Intermediate stage of the process describing bottleneck in some storage system

A real storage system containing production, transport, store and receiver is considered. The bottleneck in the system is defined. For the intermediate stage of the process z(t) controlled by the Markovian production process y(t) formulae for conditional probabilities and differential equations satisfied by the density functions of probability fk (z, t) of two-dimensional stochastic process (z(t), y(t) are formulated for the intermediate stage of the process describing the bottleneck.