Abstract: This invention relates to centrifugal separators of the kind having sludge ports at the rotor periphery to be opened during operation and separate outlets for separated heavier liquid phase and separated lighter liquid phase. To reduce the losses of valuable lighter liquid phase during total discharge or partial discharge of the separator by opening the sludge ports, the centrifuge is provided with an overflow device connected to the heavy phase outlet, said overflow device having an inner annular overflow and also having a number of passages at a larger diameter than the inner overflow border. The passages are dimensioned to let through all heavier liquid phase in normal operation but not to let through an increased amount of heavier liquid phase fed to the separator just before opening the sludge ports for the purpose of displacing the interface between the heavier and the lighter liquid phase towards the rotor axis to a level that corresponds to said inner overflow border.