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Gravity Cycle vs. Vacuum Cycle: When to Use a Vacuum Cycle

A standard autoclave cycle is a gravity cycle—so-called because, as steam rises to fill the sterilizer chamber, it displaces the cold air already in the chamber, which is then drawn out of the vessel by gravity. Under many circumstances, this process works just fine—and its simplicity ensures relatively minimal parts, electricity use, and cost. 

However, sometimes a gravity cycle will be suboptimal; in those instances, a vacuum cycle works better. A vacuum cycle doesn’t wait for gravity to do the work. Instead it forces cold pockets out of the chamber and ensures even steam contact throughout the load. Adding just one pre-cycle vacuum pulse improves sterilization by about 90%; using three pre-cycle vacuum pulses virtually guarantees successful sterilization. 

A “pre-vac” vacuum cycle can make a significant difference under many circumstances. But there are several key situations when you’re sure to benefit.

Five Times to Run a Vacuum Instead of Gravity Cycle

  1. Porous loads are a challenge to fully permeate with steam without a vacuum cycle, leaving cold pockets that don’t get sterilized. 
  2. Erlenmeyer flasks, tubing, and other narrow-mouthed containers can trap cold air and sometimes prevent complete sterilization. An autoclave that allows for “pre-vac” cycles can help with this. An autoclave with a vacuum pump allows you to draw a partial vacuum in the chamber during the initial heating period when the chamber fills with steam. “Pulsing” this vacuum entirely removes pockets of cold air from the chamber that might otherwise linger. The vacuum improves reliability of sterilizing every load, every time.
  3. Because vacuum cycles speed heating and improve consistency throughout the chamber, they can be helpful when it’s important to run a non-liquid load as quickly as possible. Rather than wait passively for gravity to pull cold air out, the vacuum cycle speeds the process by actively pumping cold air out of the chamber. 
  4. A vacuum pump also permits for a “post-cycle vacuum” stage, which enables your load to finish dryer (even when faced with unfortunate—though all too common—lab practices, like foiling beakers).
  5. Vacuum cycles benefit waste loads as well, ensuring that plastic especially—which might otherwise trap cold air, preventing complete sterilization—heats consistently and thoroughly enough to complete decontamination prior to disposal.

Have you been relying on gravity to do a vacuum’s job? Priorclave builds your autoclave to order, so we build it according to your lab’s unique requirements and demands. Get in touch with us to discuss what combination of features will serve you best.