A film thickness equation for mechanical face seals

Due to environmental demands it is important for mechanical face seals to minimize the leakage. Because the leakage due to pressure flow is proportional to the third power of the separation of the faces, it is therefore necessary to reduce this separation in order to minimize the leakage. Geometrical features (coning and waviness) in combination with the operational conditions, do affect the separation between the faces. In order to know the separation between the faces, a film thickness equation is required, which is a function of geometrical features (coning, waviness and face dimensions) and the operational conditions (fluid pressure, cavitation pressure, rotating speed and viscosity of the fluid). In this paper a film thickness equation has been derived, based on dimensionless numbers, for a seal combination where one face is flat and the other may have coning and/or waviness. The dimensionless numbers contain the aforementioned parameters. Furthermore, the effect of the waviness, coning, seal dimension and cavitation pressure on the leakage, the friction and the film thickness are presented for three different lubrication modes, i.e. a) hydrostatic, b) hydrodynamic and c) combined hydrostatic and hydrodynamic.