Fuel tank quandry

[Gordonmc]

Anyone out there able to fill me in about the normal feed arrangement of twin diesel tanks?
I noticed on filling the st'bd tank that the port one stayed at about a third full. The weekend brought great weather in Scotland so I filled both tanks in the expectation the donkey would be doing most of the work. Back at the berth the port tank was still full, the st'bd about half.
I checked the small taps on the bottom of the tanks and both seem to be "on". The taps attach to piped which T together just before the water seperator.
The only thing I can come up with is that the port tank tap itself is blocked, possible by rust as they are mild steel.
Before I go through the drudge of draining the tank, any ideas?

 

[Gaffer]

It could be that the port tank is not venting.
By the way, we were at the Boat Jumble at Irvine on Sunday, and had a most enjoyable day. The weather was glorious and the atmosphere was excellent. Well worth the trip from Southampton.

 

[Guest]

Used a boat which had two diesel tanks. Each tank was filled independantly. The engine drew fuel from both tanks simultaneuosly, although the fuel taps could be set to make it use one tank at a time. All of the unused fuel which returned to the tank from the engine went into the port tank, so this tank was always more full than the other one.

 

[vyv_cox]

Disconnect the pipework downstream of each closed valve. Attach a length of plastic tubing long enough to reach the fuel level and open the valve. This will show you if there is a blockage inside the tank. If so, blow some air down the tubing and through the tank after opening the valve. This may clear the blockage but probably indicates that there is something inside that needs investigation. It could well be rust, I have had this problem in the past, where large rust flakes covered the tubing end. Alternatively, strong chance that you have black sludge inside. (Cue for Soltron advertisement - Dom?)

If no blockage, try blowing through the fuel pipes from the separator end to find/clear the blocked one.

 

[brian_neale]

Years back I chartered a boat with a Stuart Turner two-stroke, centrifugal clutch and no reverse. It developed the habit of cutting out at strategic moments (like in the path of the Dartmouth chain ferry), but could be restarted after topping up the fuel tank - even though it was not short of fuel. The owner changed the filter, generally tinkered around, and at my insistence eventually took out the fuel tank for investigation. There was a crisp packet floating around in it...

Hence refuelling working - it disturbed the blockage temporarily. Maybe a problem unique to boats spending much time alongside public quays, but the moral is that if you can clear the blockage by blowing back up the feed line, as sure as eggs is eggs it is going to block again, and always at an awkward moment!