Blue Seal Evolution Series Service Manual Download Page 14

Page: 14 / 94

Operation

Blue Seal Evolution Series Gas Convection Ranges

Amendment 13

3.2 Explanation of Control System

Safety System

The purpose of the safety system is to shut off the flow of gas if
the pilot flame goes out. It is comprised of the flame itself, the
thermocouple, and the flame failure gas valve.
The pilot flame is lit by holding in the gas control knob, which in
turn temporarily pushes the plunger inside the safety valve
open and allows gas to flow through. Once the burner is lit, the
thermocouple will begin to generate millivolts (after about 10 to
30 seconds of being heated) and will energize the
electromagnet inside the gas valve. Once energized the
electromagnet holds the plunger inside the gas valve in the
open position. The plunger has to be pushed all the way in for
the electromagnet to be able to hold it in place.
If the burner flame goes out for some reason, the thermocouple

will cool after about 10 to 30 seconds and stop generating
millivolts. The electromagnet will then de-energize, and the
plunger will snap shut, cutting off gas flow.
Detail of each component in the safety system is explained
below.

Millivolts are provided to the electromagnet by the
thermocouple (not shown) which generates millivolts when
heated. The thermocouple screws into a fitting at the back of

the gas valve to make an electric connection. By pressing in the
gas control knob, the plunger can be temporarily held open
while lighting.
There's two reasons for this; gas has to flow through the safety
valve to make it possible to light the pilot burner, and secondly
the plunger has to be pushed all the way in for the
electromagnet to hold it in. i.e. the electromagnet is strong
enough to hold the plunger in once there, but is not strong
enough to pull it in by itself. Sometimes a problem with the
flame not staying lit after releasing the button can be attributed
to not pushing the plunger all the way in.
The Fault Finding Charts at Section 5 should be used to identify
any incorrect operation. On correct identification of the
operating fault the Fault Finding charts will make reference to
the corrective action required, or refer to the Fault Diagnosis
section and / or Service section to assist in correction of the
fault.

The tip of the thermocouple is located in the pilot burner flame
and the nut at the other end of the thermocouple screws into
the back of the gas valve. Inside the copper tubing is a wire

which is joined at the tip but insulated from the rest of the
tubing. These two parts (the copper tubing and wire) make up
the "wiring" for an electrical circuit. When these two dissimilar
metals, wire and tip, are heated an electrical voltage is
produced.
This type of thermocouple generates between 7 and 30
millivolts when heated in the pilot flame.

Electromagnetic Flame Failure Gas Valve

The purpose of the safety valve is to shut off the flow of gas if
the pilot flame goes out.
Inside the body of the gas valve is an electromagnet connected
to a spring loaded plunger. When the electromagnet is
energized, it holds the plunger in, allowing gas to flow through
the valve. When the electromagnet is de-energized, the
plunger snaps to the closed position, stopping the flow of gas.

Figure 3.2a

Insulator

Nut

Conductor

Tip

Internal
Wire

Thermocouple

The thermocouple is a device that generates electricity when
heat is applied to the tip.

Figure 3.2b

Thermocouple

Gas flow

Electromagnet