750-392
CBEX-DE
3-5
Control Checks
Do not operate the boiler in excess of 90% of the safety valve relief setting. The closer the operating pressure is
to the safety valve relief pressure, the greater the possibility of valve leakage. Continued leakage, however slight,
will cause erosion and necessitate early safety valve replacement. The control settings on a hot water boiler must
be within the temperature limits of the boiler.
Ideally, the boiler operating controls should be set under actual load conditions. Especially under new construc-
tion conditions, the boiler is initially started and set to operate under less than full load requirements. As soon as
possible thereafter, the controls should be reset to provide maximum utilization of the modulating firing system.
To accomplish maximum utilization, and assuming that air/fuel combustion ratios have been set, make the
required adjustments to the controls to bring the boiler pressure or temperature up to meet the load require-
ments.
Modulation settings should be adjusted under load conditions, until the load is maintained with the burner firing
at a steady rate. The firing rate at that point may be full high-fire or slightly less, depending upon the relationship
of the boiler size to the load.
3.3 — Control 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. See chapter 6 for instruc-
tions on the adjustment of controls.
Check the proper operation and setting of the low-water cutoff (and pump operating control, if used).
Proper operation of the flame failure device should be checked at startup and at least once a week thereafter.
Check the program relay’s annunciation for any system failure. Observe the promptness of ignition of the pilot
flame and the main flame.
NOTE: Frequent on-off cycling will shorten the life of the combustion air motor and cause excessive wear on switch
gear and pilot electrodes. It also substantially reduces fuel efficiency.
NOTE: It is not recommended that the boiler controls be set so as to overlap the modulation range and operating
control range.
NOTE: Rapid heat input can subject the pressure vessel metal and refractory to premature failure.
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