Adjustment Procedures
6-4
750-368
CBEX Elite 100-1200 HP
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.
6.3 — Operating Limit Pressure Control
Set the “cutout” (burner off) pressure on the range scale using the large adjusting screw. The “cut-in” (burner on)
pressure is the cutout pressure minus the (fixed) differential. The cutout pressure should not exceed 90% of the
safety valve setting.
6.4 — High Limit Pressure Control
The high limit control provides a safety factor to shut the burner off in the event the operating limit control should
fail.
Set “cutout” (burner off) pressure on the main scale using the adjusting screw. The control will break a circuit
when pressure reaches this point. The setting should be sufficiently above the operating limit pressure control to
avoid nuisance shutdowns, and preferably not exceed 90% of safety valve setting.
The control requires manual resetting after tripping on a pressure increase. To reset, allow pressure to return to
normal and then press the reset button. Failure to do this will disallow restarting.
In the setting of the controls, consideration must be given to the time required for a burner restart. Each start
requires a pre-purge period, plus the fixed time required for proving the pilot and main flame. In addition,
approximately one-half minute is required for the damper actuator to travel from low- to high-fire. The time lag
may allow pressure or temperature to drop below desirable limits.
NOTE: On-off cycling in excess of 8 cycles per hour will shorten the life of the combustion air motor and cause exces-
sive 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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