  The experimental results for ZrZn$_{2}$, URhGe, and in some pressure ranges
also for UGe$_{2}$, have shown that the ferromagnetic superconductors are weak
itinerant ferromagnets. Guided by these results we describe the phenomenon of
coexistence between equal spin triplet pairing superconductivity (SC) and
ferromagnetism (F) using the extended Stoner model, which includes in
Hamiltonian the on-site Coulomb interaction, $U$, and occupation dependent
hopping integral. We use Hartree-Fock (H-F) approximation and the Green
functions technique. In the H-F approximation the on-site Coulomb interaction
plays the role of the on-site exchange (Hund's) field. All inter-site
interactions will have included the inter-site kinetic correlation,
$<c_{i\sigma}^{+}c_{j\sigma}>$, within the H-F approximation. We introduce the
pressure-dependence to the hopping integral. Numerical results are compared
with experimental data for ZrZn$_{2}$. The kinetic correlation creates the
superconductivity without help of negative values of Coulomb interactions. The
model can explain stimulation of triplet SC by the weak itinerant
ferromagnetism. This effect was observed experimentally in ZrZn$_{2}$.
Numerical analysis also confirms the experimental effect of decrease in
critical temperatures (Curie and superconducting) with increasing external
pressure.
