27
Main Burner Adjustment
1. Once the pilot has been properly established, the manifold gas pressure or temperature rise should be
adjusted to nameplate or design specifications. The gas pressure regulator is adjusted at the factory
for average gas conditions. It is important that the gas supplied to the burner is in accordance with the
input rating on the rating plate.
See “Gas Pressure” on page 10.
2. Create a high fire call for heat. This should be done with the blower on and all gas controls on. High fire
can be achieved by removing the wire at terminal #4 (remove wires #2 and #4 for Maxitrol 44 systems)
from the Maxitrol 14 amplifier.
3. The manifold pressure should be checked at the pressure gauge downstream of the modulating valve.
indicates the proper manifold pressure for the desired amount of BTUs per foot of burner.
For natural gas systems, the high fire manifold pressure should not exceed
5 inches wc
. For propane
gas, the high fire manifold pressure should not exceed
2.5 inches wc
.
Another method of checking
high fire is to measure the temperature rise of the unit. The temperature rise should be set to design
specifications and typically is minimum 70°F.
4. Every unit has a specific design manifold gas pressure based on CFM and temperature rise. Refer to
the unit’s nameplate for the design manifold gas pressure.
5. Remove the cap from the combination gas valve for regulator adjustment.
6. Use the regulator pressure adjusting screw to adjust the high fire manifold pressure to design
temperature rise (
5 inches wc
maximum for natural gas and
2.5 inches wc
maximum for propane
gas). High fire should be set to generate the design temperature rise. If the high fire screw is at the end
of its adjustment and more pressure is needed, then adjust the main building gas pressure regulator
spring (located external to the unit) to achieve the proper manifold pressure. Turning the regulator
screw clockwise will increase pressure and counter-clockwise will decrease pressure.
7. Reconnect the wire on the Maxitrol 14 amplifier at terminal #4 (wires #2 and #4 for Maxitrol 44).
8. The low fire manifold pressure must now be set. Low fire can be achieved by removing the wire at
terminal #5 from the Maxitrol 14 amplifier (remove #8 for Maxitrol 44).
9. Locate the bypass screw (under the cap of the valve - location #1), refer to
.
10. Adjust the low fire manifold pressure until there is a very thin flame along the entire length of the
burner. No dark spots should be seen in the burner. The burner may be observed through the view-
port located on the external wall of the heater. Replace the cap to the valve. Make sure all wiring and
gas components are connected and operational.
11. A final gas leak check shall be performed to verify the gas-tightness of the heater’s components and
piping under normal operating conditions. This can be done by measuring the gas pressure at the
1/4” gas plug just downstream of the modulating valve.
Figure 15 - High Fire/Low Fire Bypass Screw Setting
Firing Mode
Low Fire = 0-5V DC
Modulation = 5-15V DC
High Fire = 15-24V DC
Modulating Valve
Adjustment Screw Location
Содержание D76
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