Johnson Controls UL Listed GS-20 Series Manual page 13

Gas/Air Ratio (R)
Adjustment
G—UL Listed GS-20/25 and GS-40/45 Series Single-block Multi-function Gas Control Valves Technical Bulletin 13
The valve not only allows a gas/air ratio adjustment, but also an offset
adjustment (zero set), which allows for fine adjustment at lower ratios.
With these adjustments, the outlet valve pressure (P
P = R • P + Z
G A
P - P = R • (P - P
G F A
To adjust the valve, first check the factory settings. The adjustments for
the gas/air ratio (R scale) and zero set (Z scale) are located on both sides of
the gas/air ratio control module (see Figure 12). The factory settings are:
x
Gas/air ratio (R): 1:2
x
Zero set (Z):
Figure 12: Zero Set and Gas/Air Ratio Adjustments
Before starting the burner, make sure that the gas/air ratio and zero set
settings are correct for the specific appliance. If necessary, use the
hexagonal tool provided (or an acceptable Allen wrench) to adjust these
settings to the appliance manufacturer's recommendations. If the specific
ratio settings are not available, ensure that the appliance is safe to operate
at the factory settings.
Start the burner and gradually increase the output of the valve. If the
burner does not light, check for a flame during the ignition phase. If the
flame extinguishes immediately, the system may have excess air. Check
again and adjust the gas/air ratio (R) setting if necessary.
With the burner in the maximum output position, adjust the gas/air ratio
(R scale) to meet the desired flue gas analysis readings. The ratio (R) of
gas outlet pressure (P
a range of 0.6:1 to 6:1 (see Figure 13).
Check the flue gas analyses on low and high output settings without
manipulating the adjustments. Once the readings have been checked, fine
tune (by adjusting the zero set) the settings if necessary. In cases where
combustion chamber pressure (P
ratio (R) adjustment.
without combustion chamber pressure P
) + Z with combustion chamber pressure P
F
0
0
2
-
+
3
1
4
Z
5
0,6
6
) to combustion air pressure (P
G
) is used, connect it and repeat the gas/air
F
) calculates to:
G
R
) is adjustable within
A
F
F