Moffat BLUE EVOLUTION G91, Руководство по обслуживанию

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3
Operation
13
Blue Seal Evolution Series Gas Salamander © Copyright Moffat Ltd. 9 February 2016
Amendment 9
3.4 Explanation of Control System
Safety System
The purpose of the safety system is to shut off the flow of gas if
the burner flame goes out. It comprises of the flame itself, the
thermocouple, and the flame failure gas valve.
The burner flame is lit by holding 'In' the gas control knob,
which in turn temporarily pushes 'Open' the plunger inside the
safety valve 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.
The tip of the thermocouple is located in the 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 burner 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.
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 are 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.
Figure 3.4a
Figure 3.4b
Thermocouple
Gas flow
Electromagnet
Plunger
Shaft
Knob
Gas flow
Plunger
Insulator Nut Conductor Tip
Internal
Wire