Many applications want to minimize air leaking into or out of the process. Whether this is for operational reasons or for economic reasons often depend on the process and the operator. Some applications outside air could humidity in the air to plug up filters/ hopper. Other times the atmosphere inside is dangerous and leaking outside before treatment could cause issues.
When you have these applications, the rotary valve might not be the best airlock for you. Rotary valves have a clearance between the rotor and the housing so that the rotor can rotate without any interference. However, this clearance allows a free passage for airflow between the higher pressure atmosphere to the lower one. And the greater the differential the greater the flow rate will be.
Aerodyne offers a few special airlocks for these applications. Our Vacu-Valve is a low cost, low leakage valve for vacuum applications. While the double dump valve design minimizes air leakage while letting larger particles out. And finally, the Aerodyne R-valve is a rotary valve with rubber wipers that minimize air leakage past the rotor.