Eclipse Combustion Engineering Guide - Burnerparts

Disadvantages (continued)
And Chamber Pressure
If Air Pressure Is
Goes More
Positive (+), Then:
Stays The
Same (o), Then:
Goes More
Negative (-), Then:
Higher than gas pressure Burner goes leaner No change Burner goes richer
Same as gas pressure No change No change No change
Lower than gas pressure Burner goes richer No change Burner goes leaner
If air pressure at the burner is higher than the gas pressure (this is usually
the case), they can be made equal by installing a limiting orifice valve
between the gas control valve and burner and adjusting it until pressure
(2) equals pressure (1). However, this negates one of the advantages of
linked valve systems—the low gas pressure requirement.
• If the air supply becomes starved due to a dirty blower wheel or a plugged
filter, the system will go rich. The gas valve responds only to the mechanical
linkage, not to air flow changes.
• If multiple burners are controlled by a single set of linked valves, and the
fuel flow to one burner is throttled back manually or shut off entirely,
that fuel will go to the other burners, forcing them to run rich. In addition
to the safety hazard this presents, it makes multiple burners tedious to
set up. Any gas adjustment made to one burner upsets the settings of the
other burners in the zone.
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