A method for the production of polyamide 6 pellets, comprising the steps of a) providing a melt of polyamide 6; b) feeding the melt into an underwater pelletizing system being operated with a fluid and producing pellets from the melt; c) transporting the pellets from the underwater pelletizing system with the fluid into an upper side of a vertical vessel having a cylindrical section and a tapered bottom section connected to a pipe comprising a screw and / or a rotary gate valve for conveying the pellets; d) extraction of cyclic dimers and oligomers from the pellets; wherein - step d) takes place in the underwater pelletizing system, - after sedimentation by gravity into the tapered bottom section of the vertical vessel, the pellets together with residual amounts of the fluid are conveyed by the screw and / or the rotary gate valve through the pipe from the vertical vessel; - the fluid in the underwater pelletizing system and the vertical vessel comprises an aqueous solution of ε-caprolactam, - the fluid in the underwater pelletizing system is held at a temperature between T g + x · (T m - T g) and y · T m, wherein T g and T m are the glass transition temperature and the melting temperature of the polyamide 6, with x = 0.5 to 0.8 and y = 0.95 to 1.0, - the tapered bottom section of the vertical vessel is cooled, - a pressure between 4 bar and 12 bar is maintained in the underwater pelletizing system and the vertical vessel, and - the fluid is circulated between the underwater pelletizing system and the vertical vessel wherein a fraction thereof is withdrawn from circulation and the residual amounts of fluid leaving the vertical vessel with the pellets via the pipe and the withdrawn fraction are replenished with fresh fluid. a) providing a melt of polyamide 6; b) feeding the melt into an underwater pelletizing system being operated with a fluid and producing pellets from the melt; c) transporting the pellets from the underwater pelletizing system with the fluid into an upper side of a vertical vessel having a cylindrical section and a tapered bottom section connected to a pipe comprising a screw and / or a rotary gate valve for conveying the pellets; d) extraction of cyclic dimers and oligomers from the pellets; - step d) takes place in the underwater pelletizing system, - after sedimentation by gravity into the tapered bottom section of the vertical vessel, the pellets together with residual amounts of the fluid are conveyed by the screw and / or the rotary gate valve through the pipe from the vertical vessel; - the fluid in the underwater pelletizing system and the vertical vessel comprises an aqueous solution of ε-caprolactam, - the fluid in the underwater pelletizing system is held at a temperature between T g + x · (T m - T g) and y · T m, wherein T g and T m are the glass transition temperature and the melting temperature of the polyamide 6, with x = 0.5 to 0.8 and y = 0.95 to 1.0, - the tapered bottom section of the vertical vessel is cooled, - a pressure between 4 bar and 12 bar is maintained in the underwater pelletizing system and the vertical vessel, and - the fluid is circulated between the underwater pelletizing system and the vertical vessel wherein a fraction thereof is withdrawn from circulation and the residual amounts of fluid leaving the vertical vessel with the pellets via the pipe and the withdrawn fraction are replenished with fresh fluid.