In many pneumatic conveying systems, a rotary valve or rotary airlock is used to feed the dry bulk material from one system to another. The other function of a rotary airlock is to help prevent the transfer of air from the system below the valve into the system above or vice versa. This cannot always be accomplished. Air leakage is a consistent issue when dealing with rotary valves in a pneumatic conveying system. It does not matter if the system is positive pressure or a negative pressure system (vacuum). This article will explain the root cause of air leakage, the effects of air leakage in each type of system, and options to reduce air leakage across the rotary valve.