We provide a integration of Navier-Stokes equations concerning the unsteady-state laminar flow of an incompressible, isothermal (newtonian) fluid in a cylindrical vessel spinning about its symmetry axis, say z, and inside which the liquid motion starts with an axial velocity component as well. Basic physical assumptions are that the pressure axial gradient keeps itself on its hydrostatic value and that no radial velocity exists. In such a way the Navier-Stokes PDEs become uncoupled and can be faced separately. We succeed in computing both the unsteady speed components, i.e. the axial vz and the circumferential v θ as well, by means of infinite series expansions of Fourier-Bessel type under time exponential damping. Following this, we also find the unsteady surfaces of dynamical equilibrium, the wall shear stress and the Stokes streamlines.