| 摘要 |
<p>PROBLEM TO BE SOLVED: To provide a premixing device comprising: air resistance switching means switching a ventilation resistance of an air supply path 3 between high and low with a downstream end of a gas supply path 4, on which a flow volume regulation valve 6 disposed, connected to the air supply path 3 upstream of a fan 2; and gas resistance switching means switching a ventilation resistance of the gas supply path 4 between high and low, and capable of preventing occurrence of combustion failure when the air resistance switching means and the gas resistance switching means switch the ventilation resistances to higher resistances.SOLUTION: Air resistance switching means is constituted by a butterfly valve 7 provided rotatably in an air supply path 3. Gas resistance switching means includes a valve element 82 in a valve casing 81 partitioned from the air supply path 3, and is constituted by a switching valve 8 switching a ventilation resistance between high and low in response to approach/separation of the valve element 82 to/from a valve seat 83 within the valve casing 81. If the butterfly valve 7 is rotated in a direction of increasing the ventilation resistance, then a part of the butterfly valve 7 abuts on an operation rod 84, and the valve element 82 is pressed and moved in a direction of approaching the valve seat 83 via the operation rod 84.</p> |
