750-204
Profire D/LND
8-7
8.6 — Blast Tube Temperature Interlock (optional)
8.6 — Blast Tube Temperature Interlock (optional)
A blast tube temperature interlock device monitors air temperature in the blast tube area of the burner. If the
blast tube temperature rises above 200º F maximum. An external scanner is used on the low emission burners.
8.7 — Stack Temperature Interlock (optional)
A stack temperature interlock device monitors flue gas temperature in the stack. The stack temperature interlock
is used as a low fire hold device. The stack temperature interlock is set at 25º F below the minimum stack tem-
perature at low fire (nominal 200º F). After the stack temperature rises above the set point, the interlock stack
temperature rises above the set point, the interlock closes and allows the burner to modulate.
8.8 — 20 PPM Design
The 20 ppm design features a dual gas manifold. Each zone is controlled by a butterfly valve linked to a 14 point
adjustment cam. The primary large butterfly valve controls the main gas orifices and the secondary small butter-
fly valve controls the pre-mix gas spuds. See Figures 8-5 and 8-6.
FIGURE 8-5. Secondary Gas Valve
Refer to the adjustment section to setup the burner. In the low fire position, the secondary valve controlling the
pre-mix spuds is almost closed. After all adjustments are made throughout the modulating range, go back and
relight the burner. Upon startup, check that the fire is not burning behind the diffuser. If this happens, close the
secondary valve until this situation is corrected. Repeat several times.
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