When Exactly Is An O-Ring Not An O-Ring?

ibtinc
August 7, 2009

So when is an O-Ring not an O-Ring?

When it’s a D-Ring, an X-Ring, a Square Ring, or a Back-Up Ring, of course! The O-Ring is the workhorse of the “Ring” family, but its many relatives also perform important and valuable roles in industrial sealing applications.

We’ll cover the popular variations of the O-Ring in this article, but remember to always consider all of your application’s parameters to make sure you select the right compound and size for any of these styles. Refer to the Dichtomatik O-Ring Handbook for more information.

Let’s examine the different types of rings that can be used in place of or along with an O-Ring:

	D-Ring Where the standard O-Ring is noted for sealing in static applications, the D-Ring is used in reciprocating applications because it resists spiral failure. The flat side that forms the “D” shape keeps the ring from rolling, where a typical round O-Ring will start twisting or rolling under movement and will eventually fail. The D-Ring can be used to seal on the ID or the OD, depending on the need.
	X-Ring Like the D-Ring, the X-Ring is well-suited for serving in dynamic applications. In fact, the X-profile reduces friction while still sealing and resisting spiral failure, and should be specified when drag or resistance from a sealing surface may impact the precision of a moving component.
	Back-Up Ring The name of these rings describes them perfectly – they provide “back-up” to an O-Ring in an application where high pressure may cause the O-Ring used for sealing to extrude from its gland (refer to the Dichtomatik O-Ring Handbook for proper gland design). They have a flat side plus a contoured side that matches the curve of the O-Ring they are matched with and are typically made from stiffer compounds like NBR 90, PTFE or Nylon.
	Square Ring The least glamorous of the “ring” family, the Square Ring is perfect for the “set it and forget it” static sealing application. And because Square Rings can be lathe cut from rubber gasket material, they are often less expensive then comparably sized O-Rings, especially in large ID applications.

Dichtomatik offers these different sealing ring styles in AS-568 sizes and standard compounds “off the shelf” and will also quote molded product for higher quantities in non-standard sizes and compounds. If a single ring or smaller quantities of a specific size are needed, Dichtomatik’s Splicing Center can custom make the ring from cord stock. Contact IBT with your special requirements.

A recent PrimeMover article talked about the different materials used in the production of O-rings and the importance of selecting the correct material for critical industrial applications. It explained how heat, steam, oils or chemicals, and pressure can rapidly degrade a standard O-Ring and how to select the right material for your application.