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Practice Tips #93: Sterilizer Door Gaskets (The Seal of Sterility)

The steam (autoclave) and chemical vapor (chemiclave) sterilizer are the workhorses of the dental office and all sterilizers use a "seal" or "door gasket" of some sort.  In this month's Practice Tip, we’re going to look a little further into  door gaskets— how they work and why they wear out as frequently as they do.

In an earlier post (Practice Tip #14), we gave you a routine maintenance checklist for your sterilizer. One component of that list consists of checking and maintaining the door gaskets, as well as how often to change these simple, but important components.

Almost all sterilizer door gaskets are manufactured from fluorosilicone. This material is great because it has oil and fluid resistance and is tolerant of high temperatures with a melting point in excess of 400° F. It is soft enough to seal well, but resilient enough to withstand the punishment of repetitive cycles.

While fluorosilicone has a high melting point, it will constrict (shrink) at about 200° F. Most sterilizer cycles run at 250° F - 275° F, so, well above this point. This means that every time you run your sterilizer, your door gasket will shrink slightly. To allow for this shrinkage, door gaskets are purposely made slightly larger than the surface area they are sealing. They are designed to “shrink to fit” (just like your Levi’s). Unlike blue jeans, your door gasket will expand after the cycle is complete and it returns to room temperature. This means that every time your sterilizer is used, the door gasket will stretch and then shrink. Considering that, it’s pretty amazing they hold their shape and integrity for hundreds of cycles or more.

As gaskets contract and expand hundreds of times, they will typically end their usefulness smaller than when they were first installed. This is one of the reasons you need to be careful about comparing a new, fresh gasket, to an old, worn-out one to gauge specifications. More often than not, a worn gasket will be undersized and often will get pinched in the door, causing large pieces to come off of the gasket.

Since it’s expected for a new gasket to be oversized, how will it fit your sterilizer?

You need to plan for the contraction of the gasket when you install it. It’s important that the gasket be allowed to shrink evenly throughout its circumference, so that it will seal when the temperature of a cycle is achieved.

When installing a door gasket, seat the gasket at the “corners” first. This allows the excess to be evenly spaced around the circumference, leaving you with several very small gaps. These small gaps will all be closed as the gasket shrinks once the cycle is begun. If you seat one section of the gasket at a time and then run your finger around the circumference to seat the remainder, you will be left with one large gap in a corner. The resulting gap will be far too large for the inevitable shrinkage to correct. This is not what you want.

Gasket Fitting

As you can see above, it is normal to have gaps around the circumference after installing a new gasket. The small gaps will correct once the sterilization cycle begins and the gasket shrinks. Having many small gaps is much better than only one or two very large gaps.

You can download our door gasket instructions to remind your staff on how to install them, every gasket we sell comes with them. A more detailed version is also shown below:

Gasket Instructions

By following the above instructions, you can be assured of a proper fit and will maximize the longevity of your gasket.

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