In critical applications such as medical device sterilization, laboratory sterilization, and aseptic production in food and pharmaceutical manufacturing, autoclaves remain the core equipment for maintaining absolute sterility. It can completely eliminate bacteria, fungi and other microorganisms, establishing a robust defense for safe operations across various industries. This page will introduce the composition and actual operation of the autoclave, helping you clearly understand its working logic and better adapt to your needs.
What is an Autoclave?
An autoclave is a core equipment that uses high-temperature and high-pressure saturated steam to kill microorganisms. It is primarily used for the thorough sterilization of items that withstand high temperatures and humidity. It is a key tool for maintaining a sterile environment in fields such as medicine, research, food processing, and pharmaceutical instruments.
It achieves this by combining specific temperature, pressure, and time. It damages the protein, nucleic acid, and cell membrane structures of microorganisms. For example, it can completely kill bacteria spores, fungal spores, and other highly resilient microorganisms. There are no live microorganisms remaining in the sterilized items.
Critical Components of an Autoclave
Sterilization Chamber
The sterilization chamber is a sealed space that holds items awaiting sterilization and generates high-pressure steam. As the core vessel of the equipment, its design directly impacts sterilization efficiency and safety.
It is typically constructed from 304 or 316 stainless steel. This material offers corrosion resistance, high-temperature tolerance, and high strength for demanding applications. It can withstand temperatures exceeding 134°C and pressures above 200 kPa , preventing rust or deformation during prolonged use.
Its shape is predominantly cylindrical, as this structure evenly distributes pressure, avoiding localized stress concentrations that could cause rupture.
Steam Generation System
The function of a steam generation system is to heat water to boiling point, producing saturated steam. It is primarily divided into two types: built-in heating and external steam.
Built-in heating systems feature stainless steel electric heating elements immersed in deionized or distilled water. When energized, they heat the water to boiling to generate steam, making them suitable for small to medium-sized equipment.
External steam systems connect to an external centralized steam supply, making them ideal for large-scale equipment such as hospitals and factories.
Exhaust and Vacuum System
Cold air can hinder the thermal penetration of steam because cold air is dense and gathers at the bottom of the chamber, forming a cold zone, causing local temperatures to be lower than the set value. Therefore, cold air must be completely removed through the exhaust or vacuum system.
Exhaust System
Lower exhaust valve: Located at the bottom of the chamber. It is opened at the beginning of sterilization to allow steam carrying cold air to be expelled from the bottom until pure steam is expelled from the exhaust port.
Upper exhaust valve: Some equipment has an upper exhaust valve on the top, which assists in expelling a small amount of cold air from the upper part of the chamber.
Vacuum System
Vacuum pump: Through a cycle of vacuuming – injecting steam, the cold air in the chamber is completely removed. This is particularly suitable for items that are difficult to penetrate, such as surgical instrument packages and rubber products, avoiding the formation of a cold zone and achieving higher sterilization efficiency.
How Does an Autoclave Work?
The core principle of an autoclave is to utilize the thermal penetrability and latent heat release of saturated steam to achieve efficient microbial sterilization. Below is an example of the complete working process of a vented autoclave, demonstrating how an autoclave operates.
Step 1: Preparation Stage
Check the water level in the built-in water tank, the door sealing ring, safety devices, and drainage outlets. The sterilized items must meet the requirements of being resistant to high temperatures and humidity. Solid items should be wrapped in breathable materials, and liquid items should be placed in containers with exhaust holes. You can set disinfection parameters based on the characteristics of the items, including temperature, pressure, and duration.
Step 2 : Exhausting stage
Thoroughly purging cold air from the sterilization chamber is essential for successful sterilization. If cold air accumulates at the chamber bottom, it creates cold spots that cause localized sterilization failure. Therefore, complete exhaustion is mandatory during this phase.
First, start the equipment. The built-in heating element powers on to heat the water in the tank, boiling it to produce saturated steam. Then open the lower exhaust valve, allowing steam to carry the cold air out through the exhaust port.
When the steam exiting the exhaust port forms a white column without any white mist, or when the equipment’s temperature sensor indicates a temperature above 100°C, this indicates exhausting is complete. The exhaust valve can then be closed.
Step 3: Boosting Stage
After the venting process is complete, the temperature and pressure inside the container must rise to the set values. This stage relies on the coordinated operation of the pressure and temperature control systems.
Following the closure of the vent valve, steam continues to accumulate within the sealed chamber, causing the pressure to gradually increase. Since the boiling point of water is proportional to pressure, both temperature and pressure rise synchronously.
The pressurization phase concludes when both temperature and pressure stabilize at the set values.
During this phase, you must ensure a steady pressurization rate. Rapid pressurization may cause uneven steam distribution within the chamber or lead to glassware rupture due to excessive internal-external pressure differentials. If temperature and pressure fail to align during pressurization, residual cold air remains—requiring a repeat venting cycle.
Step 4: Sterilization Stage
Once the temperature and pressure reach the set values, the sterilization stage begins. The latent heat of saturated steam rapidly penetrates the interior of the items, causing both the inside and outside temperatures of the items to reach the set temperature. To kill common bacteria, such as Escherichia coli, it takes 1-2 minutes, while to kill resistant bacterial spores, such as Clostridium tetani, it takes 15-20 minutes.
The humidity of the steam can soften the cell walls of microorganisms, enhancing the heat penetration effect. Compared to dry heat sterilization, such as in an oven, its efficiency is 10-30 times higher.
Step 5: Pressure Reduction Phase
After sterilization is complete, turn off the heating element and slowly open the lower exhaust valve. Adjust it to a small opening using the valve knob. During this phase, carefully control the rate of pressure reduction to gradually lower the chamber pressure and vent steam, preventing damage to items caused by sudden pressure drops.
For liquid items, pressure reduction must be even slower. If pressure drops too rapidly, the internal vapor pressure of the liquid can momentarily exceed external atmospheric pressure, causing violent boiling and liquid to surge out of the container.
For pulsed vacuum equipment, a vacuum pump can be used to extract steam, allowing faster pressure reduction, though control remains essential.
The pressure reduction phase concludes only when the chamber pressure drops to atmospheric pressure and the temperature falls below 100°C.
Step 6: Drying and Removal
After pressure reduction, determine whether drying is necessary based on the characteristics of the items. Items requiring no drying proceed directly to the cooling phase. During cooling, open the sterilization door and maintain a 5-10mm gap to allow residual heat and steam to dissipate naturally. This prevents rapid influx of cold air, which could cause glassware to shatter due to extreme temperature differentials. Wait until the chamber temperature reaches room temperature before turning off the equipment power.
When removing items, avoid touching the chamber walls to prevent burns. Sterilized items must be immediately placed in a sterile environment such as a laminar flow hood or sterile storage cabinet to prevent secondary contamination and ensure safe subsequent use.
Conclusion
You can gain a thorough understanding of how autoclaves work from the introduction on this page. Every step of its operation revolves around the core principles of efficient sterilization and safety protection, ensuring the equipment meets the demands of diverse scenarios including medical, research, food, and pharmaceutical applications. It is an essential tool for achieving high-level sterility. If you require further guidance on equipment selection or have customized needs, please feel free to contact us. Let our professional equipment fortify the defenses for your sterile production and experimental safety.
