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.
