If I were to ask what the most under-appreciated component of an autoclave (or any other steam based bulk sterilization device) was, what would you answer? Is it the heating element? The controller? Water pump? Safety valves? Amidst all these durable, expensive, and essential items, many autoclave technicians and service agents would struggle to find common consensus. However, the most overlooked and undervalued component in any autoclave is the simple piece of rubber that helps achieve a proper door seal amidst high pressures and temperatures – universally referred to as a door gasket. This unassuming item can make a world of difference in a sterilizer’s performance and operational readiness – making a door gasket’s routine maintenance and regularly scheduled replacement imperative.
A gasket that is worse for wear can slowly degrade an autoclave’s performance over time, until it is completely unable to maintain baseline pressures and temperatures deemed acceptable for sterile processing. How can these pitfalls be avoided, and furthermore, what evidence is there for an autoclave’s dependency on this underrated rubber ring? Hopefully, a brief overview of door gasket materials, design, function, and maintenance can help answer this important question.
A simple search engine query will show that there are a multitude of autoclave door gaskets available in today’s increasing web-based, medical device replacement parts market. Seemingly every major autoclave manufacturer and third-party aftermarket parts provider offers a catalog of gaskets with different material blends, various price points, specific dimensions, and model specific designs. Because of this variety, every sterile processing technician should understand what makes an autoclave door gasket different from door gaskets with different applications and uses in the medical field, such as the door gaskets found in sterile storage cabinets or biomedical ultra-low freezers. At their core, all door gaskets across all kinds of equipment serve the same purpose – maintaining a seal between the contents within the enclosed chamber and the outside world. No matter the device in question, this is an essential function in all sterile processing environments.
Due to its inherent properties of high tensile strength and resistance to friction, extreme temperatures, chemical compounds, and water swell, rubber materials of all variants are often used as the primary component in door gasket manufacturing. Neoprene, silicone, nitrile, ethylene propylene diene monomer (EPDM), butyl, fluorosilicone, and styrene-butadiene (SBR) rubbers are all commonly used in door gaskets across all industries and applications. Specific to the biomedical and sterile processing fields, silicone and neoprene (polychloroprene) based rubber compounds, and their subsidiary hybrids, are most often used.
Between these two rubber variants, silicone is by far the overwhelming choice for door gasket duties in autoclaves and steam sterilizers. Silicone rubber compounds have a wide range of tolerance, as it can withstand temperatures between -100℉ to 450℉. It is also more malleable, able to endure more pressure and compression, and more chemically inert and stable than other rubber compounds. All of these qualities make silicone the leading choice for use in autoclave door gaskets.
But if silicone is the clear choice, then why even mention neoprene? Neoprene-based rubber compounds are still used in door gaskets for other, non-autoclave pieces of equipment involved in the sterilization process – such as washers and sterile cabinets. There is far less of a requirement for extreme heat and pressure resistance in these devices as compared to autoclaves and steam sterilizers. The focus with door gaskets in these devices is more on the malleability and form-fitting side of the coin. Because of this, neoprene’s durability and cheaper price to produce compared to silicone make it an easy choice to use in cabinets and washers.
Now that you know which type of gasket material is best for when it comes to steam sterilization, how do you make sure the silicone maintains its inherent resistive properties for the longest amount of time? No matter what, every silicone gasket will expand and contract several millimeters throughout every cycle the autoclave runs. This is a sword that cuts both ways – on the positive side, this expansion helps to create a better seal against the autoclave chamber, allowing peak cycle temperatures and pressures. On the negative side, this constant fluctuation between expanding and contracting, heating and cooling, and tightening and loosening, will all incur inevitable wear and tear on the gasket.
Beyond the wear and tear incurred by the running of the autoclave itself, other environmental factors incur risks on a door gaskets lifespan. Water that is hard or poor in quality, chemical cleaners, and sterilely processed media that the gasket is exposed to all impact its survivability. If you are working with non-distilled, calcium rich, hard water (never recommended), it is suggested that you wipe down your gasket with a cloth, warm water, and a mild neutral detergent at least once a day, preferably after every cycle. Even in facilities with regular access to distilled water, it is still beneficial to wipe down the gasket once a day to avoid any sort of water droplets to cause particulate buildup on the gasket over time.
The gasket’s fit in the autoclave chamber or door groove is also an important consideration. If it is not emplaced or installed correctly, the application of pressure through the door locking mechanism can create uneven wear on the gasket as it is pressed onto the chamber frame. With this in mind, regularly check to see that there are no bumps or bunched up portions of the door gasket throughout the mounting channel – the entire gasket should fit tightly, but evenly, throughout the mount. To be extra sure of proper fit, you can always use precision calipers to measure the amount that the door gasket extrudes from the door itself at multiple points along the mounting groove to ensure consistent fit and even application of force by the locking mechanism. Inspecting the gasket along its entire exposed surface using a penlight or exam light will also help highlight cuts, tearing, micro-abrasions, bubbling and pitting not easily detectable with the naked eye alone.
While an ounce of maintenance yields a pound of cure, there is only so much you can do to keep that vulcanized silicone band in tip-top shape. So how does one know that their gasket needs replacing? There are a multitude of warning signs most autoclaves will exhibit in this regard, either through controller alarm messages or performance issues. One fairly obvious sign that an autoclave’s gasket is worse for wear is water dripping, pooling, or leaking from the door even when it is tightly closed. If you are certain the door is closed firmly, the gasket is fitted correctly, and the water leak is coming from behind the door and within the chamber, there is a good chance that the gasket is compromised and in need of replacement. Another tell-tale sign of a damaged gasket is a low pressure alarm from the autoclave’s controller. If the water level electrode is clean, the gasket is fitted, and you are sure that the door is closed tightly, your gasket’s failing structural integrity is most likely the culprit. A low water message can be another notification to look out for regarding gasket health. If you have already cleaned the water level electrode and confirmed that the door is closed tightly, start reaching for your replacement gasket.
If you are not having problems with your gasket, but feel like you haven’t replaced it in a while, what should the criteria for replacement be? Some might argue that if it isn’t broke, don’t fix it. Others use overall cycle counts between replacement as a rule of thumb. If you are running your autoclave more than two or three times a day (or more than 600 cycles annually), most manufacturers recommend replacing the gasket twice a year or more. For sterilizers being run around 300 times a year, a new gasket might last a full year or more.
Whether you have your own biomedical engineering and repair department, hire a third-party service provider, or do it yourself, maintaining and replacing your gaskets is imperative for your unit’s operational rate. Your gasket is far too easy to maintain and replace to let it get in the way of your efficiency. Hopefully, this article shed some light in helping you make the right decisions regarding door gasket selection, maintenance, and replacement.
(This special release content was written by Robert Wolfe, Marketing and Business Development Intern at Minnesota Medical Specialists & Refrigeration. For more information and education on this topic, you can contact their team at: service@minnesotamedical.com )