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.
So what is Cavity Air Purge? This is when the required volume of air is tapped off the blower package (by use of a small orifice plate which guarantees the required pressure and volume will ALWAYS be correct no matter what the operating condition of the system) and injected into the endplates of the airlock at a pressure just slightly higher than what is under the airlock. Just like what the compressed air system does on a smaller valve, this air provides a zone of higher pressure between the endplate and seals, forcing the air leakage into the airlock rather than out of the airlock, which is the leading cause of airlock seal failure.
Recently we received a rotary valve that was sent back to us from a customer who had one of our railcar pull/push unloading systems for unloading pebble lime. The system had been running non-stop for the last year and a half and finally wore out enough that they wanted to send it back to us for evaluation. The valve was a standard Type II rotary with Cavity Air Purge.
Did it work? Upon inspection of the valve, it was found that the valve could return to service by simply supplying a new housing. The rotor and endplates were in perfectly good condition and could be used again in the new housing. As you can see in the pictures, the inside bore of the housing has deep grooves cut in it which was the ultimate failure of the valve and why it was pulled from service. But you can also see in the pictures that the magic marker writing of 17.9852 on the rotor endplate and the 18.0019 on the endplate that were written on the valve during initial assembly are still there as clear and clean as the day the valve was made. Undeniable proof of the effectiveness of the Smoot Cavity Air Purge System.
