Figure 4-25.Typical Bunsen burners.
Figure 4-26.Bunsen type of burner.
pressure is above the desired pressure. When the gas
pressure to the burner is low, the pressure-regulating
spring pushes the diaphragm down, in turn, pushing
the pilot valve down. When the pilot valve opens,
supply pressure is applied to the top of the operating
piston. As the operating piston moves down, the main
valve opens, admitting supply pressure to the burner.
As burner pressure rises, the diaphragm is pushed up
against the pressure-regulating spring, closing the
pilot valve. This removes the supply pressure from the
top of the operating piston and the piston return spring
pushes the piston up, closing the main valve. The
regulator is thus closed every time the burner pressure
gets above the desired amount. Turning the adjusting
screw at the top can vary the setting of the regulator.
SOLENOID GAS VALVE.The
principles of construction and operation applied in all
solenoid gas valves are similar. However, the design of
each individual unit differs somewhat from the others.
The two most common types of solenoid gas valves are
the standard solenoid valve and the recycling solenoid
valve discussed in the following paragraphs.
The standard solenoid gas valve shown in figure
4-29 is of the electric type. It is suitable for use with
gas furnaces, steam and hot-water boilers, conversion
burners, and industrial furnaces. This valve operates
when a thermostat, limit control, or other device closes
a circuit to energize the coil. The energized coil
operates a plunger, causing the valve to open. When
there is a current failure, the valve automatically closes
because of the force of gravity on the plunger and valve
stem. The gas pressure in the line holds the valve disk
upon its seat. To open this valve during current failure,
use the manual-opening device at the bottom of the
valve. When the electric power is resumed, you should
place the manual-opening device in its former