  We study the effects of radial flows on Galactic chemical evolution. A simple
analytic scheme is developed prescribing the coupling of infall from the
intergalactic medium and radial flows within the disc based on angular momentum
conservation. We show that model parameters are tightly constrained by the
observed [Fe/H]-abundance gradient in the Galactic disc. By this comparison the
average rotational velocity of the onfalling material can be constrained to 0.7
< v/V_c < 0.75, or respectively ~ 160 km/s when assuming a constant disc
circular velocity of V_c = 220 km/s. We test the robustness of this value
against the influence of other processes. For a very simple model of inside-out
formation this value changes only by \Delta v/V_c ~ 0.1, i.e. ~ 20 km/s, and
significantly less on more realistic scenarios, showing that inside-out
formation does not alone explain the abundance gradient. Effects of other
uncertain parameters, e.g. star formation history and star formation efficiency
have very small impact.
  Other drivers of inflow beyond our explicit modelling are assessed by adding
a fixed inflow across the whole disc. The churning amplitude only mildly
affects the results mostly by slightly flattening the metallicity gradient in
the inner disc. A new process causing radial gas flows due to the ejection of
material by stars moving on non-circular orbits is studied and seems to
contribute negligibly to the total flows. We further show that gaseous outer
discs cannot be the main source feeding the persistent star formation in the
inner regions by a direct inflow.
