Security sieve for sifting out foreign materials, dissolving of product lumps and fluidizing the product in pressure-tight operation, respectively pneumatic conveying systems. Safety screens can also be used for bag emptying stations to reduce the risk of contamination by pieces of paper, string, and other contaminants from the bagged material. Rotary sieves allow precision sieving down to 400 µm. The material is fed into the body of the screen and conveyed by a screw to a perforated pre-screen for the protection of the filter. A motor drives the shaft with the feeding screw and the beater shaft. The beaters circulate the product gently through the mesh. Coarse material is discharged via a separate tailings container and the product sifted is transported to a collecting cone where it can be further handled. The design of the rotary screens allows quick, tool-free removal of the filter and rotating shaft for inspection and cleaning. The opening of the door is secured by position switches for unexpected start of the sieve. The bearings are sealed by double bearings with compressed air bleeding. Delivered complete with ground support, tailings container, inspection hatch.