Lip Seals: What They Are and When to Use Them

Spring-energized seals by Monroe Engineering

When shopping for seals, you may encounter lip seals. They are commonly used in machinery. Motors and other machines often contain rotating shafts. Lip seals are placed around these rotating shafts to prevent oil, coolant or other fluids from leaking. For a better understanding of lip seals, keep reading.

What Are Lip Seals?

Lip seals are circular, ring-shaped mechanical seals that are used to protect against leaks. Also known as lip rings, they are characterized by a notched perimeter.

If you inspect the inner perimeter of a lip seal, you’ll notice a notch or “lip.” This notched inner perimeter is placed around a rotating shaft where it serves the following two purposes:

  1. It traps lubricant, such as oil, to ensure a smooth rotation.
  2. It keeps dirt, dust and other contaminants out.

What Are Lip Seals Made Of?

Lip seals are made of an elastomeric material. Like with other types of seals, including O-rings, they are often exposed to heat and pressure. Therefore, they must be able to withstand heat and pressure without leaking. Elastomeric materials are characterized by a polymer-based construction with high elasticity. Even when exposed to heat and pressure, they won’t fail.

Some lip seals are made of TFE/P rubber, whereas others are made of fluorosilicone or Neoprene. Regardless, their elastomeric construction allows them to withstand heat and pressure — all while sealing the rotating shaft with which they are used.

How Lip Seals Differ From O-Rings

While they both feature a similar shape, lip seals and O-rings aren’t the same. Lip seals are distinguished from their O-ring counterparts by their notched perimeter. O-rings consist of a solid and smooth ring-shaped piece of elastomeric material. Lip rings, in comparison, consist of a ring-shaped piece of elastomeric material with a notched inner perimeter.

When to Use Lip Seals

Lip seals are typically used in sealing applications involving rotating shafts. If you’re looking for a mechanical seal to use with a reciprocating part, you may want to choose a traditional O-ring. For a rotating shaft, on the other hand, you should typically choose a lip seal.

Rotating shafts are susceptible to friction-related damage. As the shaft rotates, it may generate friction while subsequently promoting premature wear and tear. Lip seals won’t interfere with the shaft’s rotation. Rather, lip seals are designed to reduce friction by retaining lubricant and warding off contaminants.