We consider the Elrod-Adams model extending the classical lubrication Reynold equation to the case of the possible presence of a cavitation region. We show that the behaviour of the pressure and saturation depends crucially of the behaviour of the separation $h(t,x,y)$ among the two surfaces. In particular, we exhibit some simple formulations for which we prove (rigorously) that a cavitation region is formed instantaneously (even for initially saturated flows). Some numerical experiences are also given.
