When your dust collectors are having issues, one of the first places to look is the airlock valve.  Often times, dust is hygroscopic and when outside air leaks into the system, humidity follows.  This can cause the dust to absorb the humidity and become sticky or harden like cement.  This can lead to plugged filters, hoppers and damage to rotary valves.  While rotary valves are the industry standard airlock, they constantly allow air leakage.  A low leakage valve is required. Double dump valves however are very low leakage, since there is no direct connection to the outside atmosphere.  The valve always isolates the conditions above it from the conditions below it.  This minimizes air leakage, thereby minimizing humidity from affecting the dust.

So if you have a non-explosive application that is hygroscopic, look into a double dump (flap) valve.

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