Adjustment Procedures
6-6
750-211 (revised 2009)
Promethean Boilers, Model 4WI Manual
Separate and independent controls affect modulated firing and burner on-off cycling. The Firing Graph depicts a
typical setting relationship of the operating limit control, modulating control, and the high limit control.
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.
FIGURE 6-6.
Firing Graph
In normal operation, the burner will shut down whenever the pressure or temperature rises above setting
A
. At that
point the switch in the operating limit control will open. As the pressure or temperature drops back to
B
, the oper-
ating limit control closes and the burner will restart. The modulating control will signal the modulating motor to be
in a low-fire position. If the load demands exceed the low-fire input potential, the modulating control will increase
the firing rate proportionately as pressure or temperature falls toward point
D
. The modulating motor will stop at
any intermediate point between
C
and
D
whenever the fuel input balances the load requirement.
As the load requirement changes, the firing rate will change accordingly. This it is referred to as modulated firing.
Point
D
represents the maximum firing rate of the burner, or high-fire. In the event pressure or temperature drops
while the burner is firing at high-fire, it indicates that the load exceeds the capacity of the boiler.
The Firing Graph shows that point
B
and point
C
do not coincide. Extreme load conditions could require the
points be closely matched.
Summary of Contents for 4WI
Page 46: ...Burner Operation and Control 2 22 750 211 revised 2009 Promethean Boilers Model 4WI Manual...
Page 62: ...Waterside Care and Requirements 3 16 750 211 revised 2009 Promethean Boilers Model 4WI Manual...
Page 70: ...Sequence of Operation 4 8 750 211 revised 2009 Promethean Boilers Model 4WI Manual...
Page 114: ...Adjustment Procedures 6 28 750 211 revised 2009 Promethean Boilers Model 4WI Manual...
