Premixing apparatus

Abstract

A premixing apparatus for mixing air with a fuel gas in order to supply a burner with an air-fuel mixture through a fan, wherein a downstream end of a gas supply passage is connected to a gas suction part disposed in a portion, on an upstream side of the fan, of an air supply passage. The gas supply passage has interposed therein a zero governor for adjusting a secondary gas pressure to an atmospheric pressure. Even if the calorific value of the fuel gas may fluctuate, excess air ratio of the air-fuel mixture is arranged to be maintained at a constant value. The premixing apparatus is provided with: an excess air ratio detection device for detecting an excess air ratio of the air-fuel mixture; and a flow control valve interposed in a portion, on a downstream side of the zero governor, of the gas supply passage. The flow control valve is controlled such that the excess air ratio of the air-fuel mixture detected by the excess air ratio detection device becomes constant.

1 . A premixing apparatus for mixing air with a fuel gas in order to supply a burner with an air-fuel mixture through a fan, wherein a downstream end of a gas supply passage is connected to a gas suction part disposed in a portion, on an upstream side of the fan, of an air supply passage, the gas supply passage having interposed therein a zero governor for adjusting a secondary gas pressure to an atmospheric pressure,
 the premixing apparatus comprising:   an excess air ratio detection device for detecting an excess air ratio of the air-fuel mixture; and   a flow control valve interposed in a portion, on a downstream side of the zero governor, of the gas supply passage,   wherein the flow control valve is controlled such that the excess air ratio of the air-fuel mixture detected by the excess air ratio detection device becomes constant.   
     
     
         2 . The premixing apparatus according to  claim 1 , further comprising:
 a swing valve provided in an air-fuel mixture supply passage between the burner and the fan, the swing valve being capable of swinging from a closed posture of being hung down with an upper end shaft serving as a fulcrum to a bottom-up open side against a self-weight thereof.   
     
     
         3 . The premixing apparatus according to  claim 1 , further comprising:
 a bypass passage having interposed therein an on-off valve, the bypass passage being disposed in parallel with the flow control valve and in a portion, on the downstream side of the zero governor, of the gas supply passage.   
     
     
         4 . The premixing apparatus according to  claim 2 , further comprising:
 a bypass passage having interposed therein an on-off valve, the bypass passage being disposed in parallel with the flow control valve and in a portion, on the downstream side of the zero governor, of the gas supply passage.