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A radial shaft seal (also known as a rotary shaft seal, rotary seal, or radial lip seal) is used in situations involving dynamic rotary motion. This type of seal can be used to achieve three different objectives in a machine:

  1. keep out contamination
  2. retain lubrication (oil or grease seals)
  3. separate different fluids. 

If the seal fails in any of these objectives, the result will be premature failure of the machine. That’s why the correct selection of a radial shaft seal is so very vital to machine performance and machine life.


In this blog post, we will look at three hints to help you select the correct radial shaft seal, and we will focus on applications involving a seal for a bearing.


Here’s the first hint . . .

Hint #1: Select the seal for the machine, not for the bearing.

Here’s the first hint: you don’t select a particular seal for a particular bearing, but rather select the seal for the machine itself. Just because you have a certain kind of bearing in place doesn’t mean that you have to use a certain kind of seal, nor is there one single seal design that works for every situation. You should select the seal based on its operating conditions.

And that leads us to Hint #2 . . .

Hint #2: There are 5 questions that need to be answered before selecting a seal.

Before you can select a seal, you need answers to all five of these questions:

  • What kind of lubrication will be used with the seal? (e.g., the use of oi or other low viscosity fluids may necessitate a spring energized lip)
  • Are there any potential compatibility issues between the seal and the process fluid?
  • Is the operating environment considered “dirty”? (if so, you may need an excluder)

Once these five questions are answered, you will have enough information to begin the process of selecting a seal.

Hint #3: Understand how radial shaft seals work.

Let’s take just a second to consider how these seals work. Radial shaft seals are placed between components in relative motion or between a rotating component and a stationary component, hence
their use with bearings.

As mentioned in the introduction, they are used to achieve three different objectives. Whether the seal
is excluding contamination, retaining lubrication, or separating two different fluids depends on how the
primary seal lip is oriented and whether or not the seal has an auxiliary lip. We mentioned that a dirty
environment may necessitate the use of an excluder. This is an auxiliary lip whose sole purpose is to
keep as much contamination out as possible. That’s why it would be recommended in a dirty


Radial shaft seals are a key component in many pieces of industrial machinery, and when properly
selected and installed will greatly extend the life of the machine. The keys to properly selecting a rotary shaft seal are to understand how they work, focus on the machine itself and not the bearing, and making sure you can answer five critical questions about the seal application.


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