What should the normal millivolt reading be under load for a safety valve using a thermocouple?

The normal millivolt reading under load for a safety valve using a thermocouple typically falls within the range of 12 to 15 millivolts. This range indicates that the thermocouple is generating enough voltage from the heat it senses, which is critical for the proper functioning of the safety valve.

When the thermocouple is exposed to heat from the pilot flame, it generates a small voltage that is needed to keep the safety valve open. If the reading is below this range, it may indicate that the thermocouple is not functioning effectively or that there is a problem with the pilot flame, potentially leading to a shutdown of the gas supply for safety reasons. Therefore, readings within the 12 to 15 millivolts range reflect a healthy thermocouple under required load conditions, ensuring the valve operates as intended.

The other readings may either represent insufficient thermoelectric output or an extremely robust output that is not typically expected from standard operational conditions.