3
Operation
10
©
Moffat Ltd, January 2007
Revision 1/
Blue Seal Evolution Series Gas Salamander
3.4
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
have been 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 the flow of gas.
Detail of each component in the safety system is
explained below.
Thermocouple
The thermocouple is a device that generates
electricity when heat is applied to the tip.
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 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 3.4a
Figure 3.4b
Thermocouple
Gas flow
Electromagnet
Plunger
Shaft
Knob
Gas flow
Plunger
Insulator
Nut
Conductor
Tip
Internal
Wire
