Each of the sections is separated by {TAIL ~ a retainer ring} having {HEAD ~ an opening} therein smaller in area than the area of the next preceeding scrubber chamber 
Each of the sections is separated by { TAIL ~ a retainer ring } having { HEAD ~ an opening } therein smaller in area than the area of the next preceeding scrubber chamber
OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH