Abstract: An air sifting apparatus for dry preparation of material comprising an apertured sifted material carrier for receiving material from a material feed device. An air plenum is disposed below the carrier and is comprised of two chambers that are separated from one another and are disposed one after the other in the direction in which the material is conveyed by the carrier. Each chamber has an air inlet for receiving a constant partial air stream. Respective inlet conduits deliver a pulsating air stream to each chamber. The air plenum supplies an air stream that flows through the carrier to loosen and layer the material received thereby into a heavy material layer and a light material layer disposed on the heavy material layer. The air stream is composed of the constant partial air stream and the pulsating air stream.

Abstract: A rotary piston valve arrangement, for a pneumatic settling tank, including rotary piston valves disposed in a common housing, with a first rotary piston valve being designed for the control of an additive stroke, and a second rotary piston valve being designed for the control of a discharge position. To reduce the amount of air required for controlling the settling tank, an element is provided for periodically shutting off the passage of air between the air inlet opening of the first rotary piston valve and the settling chamber during the time interval of an intake position of the first rotary piston valve and a simultaneous discharge position of the second rotary piston valve.