13
ThermJet, V2, Technical Information, Edition 2.14
Bypass Start Gas (Optional) (Figure 3.5)
A bypass start gas circuit provides gas flow around zone
gas control valves during the trial for ignition period. This
should only be used if excess air (proportional or fixed air
control) is being used on low fire; it should NOT be used
with on-ratio low fire systems.
During the trial for ignition period, the solenoid valve in the
bypass line plus the automatic gas shut-off valve (either at
each burner or each zone) are opened. If a flame is
established, the bypass solenoid valve closes at the end
of the trial for ignition period. If a flame is not established,
then the bypass solenoid valve and the automatic gas
shut-off valve close.
Figure 3.5 Bypass Start Gas Circuit Schematics
Main gas
shut-off
valve train
NC
Bypass option
Main gas
shut-off
valve train
Bypass option
NC
NC
Bypass option
Main gas
shut-off
valve train
High/Low Air and
Gas Control
Modulating Gas with
Fixed Air Control
High/Low Gas with
Fixed Air Control
