A.O. Smith 3400 - Manual (Page 13)

13
FIGURE 7. LOW/HIGH GAS PRESSURE SWITCH
GAS CONTROL VALVE
The gas control valve is a normally closed servo regulated gas
control valve. The valve opens only when energized by the
burner control and closes when the power is removed. The
burner control supplies 24 volts to the gas control valve during
operation.
FIGURE 8. GAS CONTROL VALVE
WATER FLOW SWITCH
The water flow switch activates when sufficient water flow has
been established. Switch will not close when water flow is not
present.
FIGURE 9. WATER FLOW SWITCH
THE CONTROL SYSTEM
The R7910A1138 is a burner control system that provides heat
control, flame supervision, circulation pump control, fan control,
boiler control sequencing, and electric ignition function. It will
also provide status and error reporting.
FIGURE 5. BURNER CONTROL SYSTEM
SPARK IGNITER
The spark igniter is a device that ignites the main burner. When
power is supplied to the igniter electrode, an electric arc is
created between the electrode and the ground terminal which
ignites the main burner.
FIGURE 6. SPARK IGNITER
LOW/HIGH GAS PRESSURE SWITCH
This XB boiler is equipped with a low gas pressure switch which
meets the CSD-1 code requirements.
The Low Gas Pressure Switch is normally open and remains
open if the pressure is below the preset pressure. It closes as
soon as the gas supply pressure is above the minimum supply
pressure.
The High Gas Pressure Switch is normally closed and is used to
detect excessive gas pressure.
CONTROL COMPONENTS
H I G H F I R I N G
RATE SETTING
L O W F I R I N G
RATE SETTING