Chapter 1 — Basics of Firetube Operation
Part No. 750-184 1-9
6. Auxiliary Low-Water Cutoff (Optional): Breaks the circuit to stop
burner operation if the water level in the boiler drops below the
master low-water cutoff point.
7. Safety Valve(s): Relieves the boiler of pressure higher than the
design pressure or a lower pressure, if designated. Relief valves
and their discharge piping are to be installed to conform to ASME
Code requirements.
F. IFGR COMPONENTS (CB-LE)
1. Flue Gas Transfer Port, IFGR Damper, and Flange Collar (Figure
1-6). The flue gas transfer port is a tube that allows the flue
gases to travel from the exit of the fourth-pass tubes to the
entrance of the combustion air fan. The IFGR damper controls
the volume of flue gas induced into the combustion air stream.
The damper is located in the flue gas transfer port and is
positioned by the control linkage.
2. IFGR Damper Linkage (Figure 1-7). The IFGR damper is
positioned by the control linkage. The linkage could consist of a
single arm, or it could consist of several arms driven from the
jackshaft to provide modulating control (see Figure 1-16).
3. Over-Travel Mechanism. The over-travel mechanism has two
functions. It allows the linkage to pass through the front door,
and it allows jackshaft rotation to exceed (over travel) IFGR
linkage movement. A set of springs allows the linkage to stay in
a fixed position while the jackshaft rotates.
4. Fuel Change-Over Linkage. When a boiler is equipped to fire
either gas or oil (dual-fuel boilers), and the required NOx levels
are below 60 ppm on natural gas, a dual-linkage arrangement is
used to provide the different recirculation rates required for each
fuel. Two jackshaft drive arms are provided, one for oil and one
for gas. The linkage is manually connected to the appropriate
arm, based on the fuel being used. On dual-fuel boilers with two
jackshaft drive arms, as defined above, a proximity switch is
used to prove that the correct linkage connection is made. (Refer
to the wiring diagram provided with the boiler.)
5. Fan/Motor Cassette. The fan and motor assemblies are designed
as a cassette so that they can be removed from the front of the
boiler, without opening the front door. The front door davit arm
can be used to remove the assembly.
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