One other environmental element that must always be addressed is the need for proper lubrication. As simple as it sounds, this really cannot be stressed enough. In almost any type of O-ring application, use of a proper lubricant — one that is chemically compatible with the seal, all system fluids, and all mating surfaces — is instrumental. This is true during both installation of the O-ring and its subsequent operation as a seal.

During installation, presence of a lubricant (such as oil or grease) simply helps ease the O-ring into place. You save both time and frustration. The chances of inadvertently damaging the seal are also minimized. If you don’t have to wrestle the O-ring into place, you’re less likely to accidentally nick or cut the seal’s surface. Lubrication helps seat static seals, and automated assembly would be impossible without the aid of some form of lubrication. But which form is best?

There are a variety of options. You can coat the outside of the O-ring with baked-on PTFE; this makes the seal super-slick. Or you can apply graphite, or even some molybdenum disulfide (MoS2). But while such external treatments definitely help during installation, they don’t last much beyond that point. “Moly” coatings rub off, and the baked-on PTFE soon flakes away.

Liquid lubricants are still another possibility. For example, International Products Corporation markets P-80, an emulsion formulated to provide temporary lubrication. Applied as a thin film on the surface of a rubber or plastic part, P-80 stays wet just long enough to allow the part to be installed.

But once the seal is successfully installed and the gland assembled, operational concerns take over. Break-out (startup) and running (dynamic) friction become the main concerns, especially in pneumatic equipment, plumbing devices, hydraulic valves and cylinders, or any application requiring manual operation. As during installation, surface treatments can help.

The most permanent surface treatment is chlorination, in which the O-ring elastomer (typically nitrile) is subjected to concentrated amounts of chlorine gas. This gas chemically attacks the seal’s surface, simultaneously making it both harder (by a few durometer points) and more slippery. Beneath the surface, the O-ring remains soft and resilient.

As a side effect of chlorination, the O-ring surface also develops numerous minute cracks. Because they are very small, however, these cracks will not impair the O-ring’s sealability. These tiny cracks are actually advantageous in that they can act as reservoirs for secondary external lubricants, such as oils and greases.

While chlorination is particularly helpful in reducing running friction, the additional step of treating the seal’s surface with oil or grease also facilitates installation and helps reduce break-out friction (otherwise known as static friction, or stiction). In addition, lubricants help protect the seal from oxygen and ozone damage. In vacuum applications, lubrication helps reduce the leak rate by filling in metal surface defects and O-ring micropores.

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