2. For dynamic seals, it can be divided into three situations; reciprocating motion generally takes W=10%~15%. When selecting the compression ratio of the rotary motion seal, the Joule heating effect must be considered. Generally speaking, the inner diameter of the rotary motion O-ring is 3%-5% larger than the shaft diameter, and the compression rate of the outer diameter W=3%-8%. In order to reduce frictional resistance, O-rings for low-friction movement generally choose a smaller compression rate, that is, W=5%-8%. In addition, the expansion of the rubber material caused by the medium and temperature should also be considered. Usually outside the given compression deformation, the maximum allowable expansion rate is 15%. Exceeding this range indicates that the material selection is inappropriate, and O-rings of other materials should be used instead, or the given compression deformation rate should be corrected.