

When the autoclave sterilization cycle is completed, the exhaust valve opens, allowing the chamber to depressurize.At this stage, the components are still very hot, so it is not advisable to touch them without heat-resistant gloves.

4 Key Components of Autoclaves

The key components of autoclaves include a pressure chamber, a door or lid, a safety valve, a steam generator, and sometimes a vacuum generator. Despite their complex design, autoclaves are easy to operate and largely automatic, making them ideal for laboratory and clinical settings.

That said, let’s examine crucial parts of an autoclave in more detail.

#1. Pressure Chamber

The pressure chamber is the main body of the autoclave, where items to be sterilized are placed and processed. Typically, pressure chambers are made of stainless steel to withstand high temperatures, pressure, and corrosive environments.

Some autoclaves are equipped with a cast iron jacket surrounding the pressure chamber. This jacket is constantly flooded with steam, which can instantly be used for sterilization. That way, waiting for steam generation is reduced, and sterilization can be completed far quicker.

#2. Door

The door separates the inside of the autoclave from the outside atmosphere, allowing the buildup of pressure and temperature in the chamber. It contains three parts: a pressure gauge, a whistle (not present in all autoclaves), and a safety lock.

However, it’s worth noting that all three components contribute to the autoclave’s safety. The pressure gauge shows the pressure buildup inside the chamber, alerting the staff in case of an issue. The whistle, on the other hand, controls the pressure by releasing small amounts of steam when necessary, similar to that of a pressure cooker.

#3. Safety Valve

The safety valve is the crucial part of the autoclave chamber, preventing excessive pressure buildup that could lead to an explosion when the machine isn’t working correctly. In such a case, the valve opens and releases the pressure, thus avoiding damage to the device and potential harm to the staff.

#4. Steam and Vacuum Generators

Steam and vacuum generators are at the core of an autoclave’s working principle, as the former generates the steam necessary for sterilization, while the latter removes air pockets from the pressure chamber. This guarantees that all pathogens can be thoroughly removed and that there are no conditions for their regrowth within the chamber.

4 Main Types of Autoclaves

Four types of autoclaves include gravity displacement, laboratory bench, S-type, and B-type autoclaves. All these perform the same function but differ in size and air removal methods.

Let’s explore these four common types of autoclaves in more detail.

#1. Gravity Displacement Autoclaves

Gravity displacement autoclaves, also known as the N-type, are the most common, with numerous applications in research labs and medical settings. Part of the reason they are so widespread is their cost—they are far more affordable than other, more sophisticated systems.

As their name implies, these machines use gravity for air displacement. Hot steam rises to the top of the chamber due to its lower density and gradually pushes air down into a drain vent. After some time, no air remains in the pressure chamber—only steam.

Gravity displacement autoclaves are primarily used for items with hard surfaces and shouldn’t be applied to equipment with small holes where air can get stuck, like syringes. Also, they are slower than more advanced types because they don’t use vacuum pumps for quick and thorough air removal.

#2. Laboratory Bench Autoclaves

Laboratory bench autoclaves are small sterilizers used for routine sterilizations in microbiological and clinical labs. They resemble pressure cookers and are ideal for laboratories that want to save space or can’t afford one of the larger, more complex machines.

#3. S-Type Autoclaves

S-type autoclaves are somewhat difficult to describe because their features can differ significantly from one model to another. Generally speaking, they are equipped with additional customization options compared to gravity displacement autoclaves, but they don’t always have vacuum pumps or drying mechanisms.

As a result, they also rely on gravity for air removal and thus aren’t suitable for all equipment and surgical tools. However, it’s advisable to read the manufacturer’s instructions for specifics, as some have greater capabilities than others.

#4. B-Type Autoclaves

Finally, B-type autoclaves are the most effective at sterilization but also the most expensive, making them inaccessible to labs with tighter budgets. These autoclaves use the so-called pre-vacuum sterilization with vacuum pumps that quickly remove air and allow steam to permeate the entire pressure chamber.

Consequently, they are much faster and more thorough than any other type, so they can be used for all kinds of tools—even hollow and intricate ones.

3 Critical Applications of Autoclaves

Autoclaves have applications in laboratories, medical fields, and industrial settings—essentially any field where sterilization is required. To accommodate the requirements of different disciplines and industries, autoclaves come in many shapes and sizes.

Let’s explore the common applications of autoclaves in more detail.

#1. Laboratories

Autoclaves are used to sterilize lab equipment, be it glassware, stainless steel instruments, or even gloves and similar lab safety equipment. Thanks to their unique working principle, autoclaves are crucial in microbiology, where they are applied to process biological waste before disposal and prepare culture media.

Autoclaves used in laboratories are typically small- to medium-sized, depending on the specific capacities and needs of the lab in question. Chemistry labs, for instance, are more likely to use bench autoclaves, as their sterilizing needs aren’t as great. On the other hand, biological and microbiological labs usually rely on large sterilizers.

#2. Medical Fields

The autoclave’s applications in healthcare include sterilizing surgical instruments, syringes, reusable protective gear, and other objects. Though many medical instruments are single-use today, steam sterilizers still have their place in many hospitals and clinics.

