Siemens LMV5 Series Technical Instructions page 202
Linkageless burner management system
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Technical Instructions
Document No. LV5‐1000
3. If the fixed air inlet damper and / or the fixed stack damper are adjusted to provide adequate
differential pressure across the FGR valve at low fire, pressure drops across these fixed dampers at
high fire will be high, requiring a larger blower.
Small pressure changes (pressure inside a boiler room vs the pressure in the stack) are common. These
are typically due to doors being opened and closed in the boiler room and convective effects in the
stack. Depending on the installation, these changes might be non‐existent or they might be as large as
2" WC. With the arrangement shown in Figure 6‐12, even small pressure changes can cause the FGR
flow to be non‐repeatable. A few examples are given below:
Example: At low fire, the differential pressure across the FGR control valve is 0.2" WC. Some external
change increases P1 by 0.2" WC. This represents a very small absolute change in pressure, but a 100%
change in the differential pressure across the FGR control valve which will lead to a large percentage
change in FGR flow.
Example: At high fire, the differential pressure across the FGR control valve is 6.0" WC. Some external
influence increases P1 by 0.2" WC. This represents a very small absolute change in pressure and a 3.3%
change in differential pressure across the FGR control valve. This will lead to a negligible percentage
change in FGR flow.
Figure 6‐12: FGR Burner with no VFD and an Air Damper on the Blower Outlet
Section 6
Page 30 SCC Inc.
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