Premixing apparatus, heat source apparatus, and water heater

Abstract

A premixing apparatus includes a mixing unit, an air supply adjusting unit, and a gas switching unit. The mixing unit draws a fuel gas in the mixing unit by supplied air to mix the fuel gas and the supplied air with each other. The air supply adjusting unit applies a load on the supplied air flowing toward the mixing unit and switches the load. The gas switching unit switches a gas amount of the fuel gas to be supplied to the mixing unit.

1 . A gas switching unit comprising:
 a gas switching block having a gas path including first, second and third paths;
 a first opening and closing valve disposed on the second path to open or close the second path; and 
 a second opening and closing valve disposed on the third path to open or close the third path, wherein 
 a path area of the gas path is changed stepwise by the first path and by the second and the third paths that are able to be opened and closed. 
   
     
     
         2 . The gas switching unit according to  claim 1 , further comprising a switching plate fixed to the gas switching block, the switching plate having first, second and third through holes communicating with the first, the second and the third paths respectively, wherein
 the first, the second and the third through holes have different opening areas from each other.   
     
     
         3 . The gas switching unit according to  claim 2 , wherein
 the opening areas of the first, the second and the third through holes are equal to or smaller than path areas of the first, the second and the third paths respectively,   the path area of the gas path is adjusted by the opening areas of the first, the second and the third through holes.   
     
     
         4 . The gas switching unit according to  claim 2 , wherein
 the opening area of the first through hole is smaller than the opening area of each of the second and the third through holes.   
     
     
         5 . The gas switching unit according to  claim 2 , further comprising a fixing screw fixing the switching plate to the gas switching block, wherein
 the switching plate is replaceable in accordance with a gas type.   
     
     
         6 . A premixing apparatus comprising:
 the gas switching unit according to  claim 1 ; and   a mixing unit configured to mix a fuel gas supplied from the gas switching unit with an air.   
     
     
         7 . A heat source apparatus comprising:
 the gas switching unit according to  claim 1 ; and   a control unit including a processor to cause the first and the second opening and closing valves to open or close.   
     
     
         8 . A water heater comprising:
 the gas switching unit according to  claim 1 ; and   a control unit including a processor to cause the first and the second opening and closing valves to open or close.