| 摘要 |
PURPOSE:To prevent worsening or an air-fuel ratio, by a method wherein, even when a gas valve for switching is situated on the downstream side of a gas pressure control type proportional valve, unbalance occurring to the nozzle pressure of a burner is prevented from increasing. CONSTITUTION:A partition 7, having a small opening part, incurring a pressure loss higher than that of a switching gas valve and the like, is formed in a gas passage extending to a first burner group 5 not through a switching gas valve 4. When the first burner group 5 and a second burner group 6 simultaneously perform combustion, a combustion amount of the first burner group is set to a value lower than that of the second burner group. Thereby, when, with the switching gas valve 4 closed, only the first burner group 5 effects combustion, a pressure loss of the passage on the secondary side of a proportional valve is decreased with the decrease in a total flow rate. The small opening part of the partition wall is set so that, when a nozzle pressure is increased, the nozzle pressure of the first burner group is increased over that of the second burner group. This constitution prevents large disturbance of an air-fuel ratio occasioned by opening and closing of the switching gas valve, and provides stable combustion. |
