{HEAD ~ An irrigation system} contains {TAIL ~ a safety relief valve} and a safety relief valve control valve 
contains
{ HEAD ~ An irrigation system } contains { TAIL ~ a safety relief valve } and a safety relief valve control valve
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH