Not all autoclaves include vacuum features, because not every lab needs them. There’s no value in having a feature you never use, which still might break and force your entire autoclave offline.

There are three scenarios where vacuum features are a must-have, and few others where they’d be nice to have. Which are part of the day-to-day work of your lab?

Vacuum vs. Gravity Cycles: What’s the Difference?

There are two types of autoclave cycles: vacuum and gravity.

A “standard” autoclave cycle is a gravity cycle. Steam rises to fill the sterilizer chamber, displacing the cold air already in the chamber. The cold air gets drawn out of the vessel by gravity. This is nice because of its simplicity. There are no extra pumps or parts (seals, actuators, controllers) that could go bad. As anyone who has maintained a lab knows, simpler tends to mean more durable, with fewer things that could go wrong. But that simplicity comes at a price: cycles may be slower and less thorough. Cold air can get trapped and compromise the effectiveness of the sterilization process.

The alternative is a vacuum cycle. Here a vacuum pump forcefully draws out the cold air and saturates the chamber with steam. Cold pockets are forced out of the chamber, and steam makes direct contact with the entire load.

Is a Vacuum Autoclave a “Must-have” for Me?

Your choice depends upon how you’re planning to use your autoclave—and how you think it’s actually most likely to be used over the course of the many years your lab owns it.

When Vacuum Features Are a Must-Have

You’ll need vacuum features if you regularly deal with three main load types: narrow containers, dense/porous loads, and high-security biocontainment.

1. Some load types are like mazes. The materials themselves—glass, plastic, etc.—are easy for steam to sterilize, but the load creates a labyrinth that it’s hard for steam to navigate. Erlenmeyer flasks, tubing, reusable pipette tips, and other containers with narrow bodies and openings create these sorts of dead-end mazes where steam struggles to flow to every nook and cranny. An autoclave with a vacuum pump can 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.
2. Wrapped instruments, soil, and textiles are among the more common dense/porous loads sterilized in labs. These loads are materials or packages that are in and of themselves challenging to fully permeate with steam. Each pulse of the vacuum drives that steam deeper into the load, much as squeezing a submerged sponge brings more water deeper into the mass.
3. For high-security biocontainment, it’s always better to be safe than sorry. A vacuum cycle ensures even steam contact throughout each load. Adding just a single pre-cycle vacuum pulse improves sterilization by about 90%; using three pre-cycle vacuum pulses virtually guarantees successful sterilization.

Times When Vacuum Features are Not Essential, but Still Help

There are other items when the vacuum isn’t critical, but certainly helps. These include when autoclaving liquid loads and when you want a dryer finish.

1. 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 of the chamber, a vacuum cycle speeds the process of flooding the chamber with steam by actively pumping cold air out of the chamber.
2. A vacuum pump also permits for a “post-cycle vacuum” stage, which speeds evaporation for a dryer final load (even when faced with unfortunate—though all too common—lab practices, like foil-wrapped beakers).

Still not sure whether an autoclave with vacuum features is what you want—or what you need? Let’s chat about how you plan to use your autoclave, how long you’ll have it, and what might change along the way. We’ve got options—let’s talk about the right ones for your lab.