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