As shown in Illustration 5.2, the extrusion limit of o-rings under pressure is determined by the size of the diametrical clearance gap and the hardness of the o-ring material.
If the point representing the intersection of the lines of sealed pressure and diametrical clearance falls to the right of the material's hardness curve, either the material hardness must be increased, or back-up rings will be required.
Examples
-
Material hardness of 70 Shore A. Sealed pressure of 1,000 psi. Diametrical clearance of .016″.
Intersection of sealed pressure and diametrical clearance lines falls to the right of material hardness curve. Increase hardness, use back-up rings, or reduce diametrical clearance.
-
Material hardness of 80 Shore A. Sealed pressure of 1,000 psi. Diametrical clearance of .016″.
Intersection of sealed pressure and diametrical clearance lines falls to the left of material hardness curve. This is acceptable.
The use of two back-up rings (one on each side of the rings) is preferred. This will help prevent installation errors, assuring that the clearance gap is always correctly blocked, regardless of pressure direction.
Illustration 5.2 (Extrusion Limit)
