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