  The internal velocity fields of planetary nebulae are studied with a
resolution of 5 km s$^{-1}$. We analyze deep echelle spectra from three nebulae
in the Bulge, the Sagittarius Dwarf and the SMC. No effects of metallicity is
seen, except possibly a slower onset of the fast wind from the central star.
Robust evidence is found for the existence of a high-velocity shock at the
inner edges of the nebulae. Such a shock is predicted in hydrodynamical models
but had not previously been observed. The shock gas is accelerated by the fast
wind from the central star. A similar shock at the outer edges traces the
expansion of the ionized shell into the ambient AGB wind. Evidence for
localized regions of high velocity is also found from lines of intermediate
excitation, for two of nebulae. We explore several possible interpretations:
(1) an embedded shock at intermediate radii, as predicted by hydrodynamic
models at the position of the outer edge of the swept-up inner shell; (2)
deviations form spherical symmetry, where in some directions the
intermediate-excitation lines extend into the region of the outer shock; (3) An
intermediate swept-up shell, as seen in some Galactic planetary nebulae. The
remaining nebula, with a [WC] star, shows strong turbulence. This may trace a
superposition of many embedded shock-lets. We suggest a relation to the
time-variable [WC] wind, giving a planetary nebula subjected to a multitude of
sound waves.
