Low Gas Switch; Low Gas Pressure Switch; Gas Valve; Flow Switch - A.O. Smith VB/VW 1500, 2000 Instruction Manual

LOW GAS SWITCH

This VF boiler is available with a low gas pressure switch which
meets the CSD-1 code requirements, see Figure 5.
The Low Gas Pressure Switch (LGPS) is normally closed and remains
closed unless the pressure falls below the preset pressure.

LOW GAS PRESSURE SWITCH.

GAS VALVE

The Gas valve is a normally closed servo regulated gas valve. The
valve opens only when energized by the MCB control board and
closes when the power is removed. The MCB supplies 120 volts to
the gas valve during operation.
FIGURE 5.

FLOW SWITCH

The flow switch pictured in figure 6 activates when sufficient flow
has been established. Switch will not close when flow is restricted
or is not present
FIGURE 6. WATER FLOW SWITCH.

FLAME SENSOR

Each Boiler is equipped with two flame senors coupled together to
detect the presence of the burner flames at high and low fire conditions.
These flame rods work together as one to sense the flame. If no
flame is sensed, the gas valve will close automatically. On standard
models if no flame is sensed on three ignition trials, the boiler will
lock out. In the event of a lockout, depress the SELECT button on
the display board to restart the boiler.
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