Propane tank issues (low pressure)

You need to find a point where you can check the pressure in the lines. I have w.c. gauges but you can make a manometer with about 3-4' of tygon tubing. Double it over, tape in together, put about 1' of water in it and viola, you have the gold standard for measuring w.c. I've done that several times when my gauges broke or I didn't trust them. The line pressure should stay up to ~9" when all the LP appliances are lit. That rarely happens but the pressure should stay up to 10" when about half (btus) the appliances are lit. I've dissected my old RV regulator before and it wasn't the best designed thing I ever saw. The pin that pushed the diaphragm open rested against the soft rubber disc and over time the pin sunk into the rubber and essentially reduced the out going pressure. I cut new Viton discs and put it back together and I'm still using that same 15 yr old reg. The red/green tank indicator isn't the best thing to judge line pressure by cuz it is going by the first stage pressure but it's still a sign that something isn't right. Very possibly what I said about the pin sinking into the rubber. Internally, each tank has it's own first stage reg and the changeover knob simply adjusts the lead tank reg to a higher setpoint than the lag tank. The lead tank has a higher setpoint so it keeps the lag tank reg from opening til the lead tank can't deliver and the lag tank reg opens to deliver pressure to the 2nd stage reg. There will be a test on this, later! Normally, that variation in first stage pressure doesn't affect the 2nd stage pressure too much but I wouldn't count on it. Also, I always take the tank connectors off the pigtails and neuter the over flow ball and spring and put the connector back on the pigtail. I don't deep fry turkeys under wooden decks or heat my house with a BBQ grill and I don't need that over flow POS to cause me grief! Craig