Spinneret

A spinneret for producing hollow fiber membranes, comprising two nozzles, wherein each nozzle comprises an outer ring slit and a central orifice,

• wherein the outer ring slits of the two nozzles are in fluid communication with a compartment for a polymer solution,
• wherein the spinneret comprises a spinneret body and two nozzle inserts having identical dimensions and each comprising a capillary, a reservoir for a center fluid, and a feed port for a center fluid,
• wherein the spinneret comprises a single feed port for a polymer solution located in a side wall of the spinneret and connected to the compartment for a polymer solution, characterized in that the feed port for the polymer solution is connected to the compartment defined by the inner wall of the spinneret body and the outer surface of the nozzle inserts,
• wherein the compartment comprises a first rotationally-symmetrical shell formed around a first nozzle insert, a second rotationally-symmetrical shell formed around a second nozzle insert, and a tubular duct connecting the first rotationally-symmetrical shell and the second rotationally-symmetrical shell aligned with the orifice of the feed port for the polymer solution and having the same inner diameter as the feed port for the polymer solution,
• wherein each capillary is connected to a separate reservoir for the center fluid not in fluid communication with the other reservoirs and which in turn is connected to a separate feed port for the center fluid.