Negative pressure in the heating furnace
Thread Content
During the most recent chain shutdown of the heating furnace, why did the negative pressure inside the furnace increase at the moment the flame detection system stopped detecting a flame, and only afterward did positive pressure occur?
Logically, in the case of a shutdown sequence for a heating furnace, fuel supply should be stopped. For furnaces with natural ventilation, it’s sufficient to fully open the flue dampers. In the case of furnaces with forced ventilation, fuel supply and the blower fans need to be stopped first, after which the flue dampers should be fully opened along with the fast-opening air valves. In your situation, the negative pressure inside the furnace increases; so shouldn’t the fast-opening air valves be opened later, after the flue dampers have been fully opened? Could not keep up with the speed of movement of the flue baffle? But how is it that no positive pressure should form later on? I don’t understand; I hope some expert can clarify this as soon as possible!
In the case of interlocked shutdown of a forced-air heating furnace, when no other operations are carried out, the negative pressure increases; the fuel gas supply is cut off, and since the exhaust fans do not shut down automatically, the suction force becomes even greater.