Seals modes of O-rings

Although O-rings were originally named for their circular cross-section, there are now variations in cross-sectional design.This shape can have different profiles such as an X-shaped profile, commonly known as an X-ring, Q-ring or by the brand name Quad Ring.When squeezed during installation, they seal through 4 contact surfaces 2 small contact surfaces on the top and bottom.This is in contrast to the relatively large single contact surface on the top and bottom of standard O-rings.X-Rings are most commonly used in reciprocating motion applications where they reduce running and breakout friction and reduce the risk of spinning compared to O-Rings.

There are also rings that have a square profile, often referred to as square cut, lathe cut, plate cut, or square rings.Square rings were introduced as an economical alternative to O-rings when O-rings were sold at a premium due to novelty, lack of efficient manufacturing processes, and high labor costs.Square rings are usually manufactured by molding an elastomeric sleeve and then cutting it with a lathe.This type of seal is sometimes less expensive to manufacture using certain materials and molding techniques (compression molding, transfer molding, injection molding), especially in small batches.The physical sealing performance of square rings is worse than O-rings in static applications, but not as good as O-rings in dynamic applications.Square rings are generally only used as energizers in cap seal assemblies in dynamic applications.Square rings are also more difficult to install than O-rings.Similar devices with non-circular cross-sections are called seals, packings or gaskets.

• Automotive cylinder heads are usually sealed with copper-plated flat gaskets.

• Knife edge pressed into copper gasket for high vacuum.

• Elastomers or soft metals that solidify in place are used as seals.

Failure modes 

O-ring materials can be affected by high or low temperatures, chemical attack, vibration, wear and movement.The elastic body is selected according to the situation.Some O-ring materials can withstand temperatures as low as −328.0 °F (−200 °C) or as high as 482 °F (250 °C).At the low end, almost all engineering materials become hard and cannot be sealed; at the high end, the material often burns or decomposes.Chemical attack can degrade the material, create brittle cracks or cause it to expand.For example, NBR seals will rupture when exposed to very low concentrations of ozone gas unless protected.Swelling through contact with low-viscosity fluids causes a dimensional increase and also reduces the tensile strength of the rubber.Other failures can be caused by using the wrong size ring for a particular groove, which can cause the rubber to squeeze out.Elastomers are sensitive to ionizing radiation.In typical applications,O-rings provide good protection against less penetrating radiation such as UV and soft X-rays, but more penetrating radiation such as neutrons can cause them to degrade rapidly. In such environments, use soft metal seals.

There are a few common reasons for O-ring failure:

1.Installation damage this is caused by improper installation of the O-ring.

2.Screw failure found on long stroke piston seals and to a lesser extent rod seals.The seal "hangs" at a certain point on its diameter (against the cylinder wall), sliding and rolling at the same time.This distorts the O-rings as the seal cycles and eventually creates a series of deep helical cuts (typically at 45 degree angles) in the seal face.

3.Explosive Decompression O-ring embolization, also known as gas expansion rupture, occurs when pressurized gas becomes trapped within the elastomeric sealing element.This expansion causes blistering and rupture of the seal surface.