Update--I am saved! DW is persuaded to leave the big tank on with the appliances all off, now we know about the big tank having that safety shut off. AFAIK, the 5er didn't have that for its twin 30 lbers.
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OK I get the picture. Interesting!
Yes our procedure is to turn all appliances to OFF and turn off the tanks, then turn tanks on and run the appliances. Sometimes there is a brief wait for the fridge to get gas--we turn on the stove first to confirm gas has arrived-- but nothing like what this rig seems to do.
Good explanation of "demand" for each appliance, thanks. I did think that if the stove had gas that meant there was gas to the fridge too. Now I see it is trickier than that.