That’s partly because even some single-use items must be sterilized before disposal, especially if they are covered in blood or saliva. Bodily fluids typically carry pathogens that may be infectious, so they must be handled with care like other biological waste.

Like research labs, medical fields can use a range of autoclaves, usually settling on mid-sized ones. However, clinical laboratories are more likely to use B-type autoclaves, as they are the best sterilizers, particularly for complicated tools.

#3. Industrial Use

Autoclaves are a widespread method of industrial sterilization, although their applications go beyond that in many industries. For instance, porous concrete and laminated safety glass used in construction are made with the help of an autoclave, as are many different aircraft components.

Furthermore, autoclaves are used in many industries to artificially age materials to test their quality and resilience. This allows manufacturers to predict how their products will behave over time and whether they will retain their integrity. As a result, they can make adjustments to prolong their lifespans if necessary.

Industrial autoclaves are typically extremely large, with capacities of several thousand liters—ideal for holding aircraft parts or construction materials.

Advantages of Using Autoclaves

The advantages of using autoclaves are numerous and encompass the machine’s speed, convenience, and ease of use, among others. For these reasons, most experts choose autoclaves as ideal sterilizing options.

Here are three additional benefits of relying on an autoclave’s working principle:

• Effectiveness. Autoclaves are highly effective at eliminating microorganisms, thanks to the high-pressure steam applied in a heated chamber. This steam can easily reach all parts of the contaminated object, killing microbes with sustained heat. The whole process lasts less than half an hour, yet its effects are undeniable.
• Minimal effect on the environment. Since they don’t use detergents or chemicals that could harm the environment, autoclaves are considered eco-friendly sterilizers. They rely only on steam, which is vaporized water and, therefore, completely safe and non-toxic.
• Cost-effectiveness. Although autoclaves are by no means cheap, they last long and are used repeatedly, which makes them worth their price. A standard autoclave has a lifespan of ten years, but good maintenance, regular calibration, and adherence to the manufacturer’s instructions can increase it significantly.

What to Consider When Choosing an Autoclave

When choosing an autoclave, you should consider your needs, room capacity, and resources, as well as the machine’s specifics. It’s important not to rush into the process—take your time, do thorough research, and compare available options until you settle on the right one.

Here are some factors to take into account when purchasing an autoclave:

• Size. Autoclaves come in various sizes—some are as small as a pressure cooker, while others are large industrial machines with a capacity exceeding 1,000 liters. Still others, like vertical autoclaves, are specifically designed to save space despite being larger than average tabletop models. Ultimately, your choice of size will depend on your needs and lab capacity.
• Ease of use. Your new autoclave should have a simple interface where you can set the temperature and cycle duration. Its design should be intuitive, allowing even beginners to navigate it without extensive training.
• Type. As we’ve seen, there are four basic types of autoclaves with different features, benefits, and disadvantages. Consider which one matches your needs and budget, but make sure to also look into specific models, especially when buying an S-type machine.
• Cost. A limited budget narrows the selection, making advanced types of autoclaves inaccessible. However, that may not be the case if you opt for a used lab equipment vendor, where you can find high-end steam sterilizers at competitive prices.

Used vs. New Autoclave

When it comes to pre-owned lab equipment, many lab owners tend to be skeptical, believing that its quality can’t compare to that of new instruments. They are particularly wary of potential deficiencies, which can impact the equipment’s performance and research results.

However, buying second-hand lab equipment from a trusted source, like Surplus Solutions, is proven to be safe, as all instruments must undergo rigorous quality checks. As a result, our equipment, including used autoclaves, is reliable, precise, and conforms to manufacturer’s specifications

Furthermore, these high-quality instruments are available at a fraction of the price of a new one, allowing you to put your funds into research instead of equipment.

Safety and Precaution Tips for Autoclaves

Safety and precaution tips for autoclaves include advice on how to use these machines effectively and avoid potential issues, damage, or injury. After all, autoclaves operate with high pressure and temperature, so misuse can have devastating consequences.

Here are some tips on handling autoclaves safely:

• Don’t place the autoclave on an unstable surface.
• Don’t overcrowd the equipment inside the pressure chamber; make several batches if there are many instruments to sterilize.
• Don’t seal containers inside the autoclave, as they pose an explosion risk.
• Don’t put flammable, toxic, corrosive, or radioactive materials inside the autoclave.
• Tightly close the door to ensure proper sterilization.
• Never attempt to open the autoclave while it’s working.
• Don’t block or cover the machine’s door.
• Immediately turn off the power if you notice strange smells or sounds.
• Wait for the pressure inside the device to reach zero before opening the door.
• Wear protective gear, such as heat-resistant gloves and eye protection, when unloading the autoclave.

Key Takeaways

While exploring the autoclave’s working principle, we’ve learned more about its components, types, and applications, including those beyond the basic sterilizing one. An essential piece of lab equipment in microbiological and clinical labs, the autoclave is practical, environmentally friendly, and easy to use.

So, if you are looking for an affordable steam sterilizer, Surplus Solutions has quite an impressive selection. Aside from autoclaves, we offer other types of used lab equipment that meet all manufacturer’s specifications. Make sure to visit our website often and keep an eye out for our new arrivals!

Autoclave Working Principle FAQ