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This week I was wondering how long it would take a pilot light to deplete a tank of LP fuel (the kind people use for grilling.) Several months? A year? For n

This week I was wondering how long it would take a pilot light to deplete a tank of LP fuel (the kind people use for grilling.) Several months? A year? For no particular reason, I wondered what the limitations would be on shrinking the pilot light. Could a small tank keep a flame going for 10 years? 100 years? I sense one challenge would be machining a small scale nozzle for laminar flow, and carefully filtering both fuel and air inputs to ensure the tiny nozzle didn't clog, for instance, with a grain of sand, or a piece of pollen. At a small scale, what are the limits of flame? This article scratched an itch.

amluto 6mo ago
A pilot light is tricky: in typical designs, it needs to heat a thermocouple enough to produce enough current to drive a solenoid to allow the rest of the flame to ignite. Thermocouples are outrageously inefficient.
- NetMageSCW 6mo ago
  The pilot lights I’m familiar with just light the rest of the flame directly since they are burning already - turning on the fuel is all that is required. What systems uses a thermocouple and a solenoid?
  - bob1029 6mo ago
    I've got a Honeywell digital controller on my hot water heater. It's powered by the thermocouple. It can make troubleshooting a lot easier because it has flashing lights for diagnostics.
  - amluto 6mo ago
    It’s extremely common for the mechanism that only allows the fuel to be turned on if the pilot is lit to work by having a thermocouple in the pilot flame. Some of these also power the controls (thermostat, for example) and some don’t.
    - throwway120385 6mo ago
      Yeah blowing yourself up with a gas leak is common enough when you're working on these systems that it's pretty important to have an interlock there.
  - compiler-guy 6mo ago
    Approximately all gas appliance pilot lights. https://www.acservicetech.com/post/how-the-gas-pilot-light-functions-and-10-reasons-why-the-pilot-light-goes-out-or-won-t-stay-lit https://www.acservicetech.com/post/how-the-gas-pilot-light-f...
  - dghlsakjg 6mo ago
    Any modern country with safety regulations will require a thermocouple in the loop if there is a pilot light on the appliance. The last non thermocouple appliance I saw was an industrial kitchen stove, but it had been modified for propane, and I suspect that the guy who did it ripped out the safety stuff. Every factory appliance will gate the full gas flow behind the activation of a the thermocouple. When you push and hold a dial or button to get a pilot lit, what you are actually doing is bypassing the thermocouple safety until it gets to temperature. If you release the “hold to light” knob too soon your pilot will go out since the thermocouple needs ~10 seconds to get to temp.
    - amluto 6mo ago
      The only commercial kitchen stove I interact with on a somewhat regular basis is a miserable piece of crap. It has multiple pilot lights, some of which go out frequently and stink up half the building with unburnt fuel. I suspect that just the pilot lights consume $50-$100/month of natural gas. Stoves seem to be somehow special in safety regulations. I guess regulators assume that they are never operated unattended, so they tend to have no real built in safety features. Both commercial and residential stoves will happily operate unlit at full power.

amluto 6mo ago

A pilot light is tricky: in typical designs, it needs to heat a thermocouple enough to produce enough current to drive a solenoid to allow the rest of the flame to ignite. Thermocouples are outrageously inefficient.

NetMageSCW 6mo ago
The pilot lights I’m familiar with just light the rest of the flame directly since they are burning already - turning on the fuel is all that is required. What systems uses a thermocouple and a solenoid?
- bob1029 6mo ago
  I've got a Honeywell digital controller on my hot water heater. It's powered by the thermocouple. It can make troubleshooting a lot easier because it has flashing lights for diagnostics.
- amluto 6mo ago
  It’s extremely common for the mechanism that only allows the fuel to be turned on if the pilot is lit to work by having a thermocouple in the pilot flame. Some of these also power the controls (thermostat, for example) and some don’t.
  - throwway120385 6mo ago
    Yeah blowing yourself up with a gas leak is common enough when you're working on these systems that it's pretty important to have an interlock there.
- compiler-guy 6mo ago
  Approximately all gas appliance pilot lights. https://www.acservicetech.com/post/how-the-gas-pilot-light-functions-and-10-reasons-why-the-pilot-light-goes-out-or-won-t-stay-lit https://www.acservicetech.com/post/how-the-gas-pilot-light-f...
- dghlsakjg 6mo ago
  Any modern country with safety regulations will require a thermocouple in the loop if there is a pilot light on the appliance. The last non thermocouple appliance I saw was an industrial kitchen stove, but it had been modified for propane, and I suspect that the guy who did it ripped out the safety stuff. Every factory appliance will gate the full gas flow behind the activation of a the thermocouple. When you push and hold a dial or button to get a pilot lit, what you are actually doing is bypassing the thermocouple safety until it gets to temperature. If you release the “hold to light” knob too soon your pilot will go out since the thermocouple needs ~10 seconds to get to temp.
  - amluto 6mo ago
    The only commercial kitchen stove I interact with on a somewhat regular basis is a miserable piece of crap. It has multiple pilot lights, some of which go out frequently and stink up half the building with unburnt fuel. I suspect that just the pilot lights consume $50-$100/month of natural gas. Stoves seem to be somehow special in safety regulations. I guess regulators assume that they are never operated unattended, so they tend to have no real built in safety features. Both commercial and residential stoves will happily operate unlit at full power.