Which companies make large diameter (eg 500 mm) flow control valves  for water transmission mains, which can be driven by an electric actuator ?

You may need to be more specific as to valve type.  As far as I know, most of the valves of that size and larger can be equipped with electric actuators.  I would assume a Google search would turn up some names right quick.  And call some valve suppliers in your area and see what brands they furnish.

TO BE EXACT I am looking for a globe valve, or ported piston valve, or axial flow (needle) valve, or an eccentric plug valve - i.e. something with good controllability - not a gate valve or a butterfly valve !!!

you can see the GA valves, Golden Anderson Valves, globe type, piston and V ports.

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