Generator propane feed

[Barefoot Bill]

The 2010 3400RL that we acquired last summer has an Onan 6500 generator using propane. I hadn't tried running it until a power outage at RV park on July 4 (record high temps in Alaska) and couldn't get it to start. Took it to the Cummins service center in Anchorage a couple days ago.

For $81, I learned something that some of you probably could have told me. Generator won't run with door-side (side without main pressure regulator) propane tank turned off. Technician thought that was because the other tank was empty, but it wasn't. So, I infer that the propane feed to the generator is from a tap on the crossover pipe. So, if the regulator switch is turned to the same side tank and the other (door-side) tank valve is closed, there's no propane in the crossover pipe. Can anyone confirm or offer another explanation?

I'm in the habit of only having one tank on, so I will know when that tank is empty without checking the regulator for the red flag and risk emptying both tanks before I notice.

[jetskier]

There is no tee in the crossover pipe. The crossover pipe isn't at the right pressure for the Onan to run (too high). The secondary regulator drops the tank pressure a bit, but not to the 1/2" WC the main regulator does.. It's a flow problem through the regulators. I had to replace the regulators on my old trailer cause I had a similar issue where it wouldn't run on the tank on the opposite side of the main regulator. The Onan units need a steady flow of propane to run.

[PNW Fireguy]

We have the same issue but on regulator side. Ours is because it was easiest to install on a single bottle rather than re do the piping with a T.

[Barefoot Bill]

OK, so now I'm thinking it was just because only one tank was turned on and it was close to empty, so perhaps the regulator couldn't maintain the pressure that the generator required. That may also explain why the water heater sometimes won't start on gas. I guess I'll have to make a practice of turning both tanks on.