Sheet 4343-3 Page 2
TWINBED ® II FIRING/FLAME SCANNING SEQUENCE Conventional Firing (main flame in the tile) Stop Cycle Stop Cycle (low fire) (low fire)
Burner(s)
LNI Firing (furnace above 1450 F [788 C])
Burner "A" Main Scanner Main Flame Pilot Flame Rod
Off on off on off
on off
on off
on
on
Pilot Flame
on.............loss of pilot flame will result in a shutdown of all burner fuel
time
time
Burner "B" Main Scanner Main Flame Pilot Flame Rod
on off on
on off
on off
on
on
on.............loss of pilot flame will result in a shutdown of all burner fuel
Pilot Flame
off (pre-start
(pilots only)
"A" "B" "A" "B" fires fires fires fires
transitions
"A" "B" "A"
"B"
check)
to and
fires fires fires fires
from LNI
note 1
note 2
note 3
note 4
The above diagram shows the relationship between the flame detectors and introduction of main fuel. Each TwinBed II burner uses a flame rod to monitor the pilot flame and a flame scanner to monitor the main flame. The main flame scanner mounting is such that it can not "see" the pilot flame.
Flame Scanners:
Flame scanners other than Fireye UV7A4 and Fireye UV1AL may require different adapters than listed. Contact North American for information. Page 3 lists scanner assembly details, item 16. For burners controlled by systems other than a North American Safety PLC, a self-check- ing scanner must be used on the main flame.
NOTES:
1. Prior to the pilots being ignited, both the pilot and main flame scan- ners are "switched" on (electrically connected to the flame controller) so the flame controller can perform a diagnostic check of both scan- ners.
Pressure Reference Lines
Pressure reference lines (lines with hash marks) to regulator diaphragm chambers may be 3 / 8 " or ½ " stainless steel or copper tubing. Do not use steel tubing which will rust and may eventually block the passage.
2. In the "Stop Cycle" mode, all air, exhaust, and fuel "cycle valves" are closed. The flame monitoring is of the pilot flame only.
Pilot Location
3. When the burners are firing "conventionally", with main fuel being introduced through the "burner fuel" connection, the pilot flame rod is "switched" off. In this "state", the flame monitoring system will be maintained by the main scanner "seeing" the main flame even though the pilot is still burning. The "exhausting" burners flame monitoring system is maintained by detection of its pilot flame. 4. When the burners are firing in the "injector mode" (LNI), the flame monitoring system is maintained by the pilot flame rod in both the firing and exhausting burners. The primary safety limit for the intro- duction of main fuel, in addition to all other required limits, is proving the furnace and by-pass flue are above "auto ignition" temperature.
The TwinBed in the schematic has the pilot located on the left side and main UV on the right (4343-BL1). Locations of pilot and main UV can be reversed (4343-BR1). Typical Pilot Adjustments
CAUTION! Standards-compliant functioning of the Flame Detection System can be compromised if the pilot system is not configured and adjusted strictly in accordance with the information outlined in Sheet 4343-3.
Set pilot with zero main burner air pressure.
Pilot Gases
Nat. Gas
Air
Adjust Item
#12
#3
INFORMATION ON PAGE 1 SCHEMATIC
4020-3A-CB Flow (scfh) 4020-3-CB Flow (scfh) 4020-4-CB Flow (scfh)
30 47 70
232 360 540
Air Pressure Regulation
Pressure (P)
4.3"w.c.
4.3"w.c.
Because of the wide swings in backpressure that occur when TwinBed II cycles between firing and exhausting, a regulator (item 1) is used to maintain constant pressure drop across the pilot and fuel tube cooling passage. Constant pressure drop translates into constant flow.
Measure P. at Item
#13 (pilot gas)
#4 (pilot air)
Pilot operation is best when slightly fuel rich as in above air flows.
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