{HEAD ~ An exhaust line} 11 is connected to {TAIL ~ the feed line} between check valve 10 and the furnace and includes two power controlled shut off valves 20 and 21 between the furnace and the exhaust line outlet 
is connected to
{ HEAD ~ An exhaust line } 11 is connected to { TAIL ~ the feed line } between check valve 10 and the furnace and includes two power controlled shut off valves 20 and 21 between the furnace and the exhaust line outlet
HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH