17
Midco International Inc.
8471 95
WARNING: Explosion hazard. Do not use any electronic device if it gets wet.
It can malfunction and cause serious injury or death. Replace any device that
has been wet.
DANGER: Do not tamper with the unit or controls. If trouble occurs contact the
installing contractor, service agency, or fuel supplier. See front cover.
DANGER: Be sure that the main and pilot manual Shut-O
ff
Valves are closed and
the burner power supply is turned o
ff
before removing any parts for service.
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The air-fuel modulation is achieved through the relationship of the supplied air pressure and the
output gas pressure. The motor used in this burner is variable speed. By using this air pressure
relation in the blower, output gas pressure can be varied relative to the air pressure through a ratio
regulator.
Refer to Figure 9- (see page 29) which shows air pressure pickup at the blower outlet. The air
sensing tube is connected to the ratio regulator. When the blower is modulating to a certain speed,
the pressure in the housing causes the ratio regulator to open. It is a linear relationship between
the air pressure and the gas pressure. The temperature control or operating control sends a heat
input signal (2-10 VDC) to the blower; as a result, the blower pressure causes the gas to modulate
through the ratio regulator.
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Part 2 - Service - SCEBM-2 Module
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X Modulation
Methodology
Part 2 Service - SCEBM-2 Module