The concern with extrusion is that at a higher pressure (especially with soft elastomer O-rings), the O-ring can be forced into the small gap between the piston or rod, and the bore. However, it is not typically a concern for face type seals as the metal parts to be sealed are in contact, line-to-line. Elastomers can have coefficients of thermal expansion 7 to 20 times higher than that of metals, such as steel.Įxtrusion is a concern for radial seals where there is gap between the piston and the bore or between the rod and the bore. It is important to note that there are significant differences in the coefficients of thermal expansion between the O-ring material and the groove materials. This is a general rule and there may occasionally be exceptions. For dynamic applications, 10 or 15 % volume swell is a reasonable maximum, unless special provisions are made to the gland design. For static O-ring applications volume swell up to 30 % can usually be tolerated. Volume change is the increase or decrease of the volume of an elastomer after it has been in contact with a fluid, and is measured in percent (%). Groove fill of the installed O-ring should not be more than 85 % to allow for possible O-ring thermal expansion, volume swell due to fluid exposure and effects of tolerances. It is important to consider the groove fill of the installed O-ring to avoid detrimental effects on radial sealing performance. smaller than 20 mm, this is not always possible due to tolerance issues, which can result in a greater O-ring O.D. greater than 250 mm, or 5% for O-rings with an I.D.

should not exceed 3% of the rod gland diameter for O-rings with an I.D. The O-ring's outside diameter (O.D.) should be at least equal to or larger than the rod gland diameter to give interference on the O-ring's O.D.

In dynamic applications, it is important to keep the maximum stretch to 5% or less to avoid detrimental effects on sealing performance.įor hydraulic and pneumatic rod sealing applications To minimize this range of stretch (including the maximum stretch) it is necessary to minimize the tolerance of the piston gland diameter, and have a less stringent requirement for the minimum O-ring stretch. For O-rings with an inside diameter smaller than 20 mm, this is not always possible as it can result in a wider range of stretch.

The O-ring's inside diameter (I.D.) should stretch between 2% and 5% for dynamic applications and between 2% and 8% for static applications. Ceramic Components Mechanical Seals Protector Productsįor hydraulic and pneumatic piston sealing applications

Difference between oil seal and o ring