5
Figure 2–Ratiomatic Operation
Main Gas
Adjusting
Valve
Pilot
Adjusting
Valve
Set-Up & Operation
Against Back Pressure
(Positive Chamber Pressure)
Set-Up & Operation
Against a Draft
(Negative Chamber Pressure)
OR
OR
Set-Up & Operation
(Neutral Chamber Pressure)
120
100
Air
Gas
80
60
40
20
0
Low Fire
% of Neutral High Fire Flow
High Fire
Excess Air
120
100
Air
Gas
80
60
40
20
0
Low Fire
% of Neutral High Fire Flow
High Fire
Excess Air
120
100
Air
Gas
80
60
40
20
0
Low Fire
% of Neutral High Fire Flow
High Fire
Excess Air
Air Valve Settings:
• Factory Set–fully open at high fire, fully closed
at low fire.
Results:
• High fire is increased.
• Low fire is increased.
• Turndown ratio is unaffected.
• To reduce high fire, use an end limit switch
to reduce motor travel.
Air Valve Settings:
• Factory Set–fully open at high fire, fully closed
at low fire.
Results:
• Normal high fire.
• Normal low fire.
• Normal turndown.
Air Valve Settings:
• Factory Set–fully open at high fire, fully closed
at low fire.
Results:
• High fire is increased.
• Low fire is normal.
• Turndown ratio is decreased.
• To limit air valve overtravel at high fire, use an
end limit switch to reduce motor travel.
1
Control Motor
Rotates air valve:
Open for more heat
Closed for less heat
3
Proportionator
Changes gas flow
in proportion to
loading line pressure;
Higher pressure = more gas
Lower pressure = less gas
12
4.0 Start-Up And Adjustment
(continued)
Step 5: Adjust Low Fire Flame
Return the control motor to the low fire position.
Check the combustion air differential pressure as discussed in Step 2.
Gas pressure drop across the burner
will be too low to read reliably, but the
flame should be clear blue as shown
on the cover of this manual, entirely
within the firing tube, and tight on the
burner head.
If necessary, adjust the ratio regulator bias
screw as shown below to obtain the proper low fire flame. If the
flame cannot be viewed, adjust the bias screw to produce the mini-
mum gas flow that will generate a steady flame detector signal of
sufficient strength.
After adjusting low fire flame, return to high fire and check gas differential pres-
sure as described in Step 4.
Step 6: Check Settings & Shut Down
Cycle the burner from high to low several times to check repeatability of settings.
To make it easier to set up and troubleshoot the burner in the future, record your
setup data below.
Do not turn the blower off until the chamber temperature is below 250
°
F (121
°
C).
This will prevent hot gases from flowing back through the burner and blower and
damaging them.
Remove Cover & Turn Screw
Clockwise for more low fire gas,
Counterclockwise for less low fire gas.
Low Fire
High Fire
Combustion Air Pressure Drop
between Tap "A" & Chamber, "w.c.
Gas Pressure Drop between
Tap "B" & Chamber, "w.c.
Gas Pressure into
Proportionator, "w.c.
Gas Pressure into
Pilot Gas Cock, "w.c.
Flame Signal
Burner Model ______________________
Low Fire
Gas Adjustment
Factory set for most applications;
can be field adjusted if necessary.
Air Valve
2
Loading Line
Transmits air pressure
changes to Ratio Regulator
