Adjustment Procedures Chapter 5
750-177 5-5
settings and should not exceed 90% of the valve setting. The
control requires manual resetting after it shuts off the burner.
In the setting of the controls, consideration must be given to
the time required for a burner restart. Each start, requires a
prepurge period, plus the fixed time required for proving the
pilot and main flame. In addition, approximately one-half
minute is required for the damper motor to travel from low to
high fire. The time lag may allow pressure or temperature to
drop below desirable limits.
F. MODULATING PRESSURE
CONTROL (Steam)
Turn the adjusting screw until the indicator is opposite the
low point of the desired modulating range. Modulated firing
will range between the low point and a higher point equal to
the modulating range of the particular control. In 0-15 psi
controls the range is 1/2 psi.
!
DANGER
CAUTION
To prevent burner shutdown at other than
low-fire setting, adjust the modulating pres-
sure control to modulate to low fire BEFORE
the operating limit pressure control shuts
off the burner. Failure to follow these in-
structions could result in damage to the
equipment
G. OPERATING LIMIT PRESSURE
CONTROL (Steam)
Set the “cut-out” (burner-off) pressure on the main scale
using the large adjusting screw. Set the differential on the
short scale by turning the small adjusting screw until the
indicator points to the desired difference between cut-out and
cut-in pressures. The “cut-in” (burner-on) pressure is the cut-
out pressure MINUS the differential. The cut-out pressure
should not exceed 90% of the safety valve setting.
H. HIGH LIMIT PRESSURE
CONTROL (Steam)
Set “cut-out” (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
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.
I. MODULATING TEMPERATURE
CONTROL (Hot Water)
Turn the knob on the front of the case until the pointer
indicates the desired setpoint temperature. The desired set
point is the center point of a proportional range. The control
has a 3 to 30° differential and may be adjusted to vary the
temperature range within which modulating action is desired.
With the cover off, turn the adjustment wheel until pointer
indicates desired range.
!
DANGER
CAUTION
To prevent burner shutdown at other than
low-fire setting adjust modulating tempera-
ture control to modulate low fire BEFORE
operating limit temperature control shuts
off burner. Failure to follow these instruc-
tions could result in damage to the equip-
ment.
J. OPERATING LIMIT
TEMPE RAT URE CONTROL
(Hot Water)
Set “cut-out” (burner off) temperature on the scale by
inserting a screwdriver through the cover opening to engage
the slotted head adjusting screw. The “cut-in” (burner on)
temperature is the cut-out temperature MINUS the
differential. The differential is adjusted from 5 to 30° F.
K. HIGH LIMIT TEMPERATURE
CONTROL (Hot Water)
Set the “cut-out” (burner off) temperature on scale using the
adjusting screw. The control will break the circuit and lock
out on a rise in water temperature above the setting. The
setting should be sufficiently above the operating limit
temperature to avoid unnecessary shutdowns. The control
requires manual resetting after tripping on a temperature
increase. To reset, allow the water temperature to drop below
the cut-out setting less differential, and then press the manual
reset button.
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