The invention relates to a screening device and a method for screening powders. The device comprises a screening space comprising a first chamber and a second chamber, which chambers are arranged adjacent and have a common partition wall. The device comprises a screen which is placed obliquely or vertically in the screening device, wherein the screen forms at least a part of the common partition wall. The first chamber comprises a raw material inlet, a drive gas inlet, a float gas unit, and a residual particle outlet. The second chamber comprises a product material outlet and a rotatable blade, wherein the blade comprises nozzles which are configured for blowing gas against the screen. In addition, the invention relates to an assembly comprising a first and second screening device, wherein the product material outlet of a first screening device is connected to the raw material inlet of the second screening device.