at least one drive unit for {HEAD ~ at least one shut off device} for {TAIL ~ at least one fluid pipe}; and, 
for
at least one drive unit for { HEAD ~ at least one shut off device } for { TAIL ~ at least one fluid pipe } ; and ,
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH