Context : Intermediate and high velocity HI clouds rain onto the plane of our Galaxy .
They are observed at heights of between 500 and 1500 pc , falling onto the Galactic plane at velocities from 50 to 140 km s ^ { -1 } .

Aims : To explain the origin of these clouds , we present a galactic fountain model , driven by the wind from a super stellar cluster ( SSC ) .

Methods : We solve the equations for a steady , radiative de Laval nozzle flow .
We consider two effects not considered previously in astrophysical nozzle flow models : cooling functions for different metallicities , and the direct action of the galactic gravitational field on the gas flowing along the nozzle .

Results : For an adiabatic nozzle flow , the gravity acting directly on the gas within the nozzle “ stalls ” the nozzle flow for initial wind velocities lower than the escape velocity from the Galaxy .
For the same wind velocity , a radiative nozzle flow stalls at lower altitudes above the galactic plane .
We find that SSC winds with velocities of v _ { w } = 500 - 800 km s ^ { -1 } produce nozzles stall at heights of x _ { m } = 1 - 15 kpc .
The stalled nozzle flow then rains back onto the galactic plane at velocities in the range observed in intermediate and high velocity HI clouds .

Conclusions : We study a nozzle flow driven by a wind from a SSC close to the Galactic centre .
We find that for velocities within the range expected for a SSC wind , we can produce nozzle flows that stall above the galactic plane .
These stalled flows produce cool , infalling clouds with velocities similar to those of intermediate and high velocity HI clouds .