Second Editon, May 2017 - Rotary valves are widely used in the food processing industry for continuous discharging, metering and dosing of dry particulate materials from or into attached plant components. Such applications involve hygienic material handling and therefore only rotary valves of approved hygienic design should be used. This document describes the design and operational features of rotary valves that are of importance when rotary valves operate in a hygienic processing environment.