Compression set
#1 What does the compression set stand for?
The compression set (DVR for short) provides information about the resilience of an O-ring. In other words, the extent to which an O-ring returns to its original round shape after the O-ring is no longer under pressure.
The compression set is one of the most important specifications and can be found on every material data sheet.
It is measured by pressing an O-ring or test specimen for a certain period of time at an elevated temperature. The O-ring is then released and the extent to which the O-ring has been permanently deformed is checked.
How long the O-ring is pressed under temperature and how high the temperature must be is incomprehensibly not specified as a standard. This requires a critical eye on the part of the user or designer.
#2 What are suitable parameters for measuring the compression set?
NBR = 22 hours / 100°C
EPDM = 22 hours / 125°C
EPDM peroxide cross-linked = 22 hours / 150°C
SILICONE = 22 hours / 175°C
FKM = 22 hours / 200°C
FFKM = 70 hours / 200°C
#2 What is a good value for a compression set?
A good compression set lies in usually between 10% and 25%. Above a value of 40%, it becomes critical for the longevity of the O-ring.
Note: For O-rings made of pure PTFE or FEP encapsulated O-rings usually lack the specification of the
compression set, as the materials are not elastic and can be deformed after do not return to their shape after pressing.
