In this paper we consider theoretically study of many pocket stone catcher. The quality of cotton fiber depends on primary qualitative processing of raw cotton. One of the operations of cotton processing consists of cleaning cotton from various impurities such as small and large things like a heavy stone. Such extraneous things must be removed before ginning process. To separate the heavy things of cotton, stone catchers are needed, that is installed between separator and cotton gin. Constructions of stone catchers are in different form such as cylindrical, rectangular in pipe bends. Cotton from bale transported by air at high speed through pipelines with a diameter of 0.2 - 0.3 Air speed is 15-20 m / s. In the rotary section of the pipeline installed stone catchers. Due to centrifugal forces of inertia, heavy impurities separated from the cotton move to the working chamber and stone catcher. There is need to examine the trajectory of cotton and heavy impurities in order to install the pocket
Based on these considerations viewed the probability approach to the stone catcher: determined the effect of catching depending on the geometric dimension of stones, studied movement of cotton and heavy impurities at the entrance of the separation chamber.
Equations of motion such as character movement, trajectory of cotton and heavy impurities are obtained with the help of principle of d'Alembert. According to the theory of motion of heavy impurities and raw cotton, found the optimal location of the pockets at the bottom of impurity.