Page 33
Section D - Fuel and Electrical Systems
JBE(X) Manual
manufacturer. In all cases, these controls must be
integrated together.
7. Operating and Modulating Control
Burner operation, for on-off cycling and modulation are
controlled by the boiler steam pressure or hot water
temperature variation from set point. Parallel positioning
systems generally use sensors to measure temperature
or pressure and are programmed in a unique method, not
covered in this manual. Refer to the control manual, pro-
vided with the burner, for complete details on setting
the controls.
The standard equipment will include a high limit control, an
operating control and a modulating control (not normally
supplied with the burner). All of these controls are piped
to the steam or hot water piping connected to the vessel.
These three controls must be adjusted to function together
or the burner will operate inefficiently and provide poor
system response. If excessive on-off cycling occurs, the
components will wear out prematurely. Figure D-8 shows
the relationship between the temperature or pressure and
burner firing rates.
The high limit control senses the hot water temperature
(vessel outlet) or steam pressure. It is used as a safety
limit to turn the burner off if the operating control fails. If this
limit is tripped, the burner will remain off and will have to be
manually reset. The high limit control should be set
sufficiently above the operating control (pressure or
temperature) to avoid nuisance shutdowns. The high limit
control cannot be set above the temperature rating of the
vessel or connected piping. This point is indicated on the
far right of Figure D-6 and represents the highest
temperature or pressure available.
The Operating Control senses the temperature or
pressure and automatically turns the burner on to initiate
the startup sequence when the temperature or pressure
drops below the “Burner On” point (“B” on Figure D-8)
and initiates the shut down sequence when the load is
satisfied and the temperature or pressure rises above
the “Burner Off” point (“A” on Figure D-6).
The modulating control senses the temperature or
pressure and signals the modulating motor to set the
fuel and air input rates at a level consistent with the
indicated temperature or pressure. An increasing load
will cause the temperature or pressure to drop and
the modulating motor will sense this lower level and
increase the fuel and air input accordingly, starting
modulation from low fire at point “C” and arriving at
high fire at point “D” (Figure D-6). This control must be
set to allow normal shutdown at low fire.
As Figure D-6 shows, there should be clear separation
between each of the control points for the system to
work properly. If the controls are positioned too close
to each other, or even overlapping, the burner will have
excessive ON-OFF cycling that reduces efficiency,
increases wear and can cause premature failure of the
components. Standard burner motors in the JBE(X)
size range should not cycle on and off any more than 2
to 4 times per hour.
8. Flame Safeguards
Several different FSG (Flame Safeguards) are offered
for the JBE(X). They all perform the common function
of controlling the process of pre-purge, pilot trial for
ignition, main trial for ignition and flame safety as well
as monitoring limit switches and sensors. The ac-
tual details of operation can vary. The manual for the
specific FSG is included with the burner and should be
studied prior to installation, startup or operation.
The operating sequence, especially the sequence of
when the limit switches are checked, will be an
important tool in troubleshooting the burner.
0 %
100 %
Burner Off
Minimum
Input
(Low Fire)
(High Fire)
Firing Rate Increasing
Modulating Firing
Range
D
Modulation Control
(Modulated Burner Input in Response
to Temperature or Pressure Change)
C
B
A
Operating Control
Cycle Burner On and Off at these
Temperatures or Pressures
High Limit Control
Safety Shutdown
Turn Burner Off at
this Temperature or
Pressure
“ON - OFF”
Differential
Falling Temp.
or Pressure
Rising Temp.
or Pressure
(Burner OFF)
(Burner OFF)
(Burner ON)
Boiler Water Temperature or Steam Pressure Increasing
Figure D-6
Operating and Modulating Control
