Deflection of torque transmission. High demands are placed on the transmission of torque between the seal face and drive collar by frequent start-ups and changes in the direction of rotation, and by torsional vibrations owing to alternating moments of friction. With some types of torque transmission, e.g. torque transmission by certain shapes of bead (see photo), the deformations and loss of material caused by the resultant impact loads can impair the function of the mechanical seal up to its sudden failure. Once the beads are sheared off, the seal face is no longer driven, the secondary seal on the shaft side is destroyed, and the leakage increases abruptly.

With torque transmission by pin and slot (see photo), the axial mobility of the face housing is lost – and with it the contact between sealing faces – when the pin wears a recess in the slot wall. Once again the leakage increases considerably. An example of a very rugged form of torque transmission is a round pin engaged in a slot in the hard seal face (see photo). Wear is noted only as a certain flattening of the pin. It is impossible for the seal face to "catch", and loss of contact between sealing faces is thus ruled out. As a further benefit, the initially linear and subsequently planar point of contact between the seal face and drive collar guarantees optimum mobility and adaptability of the seal face.

Beginning of shearing at the torque transmission on a bead

Favourable torque transmission, maximum mobility of seal face