What is an O-Ring?
An O-ring is a torus, or doughnut-shaped ring, generally molded from an elastomer, although O-rings are also made from PTFE and other thermoplastic materials. O-rings are used primarily for sealing.
O-rings are designed to be seated in a groove and compressed during assembly between two or more parts, creating a seal at the interface. The seal closes off a passageway and prevents an unwanted loss or transfer of fluid. It consists of two elements, the o-ring itself and a properly designed gland to contain the elastomeric material.
O-rings are one of the most common seals used in machine design because they are inexpensive and easy to make, reliable, and have simple mounting requirements. They can seal tens of MPA (thousands of psi) pressure.
Advantages of O-Rings
- They seal over a wide range of pressure, temperature, and tolerance.
- Ease of service, no smearing or retightening.
- No critical torque on tightening, therefore unlikely to cause structural damage.
- O-rings normally require very little room and are light in weight.
- In many cases, an O-ring can be reused, an advantage over non-elastic flat seals and crush-type gaskets.
- The duration of life in the correct application corresponds to the normal aging period of the O-ring material.
- O-ring failure is normally gradual and easily identified.
- Where differing amounts of compression effect the seal function (as with flat gaskets), an O-ring is not affected because metal to metal contact is generally allowed for.
- They are cost-effective.
O-Ring Sealing Types
Static - application where there is little or no relative motion between the mating surfaces.
Dynamic - the o-ring functions between surfaces with definite relative motion, such as seal on the piston or hydraulic cylinder. Of the two types, dynamic sealing is more difficult and requires more critical design work and materials selection.
O-ring selection is based on chemical compatibility, application temperature, sealing pressure, lubrication requirements, quality, quantity, and cost.
Base polymers include: