Radial Shaft Seal: 101

One of our application engineers just returned from a seminar that he gave on radial shaft seal function and application.  It was well attended and as always some interesting application questions were offered.  As he was describing a couple to me the thought went through my mind, “what were these guys thinking?” Seal selection was basically grab a catalog, find a size, check the material and see what’s in stock. Sigh… Too often we take a general description and dimension out of a catalog and hope it works. In fact, that actually does work, sometimes, as long as you at least know the basics.

So let’s look at some Radial Shaft Seal basics.

A Radial Shaft Seal, to simplify, is a seal meant to keep something in (oil, grease) or keep stuff out (dirt, water, contaminants) on a spinning shaft.

How that is accomplished depends on rotational speed, temperatures, pressure, and runout. In the ESP International Shaft Seal Handbook it explains how a shaft seal works and what the rotational element brings to the application. “Radial shaft seals prevent leakage through the generation of a pumping action at the interface of the seal lip and the shaft surface.”

Sealing Grease:  Because of the viscosity of most greases and their relation to the bearing in application, sealing the grease is usually fairly easy. Single lip, non-loaded seals often suffice and the use of the grease itself acts as an anti-contaminate tool as well as a bearing lubricant.  Spring loaded seals are used as well when conditions dictate.

Sealing Oil: This is a little more difficult in that the “pumping” effect is more prevalent with oil than grease.  Energized or loaded seals are usually needed to maintain enough seal force and contact. (Remember that runout thing I mentioned earlier?) Here is where geometry of the lips and environments become more of an issue.

Excluding Contamination:  Some of the toughest applications for radial shaft seals are the ones that require keeping out harsh contamination. From dust particles, to mud and water, fine dust and salts, you name it.  This can be accomplished with simple lip design with a second outward wiper or dust lip but when failure analysis results in a contamination cause, it can actually require multiple lines of defense utilizing labyrinths, multiple lips, different materials, both hard and elastic… the list goes on.

There are a lot of resources out there to help you. ESP International’s Shaft Seal Handbook is available on our website for easy access and contains some great application information to help you select the right profiles, materials and troubleshooting scenarios. Check it out. Need personal attention? Contact our Engineers to help with that critical application.

Axles, pumps, gear boxes, all come in different flavors.  Finding the right seal should be a priority – better now on the front end, than fixing it later.

Don Grawe is Director of Seal Markets for ESP International. He has over 20 years of experience in the seal industry serving the OEM industrial marketplace. You can learn more about ESP International at http://www.espint.com