MN702GE 060320
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702GAS overview
The Model 702GAS burner is a low-high-low (step modulating) burner that
utilizes a damper motor to control air (and gas fuel rate).
See the next page for gas train component locations.
Operation
Ignition for main flame is accomplished by a proved gas pilot of approximately
70,000 Btuh. Pilot gas is introduced and ignited by a Carlin 9,000-volt elec-
tronic ignitor wired to the electrode. After the pilot flame is proven, the two
main gas safety valves open. The pilot gas valve closes after a time delay
to allow main flame to establish. Flame is monitored both for pilot flame and
main flame with a UV scanner positioned in the mounting flange. The burner
main flame begins at low fire. If additional input is required, the damper mo-
tor opens the gas butterfly valve and air damper to their high fire positions.
Gas is introduced into the burner through a manifold around the air tube. The
gas then circulates through a set of four orifice spuds into the air stream,
upstream of the retention ring. The spin of the air flow at the retention ring
thoroughly mixes the gas/air before it reaches the combustion zone.
Firing rate adjustment
•
Then gas flow is adjusted to match the air flow at low and high fire rates.
NOTE: High Fire must be set before Low Fire.
•
See the “Starting and operating” section on page 12 of this manual for
the complete description of the adjustment process. The following is a
brief summary only.
•
High-fire air is set by adjusting the combustion head position (to control
air flow through and around the retention ring).
•
Low-fire air is then adjusted by altering the position of the low fire adjust-
ing screw.
Gas pressure requirements
Standard gas train requirements for the 702GAS burner requires a minimum
w.c. inlet of 5" under flow conditions (maximum 14"). Systems with high pres-
sure (above 14" w.c.) require a line pressure regulator upstream.
1. The Carlin Model 702GAS burner