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Basic Concepts

The o-rings are circular-shaped seals, or torus, manufactured from an elastomeric compound. They are used for preventing liquid or gas to flow free. Correct sealing is reached by the effect of the restrain of the o-ring within its cavity or "gland"; as it squeezes and stretches inside its gland, it blocks all free spaces, therefore blocking all possible filtrations.

The most commonly used material for this type of seals is Nitrile, but according to specific needs for each application, o-rings can be manufactured in Silicone, Viton®, EPDM, among others. Hardness can also vary according to the functions the o-ring will perform, using harder compounds for performance in higher pressures and softer ones for lower pressures.

These are some of the advantages we can mention of using o-rings to ensure sealing properties:

• They bear a wide range of pressures, temperatures and tolerances
• They don't need fittings
• Light-weighted
• Occupy little space
• They can be used for static and dynamic applications.

Sizes

Regarding sizes, there are several norms for the standarization of the o-rings dimensions, usually relative to the country of origin. The more commonly used internationally are the following:

Country	Norm
United States Great Britain Germany Sweden France Japan	SAE AS-568A BS1806 - BS4518 DIN 3771 SMS 1586 NF T 47 501 JIS B2401-77