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Zero Set (Z)
Adjustment
14 G—UL Listed GS-20/25 and GS-40/45 Series Single-block Multi-function Gas Control Valves Technical Bulletin
P
- P
(in. W.C.)
G
F
P
(in. W.C.)
G
With the correct gas/air ratio (R) set, there may be some minor deviations
(caused by friction, etc.) at very low pressures. To allow for fine
adjustment of the valve, the zero set can be changed. The zero set adds a
constant offset to the flue gas analyses, affecting the low output figures
more significantly than the high output figures.
Zero set (Z) can be accomplished by a parallel shift of the characteristic
curve from -2 to +2 mbar (-0.8 to +0.8 in. W.C.) (see Figure 13).
Set the burner to the low fire position, perform a flue gas analysis, and
vary the outlet pressure by adjusting the Z scale until the desired flue gas
analysis readings are obtained.
If adjusting the zero set (Z) results in an unacceptable high output figure,
repeat the adjustments starting with the gas/air ratio (R) adjustment
procedure.
5:1
3:1
6:1
20
2:1
16
12
8
4
0
8
0
4
P
(in. W.C.)
A
P
- P
(in. W.C.)
A
F
Figure 13: Analyses Chart
1:1
0.7:1
Z
0.6:1
16
20
12
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