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Old 11-22-2022, 04:38 PM
 
Location: NE Mississippi
23,003 posts, read 14,334,431 times
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I am replacing the thermocouple in an outdoor heater. The new one is on order, I got the old one out and so forth.


So I wondered exactly how they work. All the texts say the same thing ... "Two dissimilar metals generate a small amount of voltage when heated".... That's how they work. End of article.
But that doesn't tell me what I want to know!... Some thermocouples have a copper tube. Some (mine) has two wires that are attached to a threaded nut device. It's easy to replace and I can see how to do it.


My question is, "What happens to this small voltage that we all know is being generated? How does that small voltage being sent to a tiny threaded device keep the gas on? In other words what does that "tiny voltage" DO?"
No text seems to want to answer that question.... They all say, "It keeps the gas on". Oh yeah?... How?


Thanx
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Old 11-22-2022, 05:02 PM
 
98,644 posts, read 97,755,949 times
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The thermocouple screws into the gas valve ..the little current generated works a solenoid that makes and breaks a switch in the valve that allows power to flow to the main gas valve .

If the pilot light goes out the thermocouple won’t close the switch to allow the main gas valve to get power and open
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Old 11-22-2022, 11:23 PM
 
Location: Berkeley Neighborhood, Denver, CO USA
17,203 posts, read 27,323,933 times
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https://en.wikipedia.org/wiki/Thermocouple
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Old 11-23-2022, 08:17 AM
 
Location: Johns Creek, GA
16,660 posts, read 61,447,681 times
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So your question is-
What is the Seebeck effect?

…we’re talking just a few “milivolts” also- nothing earth-shattering!
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Old 11-23-2022, 11:20 AM
 
Location: Sunnybrook Farm
2,063 posts, read 872,169 times
Reputation: 6186
Quote:
Originally Posted by K'ledgeBldr View Post
So your question is-
What is the Seebeck effect?

…we’re talking just a few “milivolts” also- nothing earth-shattering!
No, I think the OP was asking for this answer:

"the little current generated works a solenoid that makes and breaks a switch in the valve that allows power to flow to the main gas valve ." which is kind of correct, if you edit as follows

the little current generated works a solenoid that opens and closes a valve in the safety valve assembly, that allows gas to flow to the pilot and main burner.

Once the TC's hot, the pilot will stay lit without you pressing the button, and the main burner will turn on and off by thermostat. If the gas pressure drops to a very low level, the pilot will go out, the TC will cool off, the gas valve will close (no current to hold it open), and then when the gas pressure comes back up, it won't fill your house with gas.

This is also why such gas appliances don't require any outside electricity to operate. The house I live in, which's been in the family since 1973, used to have floor furnaces with TC-driven safety valves and TC-driven tstats so even if there were a power failure for days in the winter, we stayed warm. That in conjunction with copper-line phones powered in a power outage from the big diesel generators in the basement of the Southwestern Bell switching center, meant a power outage was really no big deal. A few people even had Arkla-Servel gas fridges so they were REALLY independent of the power grid.
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Old 11-23-2022, 01:03 PM
 
Location: Johns Creek, GA
16,660 posts, read 61,447,681 times
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Quote:
Originally Posted by rabbit33 View Post
No, I think the OP was asking for this answer:

"the little current generated works a solenoid that makes and breaks a switch in the valve that allows power to flow to the main gas valve ."

Maybe you should read it again-
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Old 11-23-2022, 01:51 PM
 
22,295 posts, read 65,631,559 times
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Quote:
Originally Posted by rabbit33 View Post
No, I think the OP was asking for this answer:

"the little current generated works a solenoid that makes and breaks a switch in the valve that allows power to flow to the main gas valve ." which is kind of correct, if you edit as follows

the little current generated works a solenoid that opens and closes a valve in the safety valve assembly, that allows gas to flow to the pilot and main burner.

Once the TC's hot, the pilot will stay lit without you pressing the button, and the main burner will turn on and off by thermostat. If the gas pressure drops to a very low level, the pilot will go out, the TC will cool off, the gas valve will close (no current to hold it open), and then when the gas pressure comes back up, it won't fill your house with gas.

