Operability Design Considerations
Automatic draft control dampers must open on failure of the damper control signal or power source. Backup manual damper operators should be provided so that one person can, without excessive effort, position the damper blade in any desired position from grade.
The dynamic behavior of the forced/induced draft system used with air preheat must be thoroughly analyzed. The combination of excess fan capacity and fail-open damper control can create a surge of air to the burners. In one installation, this occurred just as burners were cut back to minimum firing. A slow acting bypass fuel pressure controller allowed burners to be blown out.