Startup and Operation
4-14
750-392
CBEX-DE
4. The combustion air pressure or atomizing air pressure drops below minimum level.
When the burner is shut down normally, by either the operating limit control or by manually switching the burner
off, the load demand light will turn off.
Shutdown through flame failure will actuate the flame failure light (and alarm, if so equipped) and the load
demand light will remain lit. The cause of this type of shutdown will have to be located, investigated, and cor-
rected before operation can be resumed.
4.9.2 — Shutdown
When the operating limit control setting is reached to open the circuit or if the burner switch is turned “off,” the
following sequence occurs:
1. The fuel valve is de-energized and the flame is extinguished.
2. The timer begins operation and the blower motor continues running to force air through the furnace in the
post-purge period.
3. At the end of the programmed post-purge period, the blower motor is turned off. The air pump motor of an oil
fired burner is also turned off.
4. The timer has returned to its original starting position and stops. The unit is ready to restart.
4.10 — Control Operational Checks
Proper operation of the various controls should be verified and tested when the boiler is initially placed into ser-
vice, or whenever a control is replaced. Periodic checks should be made thereafter in accordance with a planned
maintenance program.
The operating limit control may be checked by allowing steam pressure or water temperature to increase until
the burner shuts down. Depending upon the load, it may be necessary to manually increase the firing rate to
raise steam pressure to the burner shutoff point. If the load is light, the header valve can be closed or throttled
until the pressure increases. Observe the steam gauge to check the cutoff pressure as the operating limit control
shuts the burner down. Slowly open the header valve to release steam pressure and check the cut-in setting as
the burner restarts. Check the modulating control for the desired operating pressure range.
The water temperature on a hot water boiler that may be operating at less than full load may be raised by man-
ually increasing the firing rate until the burner shuts down through the action of the operating limit control.
Observe the thermometer to verify the desired settings at the point of cutout and again when the burner restarts.
Return the manual-automatic switch to “automatic” and check the modulating control for the desired tempera-
ture range.
Check the proper operation and setting of the low-water cutoff (and pump operating control, if used). For C-B
Level Master, see manual 750-281.
NOTE: There can be other reasons for shutdown such as motor overload, flame outage, tripped circuit breakers,
blown fuses, or through other interlock devices in the circuitry.
To Next Page
Loading...
Need help?
General
