How does a gas valve work without power?
#1
How does a gas valve work without power?
At my cottage I have a new NG water heater. It's a standard vent model with standing pilot but has the enclosed base now required. My question is how does the gas valve operate with no external power source? It even has a flashing LED to indicate the pilot is lit.
I don't understand how the few mv generated by a thermocouple can open the gas valve, much less light an LED.
I don't understand how the few mv generated by a thermocouple can open the gas valve, much less light an LED.
#2
Member
Although a thermocouple doesn't generate much voltage with a single junction, it can generate a fair amount of current. The current is enough to operate a sensitive electromagnet to open the gas valve. It is possible to use an electronic inverter circuit to generate a high enough voltage to operate an LED.
Alternately, a thermopile can be used, which has many thermocouples in series in order to generate a higher voltage.
Not sure which approach your particular WH uses.
Alternately, a thermopile can be used, which has many thermocouples in series in order to generate a higher voltage.
Not sure which approach your particular WH uses.
#3
It can be completely mechanical. A tubular probe extends inside the tank to sense the water temperature. The tube is filled with heat expanding liquid like a thermometer. But instead of having the liquid go up a glass tube extension with a numbered scale behind, the liquid pushes a diaphragm or lever that opens or closes the gas valve (or a spring could be used to push the valve the other way).
This technique is used in a variety of other applications, too, such as the zone valve for a heating system loop or the "thermostat" in a car engine that delays the flow of coolant to the radiator until after the engine reaches a certain temperature.
This technique is used in a variety of other applications, too, such as the zone valve for a heating system loop or the "thermostat" in a car engine that delays the flow of coolant to the radiator until after the engine reaches a certain temperature.
#4
Thanks Paul. I didn't know (or had forgotten) that a thermopile was several junctions in series.
I've never peeked in the "chamber" to see what might be in the flame. It's rather difficult with these new enclosed burners.
I've never peeked in the "chamber" to see what might be in the flame. It's rather difficult with these new enclosed burners.