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ThermJet, V2, Technical Information, Edition 2.14
Modulating Gas & Air
On-ratio Control or Excess Air @ Low Fire (Figure 3.1)
A burner system with modulating control gives an input
that is in proportion with the demands of the process. ANY
input between high and low fire is possible.
1. Air:
The control valve
is in the air line. It can modulate
air flow to any position between low and high fire air.
2. Gas:
The ratio regulator
allows the on-ratio amount of
gas to go to the burner. Low fire gas is limited by the
ratio regulator
. High fire gas is limited by the
manual butterfly valve
.
NOTE:
The ratio regulator can be biased to give excess
air at low fire.
NOTE:
Do not use an adjustable limiting orifice (ALO) as
the high fire gas limiting valve
. ALO’s require too much
pressure drop for use in a proportional system.
Figure 3.1 Modulating Gas & Air (On-Ratio Control or Excess Air @ Low Fire)
Multiple Burners
Automatic Shut-Off at the Burner
Multiple Burners
Automatic Shut-Off by Zone
Single Burner
NC
NC
NC
P
to other Zones
to other Burners
Main gas
shut-off
valve train
to other Burners
Automatic
shut-off at
the burner
Main gas
shut-off
valve train
P
to other Zones
to other Burners
Automatic
shut-off by
zone
to other Burners
to other Zones
Main gas
shut-off
valve train
P
Optional IF flame monitoring system controls the main gas shut-off
valve train AND ignition above 40% of maximum is NOT required.
