Do not use 'Control': (Control is for switch logic, such as if reservoir full then turn the pump off.)
use a 'Valve' as a link between two nodes
set type to 'PRV' (there are also psv, pbv, fcv, tcv and gpv.)
put setting at 75, also set downstrean node elevations correctly.
the program will set the pressure at 75 and adjust flow until the equations balance. If there is not enough pressure upstream to provide the needed flow there will be an error.
Hydrae