750-204
Profire D/LND
8-5
8.4 — FGR Control Valve
8.4 — FGR Control Valve
The FGR control valve is mounted to an FGR
damper on the burner. A burner mounted
modutrol motor with linkage connections coordi-
nates the air, fuel, and NOx control devices to
provide proper fuel/air/NOx ratios through the fir-
ing range. The modutrol motor must be able to
complete its full travel range. Restrictions will
damage the motor and/or the linkage. Linkage
consists of adjustable levers, rods and ball joints
that transmit motion from the modutrol motor to
the FGR control valve. Lever and rod adjustments
should be made with the motor in the low fire
position. The angles of the driven levers on the
modutrol motor jackshaft can be adjusted to vary
the rate of change. The closer the rod is to the
lever hub, the less distance the rod and control
valve blade will travel.
FIGURE 8-3. FGR Control Valve and Air/FGR Damper
8.5 — Air/FGR Damper Assembly
The air/FGR damper regulates the volume of combustion air. Position of the rotary damper blade is controlled by
a modutrol motor.
The damper blade in the low fire position is normally approximately 1” open at low fire. The air/FGR damper and
FGR control valve blades open as the modutrol motor drives toward the high fire position where the flue gas is
pulled into the regulated combustion air flow above the damper blade as controlled by the FGR control valve.
Combustion air mixed with flue gas is passed on through the blast tube to the combustion zone.
Before starting the boiler, make sure the control valve is closed. The boiler must never be operated if the control valve
is open. This will result in hot combustion gases flowing backwards in the system. This will damage the system and
can cause bodily harm.
!
Warning
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