Anyone using a rotary valve on abrasive material knows wear issues are a given.  Closed end rotors with compressed air injected between the rotor and endplate is an industry accepted method of combating this problem and extending the life of rotary airlocks.  Back in the good old days when 3 and 4-inch conveying systems were the "norm", 20-30 SCFM of compressed air was an acceptable "cost" of purging these 7, 9, and 10" airlocks.  With today's systems getting bigger and bigger, the amount of compressed air required to purge the larger airlocks can be as much as 100 CFM of 90 PSIG air.  The problem is 100 CFM of compressed air very expensive and rarely does anybody have 100 CFM of air to "give" to this application. Smoot has solved this problem with the exclusive  "Cavity Air Purge" system that actually uses air from the blower package in place of compressed air to do this job.