There's no point in having a non-return valve in the return line at the lowest point of the system! What is it going to do? Stop fuel flowing uphill, against the designed flow direction? Also it doesn't matter if the return line is empty. If there is one there, it doesn't serve any useful function, unlike the one between the filter and the tandem pump on a Lupo 3L.
RAB
I know what you are saying...but it has
)...i don't doubt you logic.
But in my case...for my 1.2 tdi from 2001 there is a return valve on the return line in the fuel tank (I hope I expressed the position corectly).
I started to test the system bit by bit because i had lots of air coming into the tandem pump input line.
Anyhow...i think i discovered my culprit.
The valve that is on the fuel filter. I tried to absorbe fuel right after the filter with a manual pump aaaand no luck.
The filter would not fill up(Does it have to be full when installing?...i do not remember doing this last time).
Any ideea what 057127247A valve is doing (the T valve that is mounted on top of the metalic fuel filter)? (as far as i know it should warm up fuel in the filter from the return line?..something like this?).
I just noticed a small crack in it...and if i try to push air trough it it seems to be very locked (and it does not matter if i press air from one side or the other even if it has an arrow on top regarding sense)
And by the way cyril explaind his symptoms....this might be the culprit in his case too. I tried presurizing the fuel tank with an air compressor and it worked for a bit. I will keep you informed if changing this stupid valve solves the priming issue.
@Cyril13013 any ideea what type of fuel filter you have? Did you change 057127247A on your filter?
@RAB this thing looks like it can act as another return valve....and again is on the return line....almost at the end. Not sure if it does...i will test on the new piece