I have a 10kw propane generator fed by two 500 gallon above ground tanks. The tank feed lines are tied together with a tee. I usually use one tank at a time, switching over and calling the supply company when one gets low. I decided to use both tanks at the same time reasoning I would have to have the company out half as often. The takes have about 275 and 400 gallons respectively. After I opened both values feeding the single line to the house and generator, the generator refused to run. It would crank and shut down after about 10 seconds. This happened over and over. The hot water heater and stove worked fine. The generator is designed to shut down if the oil pressure is too low but that is the only shut down safety precaution I am aware of and not other in documented. I then thought it might have something to do with using dual tanks. I shut down the fuller of the two and sure enough the generator starts up and runs just fine. My question is: Why? What is going on when the two tanks are being used that lowers the gas pressure so low it will not allow the generator to run?