Seals don’t get much attention. They probably never will. But that doesn’t diminish just how essential they are to the background of everyday industrial life.
Though few even realize it, seals, gaskets, and o-rings are embedded in so many of the vital machines, equipment, and products that we all use every day. Without them, so many things would be much harder — if not impossible — to accomplish.
They aren’t all created equal, however. Different seals are tailor-made for different purposes, and it is important to understand the distinctions and unique properties of each type if you want to use the best ones. It doesn't just come down to cost or supplier. The materials themselves can break down over time — or fail instantly — if they are being asked to do a job that they aren't cut out for. How do you know which seals to pick? As always, you need to consult with expert engineers and designers who understand all the ins and outs of these nuanced factors. But the following specifications and applications are among the first that you will need to consider when trying to determine the best seal to use for any application.
If you need a seal that will be used solely in a moderate environment and will not be subjected to extreme temperatures, there is a broad range of materials that would be suitable. But some materials will degrade if they get too hot or too cold — especially after ongoing exposure.
This is one reason that silicone, one of the most versatile substances that can be used in a seal, has become so widespread and appreciated. As a rule, seals and o-rings made of this wonder substance are generally no worse for the wear even when facing highs above 400 degrees Fahrenheit and lows perhaps down even as far as -100 degrees.
By contrast, some other materials, as measured by standards from ASTM International, like ASTM D2137 and ASTM D1053, may become too brittle or stiff once they enter a low-temperature climate. In short, some elastomers bounce back as strong as ever while others break down and no longer retain their sealing properties afterward (or after repeated exposure).
As with the factors that govern temperature resistance, some seals simply aren’t up to the task of high-pressure situations. How we measure these factors can depend upon the application and the body you are referencing. The Norwegian Petroleum Industry, for example, has adopted the Norsok M-710 standard, while NACE International, which started out being known as the National Association of Corrosion Engineers, uses metrics of its own that gauge both static exposure to elevated pressure and rapid depressurization from elevated pressures.
Depending upon how familiar you already are with these concepts, those distinctions may mean a lot to you. For the uninitiated, learning all the various technical considerations can lead you down a deep rabbit hole if you attempt to cross-reference all the available materials and types of seals on the market.
But for most applications, the main takeaway is knowing that you must understand whether a seal will be subject to extreme pressures or not. If so, you will need to be a lot more diligent in ensuring you have the right piece for the job. Whereas more everyday uses will probably give you a wider range of options to work with.
Fluids and Viscosity
Naturally, seals are often used to create a secure, airtight barrier. This means they must stand up to liquids or prevent fluids from passing through one area of a machine to another. The type and material of the seal must be dictated by the type of fluid in question, as each will present different issues and complications.
Viscosity is a main consideration along with the chemicals contained within any given liquid that could degrade the seal material. Water and oil, for example, present different challenges for elastomers, and those that work well in these environments may not be appropriate for gels, greases, or muds.
Before selecting a material or type of seal, make sure you know exactly what fluids will be present in the system, what temperatures may occur, and how much pressure might be exerted.