In a spinning device of an open end spinning machine, a silver is fed to and passes through a feeding and opening device which opens the silver into individual fibers and feeds them into a rotary spinning chamber where they are collected and discharged as a finished yarn therefrom. In order to clean the fibers, when they pass through the feeding and opening device, dirt of the fibers is adapted to be thrown out by centrifugal force and leaves the fibers through a dirt discharge opening and enters through an intermediate duct into a dirt collecting chamber. The chamber is provided with an air inlet opening into the atmosphere and an air outlet connected with a source of negative pressure to produce a current of air which flows through the air inlet and outlet and by which the dirt collected in the chamber is continuously removed out of the chamber. A part of the air current tends to be directed through the intermediate duct to the dirt discharge opening. However, the intermediate duct has a portion with a cross-sectional area sufficiently smaller than that of the dirt collecting chamber so that the speed of that part of the air current becomes smaller than a terminal speed of the dirt.