What Is a Lip Seal? | Discover what a Rotary Shaft Seal or Oil Seal is

15 April 2019
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The term lip seal might conjure up images of an amazing way to deal with people who talk too much, but the real function of this seal is a bit more mundane. So what is a lip seal? Lip seals serve to protect lubricated moving parts and they do this by keeping the lubricant inside the bearing, and keeping contamination from dirt or other liquids out. The term lip seal is generally used to refer to what is correctly known as rotary shaft seals or oil seals or a radial shaft seal.

Oil seals are commonly used in sealing rotary elements such as hydraulic pumps and valve stems. Typically they must withstand the strain of ongoing movement and conditions where they are exposed to grit and contamination.

Long ago, they were actually made of rawhide, but today, oil seals are very sophisticated, and various types of rubber are used to make them. Modern rotary shaft seals can be fairly complex with various parts and contacting patterns. They can be spring-loaded or not, as they are used in a wide variety of applications, oil seals come in a variety of specifications, which can be found here.

Replacing an Oil Seal or Rotary Shaft Seal


Even the best seals don’t last forever. What is an oil seal’s normal life span? It depends on the environment and the amount of wear and tear it experiences. The best practice is to be proactive and replace seals before they go. Monitor seals regularly and when you see visible damage, replace them.

Be sure the replacement seal is of the correct specifications and the assembly lubricant is compatible with the lubricant currently being used in the application. First, check the new oil seal thoroughly to ensure it is free of damage, paying extra attention to the elastomer and the case. If it has a spring, check that too.  

Installing the new rotary shaft seal incorrectly will compromise the seal, risking damage to the equipment and impairing its function. Having the right seal installation tool such as a seal digger is critical for this. It is a job that demands precision. If equal pressure is not applied during installation, the seal will be uneven and will not function properly.

What Is an Oil Seal/Rotary Shaft Seal’s Main Weakness?


High temperatures are an oil seal’s main challenge. When you make a purchase, it is important to ask what is the oil seal’s maximum operating temperature to confirm it is suitable for the application. High temperatures thin the lubricant, causing the rotary shaft seal to dry out and become brittle. Excessively cold temperatures can have the same effect. Insufficient oil is another common problem.

Oil seals are an effective way to protect moving parts. They keep lubricant in place and ensure that other liquids and debris does not get in. Keeping extra rotary shaft seals on hand and proactively replacing them before they are worn out can prevent damage to machinery and interruptions to productivity.

Discover our rotary shaft seals specification sheets here. To request more information regarding oil seals or rotary shaft seals, please fill in the product information request form here.