With (6) ea, chamber doors removed and with (6) ea. soft covers in place, the Kobelco air compressor duty cycle is 

270 seconds LOADED vs 18 seconds UNLOADED = 94% df.  

This isn't, necessarily, unexpected but I noticed that the load/unload thresholds don'tt appear to be dictated by the receiver tank's pressure.  I'll investigate tomorrow, but my recolection is that the compressor should load at a receiver tank pressure of  80psi and unload at 110 psi.  This wasn't happening while I was observing a few cycles this evening.  Instead, the unloading appeared to be based on elapsed time as opposed to receiver tank pressure.  

I surveyed the open chambers and all soft covers are on and in-chamber work seems done for the day, so I reduced the purge flow a bit.