Preparations for Startup
3-2
750-392
CBEX-DE
Prior to startup the boiler should be filled to the proper operating level with water at ambient temperature. Be
sure that treated feedwater is available. In heating applications, the entire system should be filled and vented.
On a steam boiler, open the vent valve to vent air displaced during filling. Leave the test valve open until steam
is noted after the burner is operating.
Check for rotation of all motors by momentarily closing the motor starter or relay. Correct rotation is normally
labeled in a readily visible location near the motor housing.
Contact the local Cleaver-Brooks authorized representative or the Cleaver-Brooks Service Department for recom-
mendations covering special controls that are not included in this chapter.
3.2 — Burner Operating Controls: General
The term ‘controls’ as used in this manual can refer to:
• The Operating Limit and High Limit controls, hardware devices which turn the boiler on and off according to
their respective switch settings.
• The Modulating and Flame Safeguard controls, which provide for modulated firing and burner sequencing/
flame supervision. On a standard CBEX Elite these functions are managed by the Hawk integrated control sys-
tem, comprising both hardware (PLC, Input/Output devices, and touchscreen HMI) and software (program-
ming for the PLC and HMI).
The limit controls are described below; for a complete description of the Hawk including adjustment procedures,
see the manual provided with the boiler control system.
1. Operating Limit Control: Senses pressure or temperature and automatically turns the burner on to initiate the
startup sequence when required and turns the burner off to initiate the shutdown sequence when the demand
is satisfied. The control must be set to initiate startup only at the low-fire position.
The operating pressure control of a steam boiler should be set slightly above the highest desired steam pres-
sure, but at least 10% lower than the setting of the safety valve. Set the “cut-out” (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 temperature operating control on a hot water boiler should be set slightly above the highest desired water
temperature and within the limits of the pressure vessel. The “cut-in” (burner on) temperature is the cutout
temperature minus the differential.
1. High Limit Control: Senses the steam pressure or hot water temperature. It is used as a safety limit to turn
the burner off in the event the operating limit control fails. The high limit control should be set sufficiently
above the operating limit control to avoid nuisance shutdowns, because it has a manual reset feature
On a high pressure steam boiler, the high limit control should be set approximately 10 psig above the operat-
ing limit pressure control setting, if feasible, or midway between the operating limit pressure and the safety
valve setting.
NOTE: Adjustments to the boiler operating controls should be made by a qualified Cleaver-Brooks Service Techni-
cian. Refer to the appropriate C-B Hawk manual for information on the Hawk control system.
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