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.
Pressure Switch Connection
See Figure 4 for typical connection of a circulating fan limit switch.
Limit Controls & Saftey Equipment
Limit controls and safety equipment should comply with current NFPA Stan-
dards* 86 and 86C, and all applicable local codes and/or standards.
*Available from:
National Fire Protection Association
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
Gas Inlet
Manifold
Check Valve Opens When
Gas Inlet Pressure Is at Low Fire
Process Air
WARNING!
Do Not Install Any Valves Here!
See Section 2.0
Tee
P
Lo
Hi
Circulating Air
Pressure Switch
Tube Points
Upstream
Tube Points
Downstream
Profile Plate
5
Figure 5–Profile Plates & Duct Design
where
A
G
= Area in of the gap between the profile plate
and the burner.
Flow
T
= Total air flow around and through the
burner.
Flow
R
= Air flow required per unit of open area to
produce the specified pressure drop.
A
NF
= Burner net free area, from page 2
L
F
= Burner length.
A
G
=
– (A
NF
x L
F
)
Flow
R
Flow
T
Example
–Size a profile plate for a seven foot long burner
to fire at 800,000 Btu/hr. Air flow around and through
the burner will be 60,000 scfm.
Flow
T
= 60,000 scfm
Flow
R
= 21.5 scfm per sq. in. (from page 2)
A
NF
= 10 sq. in. per ft. (from page 2)
L
F
= 7 ft.
To calculate the open area between the burner perime-
ter and the edge of the profile plate opening, solve the
following equation:
A
G
=
– (10 x 7) = 2720 sq. in.
60,000
21.5
The profile opening must provide uniform air flow down
the length of the burner.
If the exact air flow is in doubt, provide adjustable profile
plates so that final settings can be made in the field.
Profile plates should be positioned flush with the firing end
of the burner. If necessary the plates can be located up
to l/2" back from the firing end, but
under no circum-
stances
should they be in front of the burner.
Center the burner in the duct.
Allow a minimum of 46" (1168 mm) from burner to near-
est point of possible flame impingement at an input of
800,000 Btu/hr/ft (770 kW/m).
Profile Plate Design & Mounting Guidelines
Profile
Plate
Burner
As
Required,
Top & Bottom
6" Min.
Top &
Bottom
Duct
Width
Duct
Height
3" Min.
4" Max.
Both Ends
6" Min.
Both
Ends
Duct Lengths
Minimum Distance Before
Possible Flame Impingement = 46"
AH-O
Burner
Minimum Distance Before Transition
Rectangular Ducts: One Height or Width, Whichever is Greater
Round Ducts: One Diameter
7.5°
Maximum
Air Flow
