4
2.0 Control System Requirements
Turndown Method
Input is normally controlled by a motorized butterfly valve in the gas line to the burner.
Regulator Loading Lines
Connect the top diaphragm chambers of the main gas and pilot gas regulators to the
duct approximately 10" downstream of the burner. This will allow the regulators to
maintain a constant supply pressure to the burner regardless of varying pressures in
the duct.
Piloting
Pilot gas flow is adjusted as shown in Figure 6.
Ignition
Ignition voltage should be 6000 VAC.
Check Valve
See Figure 3. At high fire, the gas pressure at the burner inlet is higher than the air
pressure, and the check valve is closed. At low fire, gas pressure falls below the air
pressure, and the check valve opens, permitting a small amount of air to mix with the
gas. This premix at low fire stabilizes the flame and helps distribute the flame evenly
down the length of the burner.
Air Damper
Install an air damper at the combustion air blower inlet, or between the blower and the
burner to allow adjustment of combustion air flow.
Pressure Switch Connection
See Figure 4 for typical connection of combustion air and circulating fan limit switches.
Limit Controls & Safety Equipment
Limit controls and safety equipment should comply with current NFPA Standards* 86
and 86C, and all applicable local codes and/or standards.
*Available from:
National Fire ProtectionAssociation
American National Standard Institute
Batterymarch Park
1430 Broadway
Quincy, MA 02269
New York, New York 10018
Warning
Do not install any valve or controlling device in the gas line between the burner
and the check valve tee, Figure 3. Because this section of the gas line carries a
partial pemix at low fire, it is possible under unusual conditions for the flame to
travel back through the pipe to the tee. Devices installed in this section may be
damaged and may melt, releasing gas to the atmosphere and causing fires or
explosions.
Figure 3–Check Valve Operation
Figure 4–Pressure Switch Location
P
Hi
Lo
Blower
Pressure Switch
P
Lo
Hi
Circulating Air
Pressure Switch
Tube Points
Upstream
Tube Points
Downstream
Tube at
Blower Inlet
Burner Air Tap
See Figure 7
Gas Inlet
Manifold
Check Valve Opens When
Gas Inlet Pressure Is at Low Fire
Combustion Air
WARNING!
Do Not Install Any Valves Here!
See Section 2.0
Tee
5
Figure 5–Mounting & Duct Lengths
• Provide at least 3" (76 mm) clearance between burner
and top, bottom and sides of the duct.
• Profile plates are not required for good burner opera-
tion, but uniform velocity must be maintained for full
length of burner. If velocity is not uniform, use profile
plates to correct it.
• Center the burner in the duct.
• Allow a minimum of 46" (1168 mm) from burner to
nearest point of possible flame impingement at an
input of 1,000,000 Btu/hr. (962 kW/m).
• Support the blower and motor independently of the
burner.
Maximum
Downstream
Temp.
1500°F
(815°C)
Min./Max. Velocity:
500 to 6000 fpm
2.54 to 30.48 m/s
1000 to 4000 fpm
5.08 to 20.32 m/s
Optimum Velocity
:
NOTE:
The blower and the adjoining duct (shown in the darker
shaded areas) are not part of the burner assembly; they
must be purchased and installed separately.
Maximum
Upstream
Temp.
750°F
(400°C)
Duct Lengths
3.0 Duct Design and Burner Mounting
Duct Design
See Figure 5 for typical mounting arrangements and duct designs.
Support
The mounting brackets supplied with the burner are capable of supporting the weight
of the burner. Support the blower and air manifold independently of the burner.
Air Manifold
The air manifold must be large enough to supply the required combustion air flow with
minimum pressure drop. Do not use more than one 90
°
bend between the blower and
the burner air inlet.
Valve Train Support
Support valve trains independently of the burner.
Gas Piping
Use flexible nipples to allow for thermal expansion of the burner.
Check Valve Piping
Gas flow through the check valve must be horizontal. See Figure 3.
Gas Piping Standards
Gas piping must comply with American National Standard entitled "National Fuel Gas
Code"* (NFPA No. 54 or ANSI Z223.1), or must be acceptable to the authority having
jurisdiction.
Wiring Standards
Electrical wiring must comply with the National Electric Code*, (NFPA Std. 70 or ANSI-
CI 1981), or must be acceptable to the authority having jurisdiction.
*Available from:
National Fire Protection Association
American National Standard Institute
Batterymarch Park
1430 Broadway
Quincy, MA 02269
New York, New York 10018
Minimum Distance Before
Possible Flame Impingement = 46"
RAH
Burner
Minimum Distance Before Transition
Rectangular Ducts: One Height or Width, Whichever is Greater
Round Ducts: One Diameter
7.5°
Maximum
Air Flow
