Practice Tips #105: Breathe In, Breathe Out – The Secret of the Sterilizer Bellows

The sterilizer helps you maintain proper infection control, making it one of the most important pieces of equipment in the dental office. Without a sterilizer, you can’t have sterile instruments and you can’t perform dentistry. Keeping your sterilizer running is integral to keeping your office running. So what is the secret of the sterilizer bellows?

In previous issues of Practice Tips we’ve discussed basic function and troubleshooting common to all sterilizers and sterilizer routine maintenance. In each of these issues, we’ve mentioned the sterilizer bellows, a component used in all autoclaves.

Sterilizer Function

In order to render instruments sterile, an autoclave needs to subject them to super-heated steam under pressure at a specified temperature for a given time. Most autoclaves deliver optimum performance at 135° C at 214 kpa i.e. 275° F. They also need to maintaine a 30 psi for just a few minutes.

At the beginning of the cycle, water enters the chamber of the autoclave (containing the dirty instruments). The chamber heats up, converting the water to steam, saturating the instruments. The steam is under pressure, so the fine grooves and recessed areas of the surface, and internal passages of the instruments, come in contact with the heated steam.

In order for the chamber to pressurize, it needs to breathe. As your autoclave heats up and the water begins to boil, the air in the chamber needs to vent, so it can be displaced by steam. This allows nothing but steam to fill the chamber of your autoclave. The bellows opens and closes throughout the cycle, in response to the changing chamber conditions. This allows air from the chamber to exhaust and be displaced by the steam. This allows the inlet of fresh air as the chamber cools and the steam to condense.

Malfunctioning Bellows

A malfunctioning bellows affects full sterilization pressure and thus temperature. There is a linear progression between the two conditions — leading to an under pressure condition. A failing bellows can also prevent fresh air in as the autoclave attempts to cool, which leads to an over-pressure and over-temperature condition.

Staying aware of the relationship between temperature and pressure helps with troubleshooting a failing sterilizer. The following table is a handy reference of this progression between the two:

Graphic Showing Pressure and Temperature

NOTE: Print this table and keep it near your sterilizer as a reference.

Bellows Types

A few common designs of the bellows are pictured below. Compare the photos to what is in your sterilizer to familiarize yourself with your sterilizer’s components.

images of sterilizer bellows

PHOTO: Pelton & Crane Bellows Kit (#PA-32), Tuttnauer Door Bellows (#TU-19), Midmark Air Vent Bellows (#MR-89)

The bellows is one of the key components to allow pressurization of the chamber. It should be one of the first things to look at, should you have a pressure-related issue, (along with the door gasket).

As the bellows opens and closes throughout the cycle, it can be prone to wear and should be replaced annually as part of your routine sterilizer maintenance. This is why the appropriate bellows is included with each of our sterilizer preventive maintenance kits.

No longer a secret - with routine maintenance of the bellows, both you and your sterilizer can breathe easy knowing that your instruments are sterile.


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