6 which preferably is shaped to discharge the yarn across the full width of screen 7 screen 7 is in the form of a flat circular band rotating about vertical axis z and forms the bottom of a chamber defined additionally by sidwalls 8 8 and by cover 9 in the drawing the cover 9 is shown broken away in the area where tube 5 passes through the cover so as to show the yarn striking screen 7 and forming a plug spaced from the point of impingement on screen 7 as steam is discharged through the screen and the yarn fills the chamber and piles up in a plug on the relatively slow moving screen as previously explained this plug is represented in fig1 by back and forth loops but it is to be understood that these are symbolic only and do not display the actual structure of the yarn plug cover 9 includes a stationary circular tongue not shown snugly fitting down between the moving walls 8 8 cover 9 contains an outlet 10 therein in the form of an open sector through which the yarn plug is released the steam entering the chamber is discharged through screen 7 and withdrawn by means not shown the yarn from outlet 10 is passed through a yarn guide 11 and over an assembly of tension.