Standpipes in a diesel tank

[Ian_Edwards]

I've been having problems with leaks from the top of a vetus "plastic" fuel tank for some time, so I'm considering getting rid of the circular connection plate supplied by Vetus, it's an old style system which relies on an "O" ring seal.

I plan to use a SS plate bolted into position with a gasket and sealant (not sure which one to use as yet). I'll put the bolts in from inside the tank, using large penny washers and using helicoil inserts, just to hold the machine screws in place, so that they look like a set of studs from above. I plan to make the bolt centres just a bit bigger than the diameter of the penny washer, so the plastic tank has a lot of internal support. This should enable me to pull the SS plate up against the tank and compress the gasket. The SS plate will have welded connection for fuel in, vent and fuel out.

The current arrangement tank has three standpipes, engine, generator and Eberspacher.

Is there any good reason why I can't use just one standpipe and a manifold arrangement to get the 3 fuel supplies?

I can see that it would mean all three would run out of fuel at the same time, but it's a 400L tank and I seldom run it to less than 50%, so there is usually plenty of fuel. If the standpipe ever gets blocked by debris in the tank, in the current arrangement the engine would get blocked 1st, since it has the longest standpipe.

I was thinking of using a single 10mm pipe and then 2 Tees and an Elbow to bring get to the 3 hose connects.

Is this a sensible way to proceed?

And, finally, what's the recommended clearance between the bottom of the tank and a standpipe?

 

[oldharry]

It might be an idea to take the 10mm feed pipe down outside to below the minimum level of the tank to reduce the number of connectors and therefore reduce the leak risk. Better still to give the lift pipe enough external length to take below the bottom tank level - no lchance of leaks then! I did that on mine, and have had no problems with it.

 

[lw395]

There is a potential issue with air leaking from any one of the diesel users making the others fail.
Also when bleeding, it requres the eber and generator pumps not to leak air under suction.
Whether that's a real enough issue to matter, I don't know.
You should probably have taps on the manifold anyway?

Personally I would put in another standpipe drawing from the very bottom of the tank for removing water etc. I'd put it at one corner and clean the tank with the boat heeled that way.

 

[Ian_Edwards]

I plan to put taps close to the tank for the generator and Eberspacher, which is what I have now, but the valves on the tank for the generator and Eberspacher are/will be under some upholstery and locker lids, so not that accessable.

The main fuel line to the engine has a fire shut off valve accessable from the companionway.

I have to admit that I don't understand oldharry's suggestions. The tank is sandwiched between the centreboard case and a water tank, and is hard against a bulkhead at the forward end, so running a pipe outside below the bottom of the tank, isn't practical. However, the fuel filter and lift pump on the engine are well below the fuel level in the tank when it's full, so that fuel will syphon out of the tank to fill the filters after a filter change.

I haven't had a problem with leakage from the any of the fuel lines, the leaks are between the plastic tank and the tank fitting.

I like the idea of an additional standpipe to remove water or debris from the bottom of the tank, I could use that with my fuel polishing kit a in the spring to ensure I start the season with clean fuel.

 

[fisherman]

If you made the hole in the tank square you could make a square backing plate with fixed studs or nuts or tapped holes. Not sure if it's worth it, but would give a good seal.

 

[lw395]

If you made the hole in the tank square you could make a square backing plate with fixed studs or nuts or tapped holes. Not sure if it's worth it, but would give a good seal.

Works well with tanks of unifrom thickness.
Beware that the Vetus tank might be thicker around the original fittings?
This may give trouble getting the gasket to seal.
Backing plate in two halves ('c' shaped) is one approach.

 

[PaulRainbow]

Regarding the tee's at the standpipe.... my Eberspacher installation manual advises that it can be fed by a tee at the tank, the tee should be as close to the tank as practical. Another option is to connect the Eberspacher and generator to the fuel filters, if they have multiple outlets, this is how my Eberspacher is connected, with an isolator valve where it connects to the filter (CAV filter housing).

 

[PaulRainbow]

Works well with tanks of unifrom thickness.
Beware that the Vetus tank might be thicker around the original fittings?
This may give trouble getting the gasket to seal.
Backing plate in two halves ('c' shaped) is one approach.

That would be my approach. C shaped plates with either studs or nuts welded in place and stuck inside the tank with a good bead of suitable sealant. I wouldn't mess around with helicoils.

 

[Ian_Edwards]

I've considered a backing plate of some form and welding set screws, to form studs.
My concern is how do you hold it in place when you install it, and perhaps more to the point, when it I must remove it at some point in the future.
A good bead of sealant is one approach, but I've yet to find something which sticks to a Vetus plastic tank in, the presence of diesel, as I've found out trying to seal the tank, over multiple attempts, over the last 2 years.
Although helicoils are fiddly to insert, they are mechanical and won't drop out. I could replace the penny washers with one or more backing plate(s), but I'm unsure if that would be an improvement over penny washers. The inside of the rotationally moulded tank isn't flat, a plate would bridge the high points, whilst penny washers will just aline with the adjacent surface.

 

[fisherman]

If your backing plate has tapped holes then a bit of string through two holes will pull it into place. If studs, then tapped holes and countersunk screws in the tank top. The countersinks will need to be deeper than the screw heads otherwise you might compress the plastic and the top will bear on the screw heads impeding compression.

 

[Ian_Edwards]

If your backing plate has tapped holes then a bit of string through two holes will pull it into place. If studs, then tapped holes and countersunk screws in the tank top. The countersinks will need to be deeper than the screw heads otherwise you might compress the plastic and the top will bear on the screw heads impeding compression.

Ok I can see how that would work, It would just need a couple (or so, depending on the geometry) of small counter sunk screws to hold the the backing plate permanently in place.

Thankyou, I'll try that, invaluable help!

 

[Birdseye]

There is a potential issue with air leaking from any one of the diesel users making the others fail.
Also when bleeding, it requres the eber and generator pumps not to leak air under suction.
Whether that's a real enough issue to matter, I don't know.
You should probably have taps on the manifold anyway?

Personally I would put in another standpipe drawing from the very bottom of the tank for removing water etc. I'd put it at one corner and clean the tank with the boat heeled that way.

lw395 talks sense. put two pipes in. One to clean the tank bottom and which goes right to the bottom and the feed pipe which sucks from maybe 15mm off the bottom. Feed pipe has three terminals each with its own ball valve.

 

[Ian_Edwards]

lw395 talks sense. put two pipes in. One to clean the tank bottom and which goes right to the bottom and the feed pipe which sucks from maybe 15mm off the bottom. Feed pipe has three terminals each with its own ball valve.

I've just order the fittings to do just that, I now need to measure up for the plate and standpipes. I'll then be able to complete the design and get the plate and standpipes fabricated.