{HEAD ~ The width} of the valve member is smaller than {TAIL ~ a peripheral dimension} of the openings 
is smaller than
{ HEAD ~ The width } of the valve member is smaller than { TAIL ~ a peripheral dimension } of the openings
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH