Originally Posted by roach711
That's probably the safety gas shutoff valve for the oven.
X2 on that. But I would suspect the tube going to sense the pilot light, at least the one in the picture, uses mercury or another liquid to shut off the gas with a mechanical, not electrical action if the pilot goes cold.
Check around for stove burner specifications. I think our home stove has four 9000 BTU units. I have seen others which have a couple of really high output ones and a couple of medium output ones. Our burners are a little slow for canning or cooking big pots of soup, but even 4000 BTU should be usable for light cooking if you have the right regulator pressure setting.
Gas pressure at appliances is generally measured in water column inches, or how high the pressure can lift water in a tube. If I recall correctly, about 7 inches equals one PSI. A big generator uses 14" (2 psi) or less, I would expect the internal regulator on home appliances to be between 0.5 and 1.0 PSI previously stated.
Natural gas utilities tell me city gas pipes run about 70 PSI. Propane tank pressures run much higher. Propane boils into vapor at about -44°, but remains liquid because the tank is sealed and the vapor pressure rises. It is just like a car or truck radiator pressure cap keeping water as liquid and not steam above 212°F (100°C) because it has nowhere to go. The pressure in a propane tank depends on the outside temperature, the rate vapor (if any) is being drawn from the tank, and the amount of liquid surface area that can boil off the needed vapor. The 250 PSI is likely sitting in the hot summer sun, an average tank pressure is probably half that on a day-to-day basis.
Two-stage schemes can be separate regulators, or an integrated two-chamber unit. My guess is that the integrated two-chamber unit is better able to give a steady appliance low pressure from a high pressure tank than trying to do it in a single chamber.
There is another scheme, where the regulator at the tank is set for a medium pressure, usually about 70" (10 PSI). This is higher than needed by the appliances, in order for the extra pressure to overcome the friction restricting flow in the supply pipes. The second regulator is placed at the point of use at the appliances.
The split system is great for standby generators, as it avoids fuel starvation from a pressure drop if the load suddenly increases. I have seen generators that start and run fine, and then choke and sputter if a heavy load comes on and the gas pressure can't recover. I would expect the same, but less dramatic, as a gas oven control cycles the burners on and off.
If the low-pressure regulator were back at the tank, it would take a while for it to see the drop and adjust the pressure to the line. But if there is medium pressure in the line 5 times what is required, the regulator at the point of use can quickly adjust to the need without having to change the pressure in the entire line.