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GM-4_6_
(Dual On/Off
with Gas/Air
Ratio Control)
G as
L ine
G—GM-20/25 and GM-40/45 Series Dual-block Multi-function Gas Control Valves Technical Bulletin 15
This valve provides mechanical modulating control of the gas outlet
pressure at a consistent ratio to the main air blower pressure. An example
of a typical installation is shown in Figure 12. The burner control responds
to a higher demand for heat by increasing the amount of air being supplied
to the burner, resulting in an increased air pressure. With the air pressure
(P
) connected to the valve, the valve seat position is controlled to achieve
A
the optimum outlet gas pressure according to the preset gas/air ratio.
The combustion chamber pressure (P
combustion quality in cases where the combustion chamber pressure is
significantly higher during operation than atmospheric pressure.
G M S erie s C om b inatio n C o n trol
O ptio na l
P re ssure
S w itch
M an ual
S h utoff
Valve
Filte r/
S trainer
A ir L ine
Figure 12: Typical Application Installation
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
F
) can be connected to improve
F
S o le noid
Valve W o rking
w ith Con tro lle r
P
P
G
S o le noid
Gas/Air
Valve
Co ntroller
M
without combustion chamber pressure P
) + Z
with combustion chamber pressure P
B o iler
P
F
A
) calculates to:
G
F
F
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