Three-pass boiler

摘要

The invention relates to a three-pass boiler, comprising a water-conducting housing (1) having a combustion chamber (3) forming the first pass (2), with discharge openings (5) which are remote from the burner and lead to the second pass (4) which is separated into ducts (4') and extends along the combustion chamber (3), to which second pass (4), which is closed to the waste gas collecting chamber (7), the third pass (6), which is likewise separated into ducts (6') and likewise extends along the combustion chamber (3), extends in parallel. In order in a simple way to adapt the available throughflow volume of the passes to the decreasing waste-gas volume, according to the invention the ducts (4') forming the second pass (4) have, in total, a larger throughflow volume than that of the third pass (6), the larger number of ducts (4') of the second pass (4) being arranged below the horizontal longitudinal median plane (E) of the combustion chamber (3) and a smaller number of said ducts (4') being arranged together with all the ducts (6') of the third pass (6) being arranged above the horizontal longitudinal median plane (E) of the combustion chamber (3), and furthermore the combustion chamber (3) being closed to the burner side by an annular screen (11). <IMAGE>