Chapter 5 Adjustment Procedures
5-4 750-177
If points B and C overlap when restart occurs, the burner would drive to a higher firing position immediately
after the main flame was proven.
Note: It is not recommended that the boiler controls be set so as to overlap the modulating control
range and operating control range.
High Limit
Control Safety
Shutdown
“ON - OFF”
Differential
Modulated
Firing Range
Firing Rate
100
0%
Minimum Input
(Low Fire)
Burner Off
Increasi
Falling Temp. or
Pressure
Rising Temp.
or Pressure
Increasi
Increasing
(Burner ON)
(Burner OFF)
(Burner OFF)
Boiler Temp.or Press
Operating Limit
Control Response
Modulation Control
Response
D
C
B
A
Figure 5-1: Firing Graph
When firing a cold boiler, it is recommended that the burner be kept at low fire, under manual flame control,
until normal operating pressure or temperature is reached. If the burner is not under manual control on a cold
start, it will immediately move toward high fire as soon as the program control releases the circuit that holds
the burner in low fire. The modulating control will be calling for high fire and the burner will move to that position
as rapidly as the damper motor can complete its travel.
Note: Rapid heat input can subject the pressure vessel metal and refractory to undesirable conditions.
Do not operate the boiler in excess of 90% of the safety valve relief setting. The closer the operating pressure is
to the safety valve relief pressure, the greater the possibility of valve leakage. Continued leakage, however slight,
will cause erosion and necessitate early safety valve replacement. The control settings on a hot water boiler must
be within the temperature limits of the boiler.
Ideally, the boiler operating controls should be set under
actual load conditions. Especially under new
construction conditions, the boiler is initially started and set to operate under less than full load requirements.
As soon as possible thereafter, the controls should be reset to provide maximum utilization of the modulating
firing system. To accomplish maximum utilization, and assuming that air/fuel combustion ratios have been set,
make the required adjustments to the controls to bring the boiler pressure or temperature up to meet the load
requirements.
To Next Page
Loading...
Need help?
General
