Abstract: Synthetic resin extruder comprising a rotatable extrusion head surrounded by a hollow ring rigidly secured, the interior of the ring communicating with a controllable supply of air for the head, said ring having an outer sliding face, in which are provided a number of passages equally spaced apart and closed by non-return valves having a portion projecting out of the sliding face, said face co-operating with a spring-controlled stationary shoe with a depression being provided with an air supply and the bottom of the depression co-operating with the valves to urge these into the open position.