Oring, O-ring

The effects of temperature changes from +18°C to +121°C (-65°F to +250°F) on the performance of Oring seals depends upon the seal material used. Synthetic rubber can be made for continual use at high or low temperatures, or for occasional short exposure to wide variations in temperature. At extremely low temperature the seals may become brittle but will resume their normal fl exibility without harm when warmed. Prolonged exposure to excessive heat causes permanent hardening and usually destroys the usefulness of the seal. The coeffi cient of thermal expansion of synthetic rubber is usually low enough so that temperature changes present no design diffi culties.

Note: These points are general statements and there are, of course, numerous exceptions. Details of Oring seal design in regard to particular situations are discussed in the following sections: Applications, Elastomers, Factors Applying To all Oring Types, Static Oring Seals, and Dynamic Oring Seals can be referenced as needed.

O-ring seals are extremely dependable because of their simplicity and ruggedness. Static seals will seal at high pressure in spite of slightly irregular sealing surfaces and slight cuts or chips in the seals. Even when broken or worn excessively, seals may offer some measure of fl ow restriction for emergency operation and approaching failure becomes evident through gradual leakage. 

In a seat seal, the O-ring serves to close a fl ow passage as one of the contact members. The motion of closing the passage distorts the O-ring mechanically to create the seal, in contrast to conditions of sealing in previously defi ned types. A sub-classifi cation is closure with impact as compared with non-impact closure. Examples of a seat-seal include O-ring as a “washer” on the face of a spiral threaded valve, a seal on the cone of a fl oating check valve, and a seal on the end of a solenoid plunger.