This is also why such gas appliances don't require any outside electricity to operate. The house I live in, which's been in the family since 1973, used to have floor furnaces with TC-driven safety valves and TC-driven tstats so even if there were a power failure for days in the winter, we stayed warm. That in conjunction with copper-line phones powered in a power outage from the big diesel generators in the basement of the Southwestern Bell switching center, meant a power outage was really no big deal. A few people even had Arkla-Servel gas fridges so they were REALLY independent of the power grid.
I am finding the search engine optimization on Google and Brave becoming increasingly single-minded and unhelpful. The floor furnace of that era likely had a bi-metal thermostatic switch that was NOT a thermocouple, but a purely mechanical device. The standing pilot may or may not have used a thermocouple as a safety feature.

I have a wall heater from the era. There is a push down button that must be physically held down to allow gas to initially flow in the pilot light gas line, and then another button that provides a piezo spark. The first button then must continue to be held for about 15 seconds to allow the thermostat bulb to register that the pilot is indeed on. (If the pilot goes out, the tiny amount of gas going to the pilot is cut off within about the same period of time.) Then, once that safety switch opens the main gas line, the second bi-metal thermostatic valve controls whether the gas flows or doesn't flow to the burner. The clicks of the bimetal valve are quite audible. The piezo igniter uses electricity created by the push onto the piezo crystal, but otherwise no electricity is involved.

ThermoCOUPLES either generate tiny amounts of electricity or have a changing resistance that are used in a switching circuit. The power generated, AFAIK, is insufficient to do much physical moving of a valve component. If a thermocouple is in the pilot gas circuit, as long as the pilot stays lit, more electricity may not be needed for continued operation.
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Old 11-23-2022, 03:17 PM
 
Location: Sunnybrook Farm
2,063 posts, read 872,169 times
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Quote:
Originally Posted by K'ledgeBldr View Post
Maybe you should read it again-
Maybe you should read my whole post where I corrected what you just quoted and amplified on it.
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Old 11-23-2022, 03:18 PM
 
Location: Sunnybrook Farm
2,063 posts, read 872,169 times
Reputation: 6186
Quote:
Originally Posted by harry chickpea View Post
I am finding the search engine optimization on Google and Brave becoming increasingly single-minded and unhelpful. The floor furnace of that era likely had a bi-metal thermostatic switch that was NOT a thermocouple, but a purely mechanical device. The standing pilot may or may not have used a thermocouple as a safety feature.

I have a wall heater from the era. There is a push down button that must be physically held down to allow gas to initially flow in the pilot light gas line, and then another button that provides a piezo spark. The first button then must continue to be held for about 15 seconds to allow the thermostat bulb to register that the pilot is indeed on. (If the pilot goes out, the tiny amount of gas going to the pilot is cut off within about the same period of time.) Then, once that safety switch opens the main gas line, the second bi-metal thermostatic valve controls whether the gas flows or doesn't flow to the burner. The clicks of the bimetal valve are quite audible. The piezo igniter uses electricity created by the push onto the piezo crystal, but otherwise no electricity is involved.

ThermoCOUPLES either generate tiny amounts of electricity or have a changing resistance that are used in a switching circuit. The power generated, AFAIK, is insufficient to do much physical moving of a valve component. If a thermocouple is in the pilot gas circuit, as long as the pilot stays lit, more electricity may not be needed for continued operation.
The floor furnaces in my house had tstats located on the wall some 10 feet away, linked by a wire. They worked off the small current generated by a TC.
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Old 11-25-2022, 08:10 AM
 
Location: NE Mississippi
23,003 posts, read 14,334,431 times
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Got it. Thanks, all
I never found a text that told me there was a switch inside the main gas valve. That's the part I was missing. Obviously, that switch, activated by the tiny voltage generated by the thermocouple, is another thing that could fail.
I don't know that they ever DO, but they could.
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