750-368
CBEX Elite 100-1200 HP
4-5
4.5 — Flame Loss Sequence
4.4.4 — Burner Shutdown: Post-Purge
The burner will fire until steam pressure or water temperature in excess of demand is generated. With modulated
firing, the actuators should return to their low fire positions before the operating limit control (OLC) opens. When
the limit control circuit is opened, the following sequence occurs:
The main fuel valve circuit is de-energized, causing the main fuel valve (MGV or OV) to close. The flame is extin-
guished. The control panel lights (LDL and FVL) are turned off. The blower motor continues to run to force air
through the boiler for the post-purge period.
The blower motor start circuit is de-energized at the end of the post-purge cycle and the shutdown cycle is com-
plete.
The program relay is now ready for subsequent recycling, and when steam pressure or water temperature drops
to close the contacts of the operating control, the burner again goes through its normal starting and operating
cycle.
4.5 — Flame Loss Sequence
The program relay will recycle automatically each time the operating control closes, or after a power failure. It
will lock out following a safety shutdown caused by failure to ignite the pilot or the main flame, or by loss of
flame. Lockout will also occur if flame or flame simulating condition occurs during the pre-purge period.
The control will prevent startup or ignition if limit circuit controls or fuel valve interlocks are open. The control will
lock out upon any abnormal condition affecting air supervisory controls wired in the running interlock circuit.
1. No pilot flame: The pilot flame must be ignited and proven within a 10-second period after the ignition cycle
begins. If not proven within this period, the main fuel valve circuit will not be powered and the fuel valve(s)
will not be energized. The ignition circuit is immediately de-energized and the pilot valve closes, the reset
switch lights and lockout occurs immediately. The blower motor will continue to operate.
The flame failure light and the alarm bell (optional) are energized 10 seconds later.
The blower motor will be de-energized. The lockout switch must be manually reset before operation can be
resumed.
2. Pilot but no main flame: When the pilot flame is proven, the main fuel valve circuit is energized. Depending
upon the length of the trial-for-ignition period, the pilot flame will be extinguished 10 or 15 seconds later. The
NOTE: Normal operation of the burner should be with the controls in the automatic mode and under the direction of
the modulating signal. The manual mode is provided for initial adjustment of the burner over the entire firing range.
When a shutdown occurs while operating in the manual mode at other than low fire, the damper will not be in a
closed position, thus allowing more air than desired to flow through the boiler. Excess air flow subjects the pressure
vessel metal and refractory to undesirable conditions.
The lockout switch must be manually reset following a safety shutdown. The cause for loss of flame or any unusual
condition should be investigated and corrected before attempting to restart. Failure to follow these instructions could
cause damage to the equipment.
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