There are a number of different names used to refer to rotary valves – rotary feeders or rotary airlocks. These names technically refer to a similar mechanical device with regards to its design and appearance. The valve can function as a combination of the two (feeder and airlock), hence, the name airlock feeder. During operation, the bulk material goes in through the valve's inlet and is transported across its housing surface to the outlet by means of the rotor pockets as the rotor shaft rotates. There are two types of rotations, namely, the load side rotation and the return side rotation. The former is considered to be the rotation of the vanes and the pockets from the entry point to the exit point, while the latter is the rotation of the vanes and the pockets from the outlet to the inlet. The valve can precisely discharge and feed powder or granular bulk materials from hoppers or silos. A rotary valve can operate as a rotary airlock feeder in situations where pressure differentials are present, situations such as pneumatic operating lines. This implies that the airlock feeder can allow material flow while reducing air leakages. Its blades form a slight seal against the housing surface; hence, reducing air leakages.