{HEAD ~ A flow switch} 70 detects {TAIL ~ the movement} of liquid through the shell 12 by testing for flow in the shell liquid outlet tube 56 and prevents the burner 16 from firing when there is no flow 
detects
{ HEAD ~ A flow switch } 70 detects { TAIL ~ the movement } of liquid through the shell 12 by testing for flow in the shell liquid outlet tube 56 and prevents the burner 16 from firing when there is no flow
HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL 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 OTH OTH OTH