O-rings are solid-rubber seals that are shaped like a doughnut. When pressed between two mating surfaces, O-rings block the passage of liquids or gases. O-rings can form a static or dynamic seals. A static seal is where the O-ring does not move and is used simply for containing pressure or maintaining a vacuum. Dynamic seals can be reciprocating (like a piston and cylinder), or rotating (shaft rotating in a housing). Axial squeeze and radial squeeze are two methods for applying an O-ring.
Q & A on O-rings
We asked our users for their input on O-rings. Here are the results of 505 users familiar with O-rings.
Who Took Our Poll? | Design Trends | Applications and Use | Features | Buying AdviceDesign TrendsTop
Molding process to eliminate flash in the center of the cross-section coincident to the the outside and inside diameters. Evolution of compounds less prone to explosive decompression, higher pressure applications, and tolerance to wider range of media.
Applications and UseTop
Pneumatic pistons, static seals/glands-high pressure gas applications, hydraulic cylinders, valve seats, pneumatic & hydraulic actuators, pilot valves, reciprocating actuators, bumpers/shock absorbers and motion transmission (like a belt and pulley system).
Water, Hydraulic Fluids, Gas & Oil, Food and life sciences, Chemical Industry, Agricultural, Pulp and Paper, Mining, Power Generation,Valves,Flanges, Dispensing Equipment, Hydraulic Cylinders, Transportation Industry.
Typically, as o-ring I.D. increases, the cross-sectional diameter increases. We have many applications requiring large I.D. o-rings with smaller C-S diameters than available, forcing us to make our own sizes. We'd rather not do this as some applications are to seal between mating parts operating at up to 10,000 psi. atomizing applications.
In jack assembly of floor crane, O rings were used as jack seals inserted in a Teflon ring machined locally. Ready made O-rings were fitted on the PTFE ring machines with the grooves for outside and inside sealing. Assembly worked successfully for the emergency maintenance job.
FeaturesTop
Unification of material grades into a common standard to enable the purchase of similar 'o'-rings from different manufacturers. It's a challenge at the moment to identify, for instance, the grade of 'chemraz' that is an equivalent to the 'kalrez' you have specified.
O-ring should be replaced after any maintenance even if deterioration is less. Thickest size O-ring is preferable for a particular size of shaft / housing. Exposure to ozone, air, sunlight should be avoided to enhance O-ring life. Entry of O-ring should be smooth to avoid cuts. Light lubrication (suitable one) should be applied to O-ring during installation.
Do not remove tag from the O-Ring bunch or envelop till you are ready to use. Do not apply " Any" lubricant on O rings after fitting in the grooves. If it is required to be applied it should be specific for the O-Ring Material and the process service. O-Ring materials, which are not compatible with mineral oils, shall not be coated with Oil based grease etc.
In high pressure applications, even static sealing rings are moving and changing shape when pressurized and de-pressurized. Surface finish and the use of support rings can improve service life. A lubricant can also help reduce the wear of the base mat'l. and o-ring skin.
Buying AdviceTop
Do not leave the specification of a seal or o-ring until the end of the design process. Work with your seal supplier to determine the correct seal choice as early as possible during your design process. You can then incorporate design features that allow correct installation and choice of 'standard' products to avoid tooling costs etc.
Stick to standards whenever possible. Use the standards on your internal drawings or in your business system master descriptions. Bear in mind that some materials [liquids] "age" and their pH changes... So the O ring of choice must be compatible with "on-spec" fluid, and aged fluid as well.
O-ring should be of a reputed company. Material selection has to be based on your application. Exposure to ozone, air, sunlight should be avoided to enhance life. For dynamic application, squeeze should be less i.e. between 10 to 20%.
