THE ANNALS OF UNIVERSITY “DUNĂREA DE JOS “ OF GALAŢI FASCICLE VIII, 2005, ISSN 1221-4590 TRIBOLOGY 79 INTERNAL MECHANICAL SEALS WITH IMPULSES: A HYDRODINAMICAL APPROACH Lucian TUDOSE, Marius PUSTAN Technical University of Cluj-Napoca, Romania lucian.tudose@omt.utcluj.ro ABSTRACT In this paper a hydrodynamic approach of internal mechanical face seals with impulses is presented. Dimensionless parameters and cylindrical coordinates were used in order to adjust the Reynolds equation to the actual case. The pressure distribution across the faces of the seal, the leakage debit, the bearing force, and the average coefficient of friction are computed. KEYWORDS: mechanical face seals, pressure distribution, leakage debit, coefficient of friction. 1. INTRODUCTION The main parts of a mechanical face seal with impulses are the stator and the rotor (Fig. 1). On the front face of the stator are milled several chambers (1), since on the front face of the rotor are milled an even number of channels (2). Periodically, during an operating cycle, the channels are connected by the chambers of the ring-stator through the meaning of the fluid that has to be sealed. In the very moment when the channels on the rotor are overlapping the chambers belonging to the stator, the pressure in the chambers increases. This fact leads to the spacing of the stator from the rotor. In the very next acting phase, when the channels are moving away from the chambers, the pressure in the chambers decreases and that leads to the approaching of the stator from the rotor. In this way, the ring-stator has to support weak perturbations. The fact that the number of channels on the rotor are even is very important. Let’s examine the case with three channels on the rotor. Supposing that on the upper side of the rotor face (relating to the rotation axis) there are two channels overlapping the corresponding chambers on the stator, results that on the lower side of the rotor there is only one channel overlapping a chamber on the stator. Consequently, the force acting on the upper side of the rotor (stator) is twice as the force acting on the lower side of the rotor (stator) and both parts are forced to slope within the limits of their fits. Note that the higher force acts on the same point on the rotor and rotates with respect to the stator. That means that the normal versors of the faces of the stator and the rotor respectively, remain coplanar. Since this kind of seals are used for very high aggressive, toxic, hot or abrasive fluids, the most important parameters in describing the behavior of a mechanical face seal with impulses are the leakage debit and the coefficient of friction between the layers of the fluid and the faces of the rotor (or stator). Both these parameters should be minimal in order to avoid harmful leakage and earlier wear. Fig.1. Mechanical face seal with impulses. ROTOR STATOR 1 2 p e p i