Seales on Seals: An O-Ring Guide

Rotating equipment (such as pumps, motors, mixers, and agitators)is used in virtually every process industry. Most rotating assets have more than one O-ring installed. But what is an O-ring, and how do you decide which type an asset needs? This article answers all these O-ring questions and more.

What Is an O-Ring?

An O-ring is a mechanical gasket with a round cross section. The name O-ring comes from the fact that the item is shaped like the letter O and looks like a ring.

An O-ring is a closed loop circular band that. In most cases, it is made from an elastomer or other pliable material. Elastomers may be natural (often latex-based) or synthetic (made from petroleum). Some synthetic materials are an American Society for Testing and Materialsclass of fluorinated, carbon-based synthetic rubber, commonly known as fluoroelastomers.

what is an O-ring?
O-ring examples

What Are O-Rings Used for?

O-rings prevent fluid (gas or liquid) leaks in static and dynamic applications. The material of each O-ring depends on the application.

Some of the things that need to be considered are:

  • Is the O-ring static or dynamic?
  • To what temperatures will the O-ring be exposed?
  • What is the rotational speed (if installed in a dynamic application)?
  • To what pressures will the O-ring be exposed?
  • What is the chemical make-up of the fluid being sealed (abrasive, contains fibers, changes state)?

If unfamiliar with O-rings or if you have an uncommon application, you should consult your O-ring manufacturer for assistance.

How Are O-Rings Measured or Sized?

O-rings fit inside a gland or cavity designed to hold a specific sized O-ring. To determine the size needed, you will need the cross section and inside diameter of the application in order to find the correct O-ring. Consult your O-ring handbook for details on determining the cavity dimensions and the specific O-ring size that corresponds with the cavity dimensions you need or have. This applies for both static and dynamic O-rings.

You also have to determine the squeeze of the O-ring. The squeeze is the minimum and maximum compression required for your application. Consult your O-ring handbook for details on determining the squeeze for the specific O-ring size that corresponds with the cavity dimensions you need or have.

Do O-Rings Need Lubrication?

Lubricants are commonly used on O-rings at assembly to help protect the O-ring from damage caused by abrasion, pinching, or cutting. Lubrication also helps protect some polymers from degradation caused by atmospheric exposure. The presence of a lubrication helps extend the service life of the O-ring.

The chemical makeup of the lubrication needs to be compatible with the application and the O-ring materials of construction, so consult your manual. If no lubrication or the wrong lubrication is used, failure may occur.

How Do O-Rings Fail?

O-rings fail for many reasons. Some of the most common are:

  • Chemical incompatibility with fluid being sealed
  • Excessive vibration
  • The application’s pressure exceeds the pressure limits of the material of construction
  • The application’s temperature exceeds the temperature limits of the material of construction
  • Improper installation
  • Rough, worn, or sharp surfaces
  • Inadequate lubrication
  • Wrong lubricant selected

How Do I Know if My O-Ring Is Failing, and When Should I Replace My O-Ring?

A common indicator of O-ring failure is visible leakage, odor, and equipment performance issues. O-rings should be replaced for many reasons, including:

  • The O-ring can no longer provide an effective seal
  • Whenever the equipment is removed for maintenance
  • When the application has changed and is no longer compatible with the O-ring material


This Seales on Seals blog attempted to help you understand:

  • What is an O-ring?
  • What is an O-ring used for, and how do you select one?
  • Do O-rings need lubrication?
  • Why do O-rings fail , and when should you replace it?

Always consult with your manufacturer when you have questions or concerns.


Parker Hannifin Corporation. (2007). Parker O-Ring Handbook. Lexington, Kentucky: Parker Hannifin Corporation.

Volk, M. (2014). Pump Characteristics and Applications. Boca Raton, Florida: CRC Press.

Fluid Sealing Association. (2000). Mechanical Seal Handbook. Wayne, Pennsylvania: Fluid Sealing Association;

About the Author
Thomas (Tommy) Seales is the Mechanical Seal Division Product Manager for SealingEquipment Products Company (SEPCO). He is primarily responsible for managing theengineering department and overseeing new product development. His responsibilities alsoinclude providing any and all domestic and international technical support for the distributor
and outside salesforce for SEPCO. Seales has worked at SEPCO for more than 42 years and hasbeen the product manager of the mechanical seal division for 35 years. He is an honorarylifetime member of the United Who’s Who Registry of Executives and Professionals. Sealesmay be reached at

Mikal Hayes is an applications engineer for SEPCO and a member of the Processing Editorial Advisory Board. Hayes’ roles include designing, analyzing and testing new mechanical seals, bearing isolators and air seals — with a focus on product research and development. Hayes received his BSME from the University of Alabama at Birmingham (UAB).