Oil seals and grease seals have a flexible lip that rubs against a shaft or housing to prevent the leakage or ingress of fluids and dirt.

For proper installation, the seal lip should point towards the medium being contained. Some oil seals and grease seals have a spring to help keep the lip in contact with the shaft.

Oil and grease seals are used to retain or separate lubricants or fluids. These seals are primarily used for rotary applications only.

Types of Oil Seals and Grease Seals

The seal type for oil seals and grease seals can be oil seals or other types. An oil seal can also called flexible lip, radial lip, or rotary shaft seal. Common configurations include single lip, double lip, triple lip, and four or more lips.

Bearing Isolators

Bearing isolators are dynamic seals designed to protect bearings from outside contaminants. They are comprised of a rotor (rotating) and stator (stationary) member. Some bearing isolators are of labyrinth construction while others use O-rings or other positive seals.

Other types of oil seals and grease seals include:

• Single lip oil seals
• Double lip oil seals
• Metal cased
• All rubber or polymer
• Internal orientation
• External orientation
• Axial orientation
• Spring-energized

Specifications

Common specifications include sealing orientation, construction parameters, dimensions, service limits, and lip materials.

Sealing Orientation

The sealing orientation and direction is important to consider for oil seals and grease seals.

• Rod seals, also referred to as shaft seals, are radial seals. The seal is press-fit into a housing bore with the sealing lip contacting the shaft.
• Piston seals are radial seals. The seal is fit onto a shaft with the sealing lip contacting the housing bore. V-rings are considered external lip seals.
• A symmetric seal is symmetrical and works equally well as a rod or a piston seal.
• An axial seal seals axially against a housing or machine component.

Construction Parameters

Important seal construction parameters to consider include metal casings, and dual lip elements.

Dimensions

• Shaft outer diameter or seal inner diameter
• Housing bore diameter or seal outer diameter
• Axial cross section or thickness
• Radial cross section

Service Limits

• Maximum operating speed
• Maximum operating pressure
• Vacuum rating
• Operating temperature

Lip Materials

• Ethylene acrylic
• EDPM
• Fluoroelastomer
• Fluorosilicone
• Nitrile
• Nylon or polyamide
• Polychloroprene
• Polyetheretherkeytone
• Polyoxymethylene
• Polytetrafluoroethylene
• Polyurethane
• Urethane
• Natural rubber
• Sintered bronze
• Cast iron
• Stainless steel
• Felt
• Leather

Many seal manufacturers use their own proprietary material. Consult with manufacturer for proprietary material specifications.

Features

Common features for oil seals and grease seals include spring loaded, integral wiper, and split seal.

Standards

FORD ESE-M8G66-A - Oil seal, polyacrylic rubber

MIL-S-21558 - Oil seals, plain or plain encased

Image credits:

SKF/North America | KC Seals, Inc. | Daemar Inc.