a pair of flow systems, {HEAD ~ each said flow system} being disposed for a flow of {TAIL ~ fluid} there through 
a pair of flow systems , { HEAD ~ each said flow system } being disposed for a flow of { TAIL ~ fluid } there through
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH