First-time autoclave shoppers can easily be overwhelmed by all the technical jargon they have to decipher and consider before purchasing a steam sterilizer. One of the most common points of confusion is how to determine which autoclave cycles are most appropriate for different applications.

In general, there are three main types of steam sterilization cycles: gravity, vacuum, and liquid. All three use high temperature and high pressure for disinfection; however, each cycle uses a slightly different custom process to maximize disinfection conditions for certain items.

Gravity cycle

Gravity is the simplest and most common autoclave cycle. As the name suggests, the cycle relies on gravity to replace air with steam. When steam is pumped into the chamber, it rises to the top because it is less dense than air. This in turn forces the air to the bottom of the chamber, where it is completely expelled from the chamber through a vent. After the cycle is complete, the steam is released through the vent and cooled. This mechanism contributes to the simplicity of its design and does not rely on peripheral mechanisms to replace ambient air with steam. Making these types of autoclaves more affordable and reliable.

The cycle is well suited to sterilize the most common laboratory media, biohazardous waste, glassware, and certain unpackaged items.

Vacuum cycle

Autoclaves designed for vacuum Cycle will be equipped with a vacuum system. The system begins each cycle with alternating steam jets and vacuum suction, which work together to completely remove air from the chamber. The vacuum feature in these autoclaves allows for deeper disinfection of contents because it completely empties ambient air from them, allows high-temperature vapors to penetrate and disinfect areas normally occupied by ambient air, and can more effectively disinfect hard-to-reach areas within certain items.

Because of the vacuum, this cycle is ideal for bagged or wrapped loads, porous materials, and packaging, such as pipettes or surgical instruments.

Liquid cycle

For liquid cycle, it is not necessary to remove air from the chamber to ensure successful sterilization, but the actual sterilization is achieved by the liquid sterilizing itself due to its increased temperature. Therefore, there is no need to remove indoor air.

Moreover, due to the delicate nature of rapidly heating and cooling liquids, special precautions must be taken to avoid boiling them in the autoclave. The boiling effect is known to be problematic because it causes liquid loss and can cause chaos inside the autoclave. Apparently, no researcher likes to clean up spilled hot liquids or exploding glassware at the end of a liquid cycle, which is both unpleasant and potentially dangerous. To help combat the risk of boiling, chamber pressure must be released slowly. For this reason, the cycle is sometimes referred to as the “slow exhaust” method. By slowing the release of pressure, the temperature of the liquid will slowly cool as the pressure decreases.