There shouldn't be any switching either, they should all be connected with non-return Tee's so the all empty equally but can't backfill. It might be worth a bit of a replumb......
Agreed. Sometimes on engines that need a lot of gas flow and multiple tanks are installed, when a tank is empty (and we might expect the other tanks then to be at higher pressure than the empty tank so continue to flow liquid gas to the engine), what can actually happen is that the full tank does initially begin to fuel the engine but then it's temperature drops (due to fuel take-off at a high rate the gas in the tank has to evaporate to maintain pressure thus cools the tank) so the empty tank then becomes then one with the higher pressure... In certain cases the empty tank then pushes an airlock (gaslock) to the reducer, which requires liquid gas not vapour. Where the full tank has more pressure than the empty tank, fuel can flow from the full tank to the empty tank.. the tank valve and piping have a limit to what they can flow, so with enough flow from a full tank to an empty tank there isn't much flow rate remaining to fuel the engine, so again the reducer can receive vapour instead of liquid. If all new pipes etc are to be fitted would suggest using 8mm pipe and fittings.
However, if it has previously been OK as is, this could point to a developing reducer problem (needs more pressure at the input than it used to - inlet jet). Or, if one way valves are already fitted they could be faulty (the ball bearing in them can get stuck).
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