Compound Hardness
In the majority of cases a 70° Shore A quality will be satisfactory.
Though not really necessary, softer O-Rings from 40° to 60° Shore A are
often installed for sealing at low pressures or a vacuum. O-Rings harder
than 70° Shore A (eg 90° Shore A) should be used, preferably with backup rings,
at high pressures to avoid the O-Ring being extruded through
the clearance.
For the selection of compound hardness the following facts should be
considered:
- If pressures are low, hard O-Rings seal less perfectly than softer O-Rings;
- To reach the amount of diametrical compression desired, hard O-Rings require
more load than soft O-Rings.
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