What is an O-Ring?

　　An O-ring is a doughnut, or torus shaped seal typically used to prevent the passing of air or fluid. In other words, O-rings are used to keep fluid or air IN or OUT of a defined space. For example, My underwater camera uses O-rings to keep water out and my SCUBA regulator uses O-rings to prevent precious air from escaping. O-rings can be used for more than preventing air or fluid from passing, they are also used as drive belt, decorative objects on furniture, cups and automotive parts and also used as body jewelry.

　　How Does and O-ring Seal Anyway?

　　Before we go over types of materials, hardness, sizes and tolerances of O-rings lets talk about how the O-ring actually seals. Basically an O-ring is used to block a pathway that fluid or air may escape through. O-rings are usually put into a groove to hold them in place and then squeezed between two surfaces. When you squeeze the o-ring between two surfaces you are taking up the clearance and blocking the pathway that the fluid or air wants to escape through. When an O-ring is squeezed the rubber has a memory. In other words it wants to go back to its original shape.

　　This memory is how the O-rings seal under low to no pressure. When pressure is applied to the system this also helps the O-ring seal by pushing the o-ring against the groove wall opposite the direction of the pressure and forcing it expand perpendicular to the direction it is being squeezed by the pressure. Wow, what a mouth full. Lets see if we can explain that a little more simply. Take a water balloon, for all practical purposes water is not compressible. When you squeeze the water balloon between your hands it expand in the opposite direction. Go ahead and get a water balloon and try it.

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