{HEAD ~ Reverse thermosiphoning} under {TAIL ~ normal conditions} is prevented by a ball type check valve 
under
{ HEAD ~ Reverse thermosiphoning } under { TAIL ~ normal conditions } is prevented by a ball type check valve
HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH