deisel tanks, fuel supply must be on top? is that right?

[steve yates]

Just read some bumf on a seaflow deisel tank, thro asapsupplies, and it says... "The fuel supply, fuel return, fuel fill and fuel breather pipes are all located on the top of the fuel tank, as required by ISO standards."

So the tank I am replacing has the fuel line coming out of not quite the bottom of the tank, so obviously gravity helps it on it's way.

Is this not normal anymore? Is this not going to cause problems delivering the fuel to the engine?

Yours in ignorance....

 

[[70521]]

My 30+ year old boat has all the pipework coming out of the top of the tank.

 

[pvb]

Having all the connections on the top of the tank is sensible in terms of reducing the possibility of leaks.

Gravity makes no difference - once the fuel pipe is primed, the difference in head between the engine and the surface of the fuel in the tank is the same.

 

[Robin]

Having all the connections on the top of the tank is sensible in terms of reducing the possibility of leaks.

Gravity makes no difference - once the fuel pipe is primed, the difference in head between the engine and the surface of the fuel in the tank is the same.

+1 The definitive answer. It also allows the fuel to be extracted from above the very bottom layer of sludge since there would probably be an internal tube pick up from the top inlet that stops just short of total bottom.

 

[RichardS]

Just read some bumf on a seaflow deisel tank, thro asapsupplies, and it says... "The fuel supply, fuel return, fuel fill and fuel breather pipes are all located on the top of the fuel tank, as required by ISO standards."

So the tank I am replacing has the fuel line coming out of not quite the bottom of the tank, so obviously gravity helps it on it's way.

Is this not normal anymore? Is this not going to cause problems delivering the fuel to the engine?

Yours in ignorance....

Don't forget that the fuel supply line still goes to the bottom of the tank even though it exits through the top ..... so, as PVB says, the gravity head is the same as a bottom exit.

Richard

 

[steve yates]

Brilliant, thanks all. Now it’s clear.

 

[NormanS]

Gravity as we used to know it, has been banned by some sort of 'elf and safety mechanism. That's why you see people using an electric windlass to push their anchor down to the seabed
Fortunately, I and a few other old diehards, have found a way round this ruling, and our diesel happily reaches our engines through pipework from (near) the bottom of our fuel tanks, and our anchor chains rattle out at speed, merely controlled by a brake

 

[pcatterall]

Nice to have drain at the very bottom though?

 

[pvb]

Nice to have drain at the very bottom though?

Ideally, but this can still be effectively achieved by a separate dip tube from the top.

 

[Topcat47]

My installation is 50 years old and the pipe exits from the bottom of the tank. If you have a top mounted pipe and you run dry, there is a guarantee that there will be an airlock in the pipework which will be a B@$$£r to eliminate when trying to bleed the engine.

 

[NormanS]

Ideally, but this can still be effectively achieved by a separate dip tube from the top.

Not nearly as good as having a small dirt sump with drain valve. Instead of water or dirt sliding about the bottom of the tank, it automatically drops into the sump, where it can't do any harm, and is removed by occasional draining.

 

[pvb]

Not nearly as good as having a small dirt sump with drain valve. Instead of water or dirt sliding about the bottom of the tank, it automatically drops into the sump, where it can't do any harm, and is removed by occasional draining.

All depends how accessible the tank is. My last boat had a keel tank, and had a separate dip tube and hand pump to suck rubbish out of the bottom of the tank.

 

[pvb]

My installation is 50 years old and the pipe exits from the bottom of the tank. If you have a top mounted pipe and you run dry, there is a guarantee that there will be an airlock in the pipework which will be a B@$$£r to eliminate when trying to bleed the engine.

If you run dry with any sort of pipe, there's an air lock. I've never found it that difficult to bleed it though.

 

[davidmh]

I advantage of the tank exit being near the bottom of the tank is that if there is a small leak on the in the pipe from the tank to the pump it will leak rather than have air sucked into the pipe and causing air to get into the injectors. I am sure the reason behind the rules is so that if the pipe in the line from tank breaks then the fuel spills into the bilge. With the pipe at the bottom of the tank you need to fit a stop valve at the tank.

Regards

David MH

 

[pvb]

I advantage of the tank exit being near the bottom of the tank is that if there is a small leak on the in the pipe from the tank to the pump it will leak rather than have air sucked into the pipe and causing air to get into the injectors.

I don't see any advantage in having a leaky pipe!

 

[prv]

Not nearly as good as having a small dirt sump with drain valve. Instead of water or dirt sliding about the bottom of the tank, it automatically drops into the sump, where it can't do any harm, and is removed by occasional draining.

The sump is good, if there's space for it (the tank isn't sitting directly on the bottom of the hull, for instance). But it can be drained pretty much as effectively by a dip tube descending into it from the top, as by a valve on the side.

Pete

 

[fisherman]

this sort of question goes round and round, my fuel level is higher than the injector pump when full tank so bleeding from the btm outlet is really easy. It was changed from top outlet by a previous owner, and I know of several boats where this has been done after air leaks have broken the syphon from a top outlet. But, if I get a leak it's up to 1000 litres in the bilge.
The best solution if it can be managed is a day tank. Hand or electric pump (or both) to fill it from the main tank. Even better would be incorporating fuel polishing, a constant flow of fuel via filters to the day tank with an overflow back to the main. My ideal day tank would be very tall and thin with a good sump and drain offs. Should the pump fail you still have a day tank full. It would also be possible to fill it from a can. All problems with air, sludge, priming etc disappear.

 

[LittleSister]

this sort of question goes round and round, my fuel level is higher than the injector pump when full tank so bleeding from the btm outlet is really easy. It was changed from top outlet by a previous owner, and I know of several boats where this has been done after air leaks have broken the syphon from a top outlet. But, if I get a leak it's up to 1000 litres in the bilge.

Surely the 1,000 litres will end up in the bilge regardless of whether the supply is taken via the top or the bottom of the tank?

In both cases the pick up is just above the bottom of the tank, and (if there's fuel coming out) the leak is below that.

 

[fisherman]

Surely the 1,000 litres will end up in the bilge regardless of whether the supply is taken via the top or the bottom of the tank?

In both cases the pick up is just above the bottom of the tank, and (if there's fuel coming out) the leak is below that.

Yes of course, only the leaks that stop the engine occur at the union on top of the tank would not fill the bilge.

 

[fisherman]

So, thinking more about a day tank, how easy would it be to install in, for instance, a cockpit side locker, or under an after deck? Filler, drain off and engine feed tap all to hand, and a good gravity feed, no bleeding of the pumped feed from the main tank needed.