A flexible diaphragm situated in a rigid shell affixed over an opening in the element wall divides {HEAD ~ the shell interior} into {TAIL ~ first and second variable volume chambers} 
into
A flexible diaphragm situated in a rigid shell affixed over an opening in the element wall divides { HEAD ~ the shell interior } into { TAIL ~ first and second variable volume chambers }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL