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