The mechanical seal has many variations and configurations depending on its application. The distinctions that can be made are:
Dependent or independent of the direction of rotation.
Dipendente o indipendente dal senso di rotazione. A characteristic example is the conical spring mechanical seal, in which the motion of the rotor (shaft) is transferred directly to the seal itself, bringing it into rotation. In this specific case, the seal will only function if it is produced in the correct direction of rotation. Mechanical seals with several springs (multi-spring), leaf springs, or bellows (mostly metal) can, on the other hand, work in both directions of rotation
Balanced or unbalanced The most important of the principles that characterize a mechanical seal is whether its geometric structure is balanced. A balanced mechanical seal is one in which, during the design phase, the operating pressure that must be satisfied has been taken into account, thus attempting to ensure that the pressure in the seal chamber helps to close the sliding faces. Balancing is carried out by calculating the difference of the surfaces placed under pressure (positively, if it’s in favor of thrust, and negatively, if for example the seal must be applied externally to the process). The calculation of balancing can be summarized by the following formula:
B = (Do2 – Db2)/(Do2 – Di2) for external mechanical seals
B = (Db2 – Di2)/(Do2 – Di2) for internal mechanical seals