CleaverBrooks CBEX-DE, Эксплуатация и обслуживание

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750-392
CBEX-DE
3-3
Burner Operating Controls: General
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.
On a hot water boiler, the high limit temperature control should be 5º F to 10º F above the operating limit
temperature control setting. The setting should be sufficiently above the operating limit temperature to avoid
unnecessary shutdowns. On a 30 psig hot water boiler, the setting is not to exceed 240º F. The control
requires manual resetting after tripping on a temperature increase. To reset, allow the water temperature to
drop below the cutout setting less the differential, and then press the manual reset button. Failure to do this
will disallow restarting.
When adjusting or setting controls, first be sure all control devices are securely mounted and level. With the tem-
perature sensing control, make sure the sensing bulb is properly bottomed in its well and is secured against
movement. Be sure the connecting tubing is not kinked.
The dial settings are generally accurate, although it is not unusual to have a slight variation between a scale set-
ting and an actual pressure gauge or thermometer reading. Always adjust control settings to agree with pressure
gauge or thermometer readings. Accurate instrument readings are required. When necessary use auxiliary test
equipment to set controls.
Burner controls correctly set to match load demands will provide operational advantages and achieve the follow-
ing desirable objectives:
•
The burner will be operating in low-fire position prior to shutdown.
•
The burner will operate at low-fire for a brief period on each start during normal operation.
•
Eliminates frequent burner on-off cycling.
The Hawk control system modulates the boiler firing rate according to stored combustion curves. The firing graph
in Figure 3-1 depicts a typical interrelation of the operating limit control, modulated firing, and the high limit con-
trol.
The burner will be “on” whenever the pressure or temperature is less than point B and “off” whenever pressure or
temperature is greater than point A . The distance between points A and B represents the “on-off” differential of
the operating limit control.