Thus, the check valve is between {HEAD ~ the furnace} and {TAIL ~ components} 4 8 in the feed line 
Thus , the check valve is between { HEAD ~ the furnace } and { TAIL ~ components } 4 8 in the feed line
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH