Cleaver-Brooks CBW - Operating Control and Modulating Control Actions

CHAPTERS
ADJUSTMENT PROCEDURES
*FIXED DIFFERENTlAL-STEAM CONTROL
ADJ. CIFFEREM1AL-HOTWATER CONTROL
[FIGURE 5-3/ OPERATING CONTROL AND MODULATING CONTROL ACTIONS]
Although a gap is shown between B and C, these
points may well coincide
if required by load
conditions. When set
as shown, the burner will
be in a low fire position upon a restart and will
fire at that rate for a short period
of time before
falling
pressure or temperature requires an in-
crease in the fuing rate. From this illustration
it
can be seen that this desirable objective will not
be attained if setting C overlaps point B. In that
event, upon a restart, the burner would drive
to a
higher firing position immediately after the main
flame was proven, and the brief period
of low
heat input would not occur. Actual settings will,
of course, depend greatly upon load conditions,
which will affect the amount
of differential per-
mitted
to· the operating limit control and to the
gap,
if any, between B and C.
CHAPTER 5-6
CAUTION!
Setting operating controls in
such a way that the burner
drives to a higher firing position
Immediately upon restart can
create cycle stress to the pres-
sure
vessel and eventual pres-
sure vessel failure.
When fuing a cold boiler, the burner must be kept
under manual flame control until normal operat
..
ing pressure or temperature is approached. The
size
of the flame may be manually increased to
gradually build up pressure
or temperature. If the
burner
is not under manual control on a cold start,
it immediately will move to high fire as soon as
the program control releases the circuit that holds
750-150