  We consider the model of i.i.d. first passage percolation on Z^d, where we
associate with the edges of the graph a family of i.i.d. random variables with
common distribution G on [0, +$\infty$] (including +$\infty$). Whereas the time
constant is associated to the study of 1-dimensional paths with minimal weight,
namely geodesics, the flow constant is associated to the study of
(d--1)-dimensional surfaces with minimal weight. In this article, we
investigate the existence of the flow constant under the only hypothesis that
G({+$\infty$}) < p c (d) (in particular without any moment assumption), the
convergence of some natural maximal flows towards this constant, and the
continuity of this constant with regard to the distribution G.
