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Old 10 April 2006, 05:25   #1
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Fuel tank breather

I seem to have a problem on my RIB with the fuel tank leaking at the top when it is full or nearly full. I spent a nervous period yesterday with about half a pint of spilled petrol and a battery between my legs and decided it needs sorting before I have an involuntary thermic castration (not to mention maybe having to swim home!)

The tank appears to be sealed with no separate breather (though I can't see the front of it) and the filler cap seals with a cork gasket, so I assume it's coming out the breather widget, which is a thing on top of the tank cap. After I mopped the mess up when I came back in I had a fiddle and the breather is a sort of screw in thing with a tiny notch in the side of the thread, that was unscrewed about 2 turns (which was how it was when I got it from the previous owner). I screwed it right in tight which I hope will stop the leak (and violently rocking the boat from side to side didn't produce any fuel), but I guess it will also stop any air getting in.... though I haven't been anywhere yet and it is tipping with rain today so probably won't be!

So I wondered about a remote breather - bit of plastic tubing or something - that would go on to the cap and vent a bit higher up - I think the fuel is "slopping" in the tank and coming out the breather.

What breather arrangement does everybody use? Or if you use a thing like the above arrangement, do you just tighten it and crack it off a fraction of a turn?

Of course I could just not fill the tank right up but it disappears fast enough as it is without running it half empty

Thanks

Stephen
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Old 10 April 2006, 05:33   #2
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I have a seperate breather take off from the tank which attaches to a long piece of pipe that coils around once and terminates high in my console. I've never had a problem with this setup. I think this is a quite common arrangment on RIB's.
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Old 10 April 2006, 05:43   #3
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Thanks ... I suppose mine might have the same thing but fitted at the front of the tank (you can't see that as it is under the console) and maybe the breather thing on top of the cap is supposed to be kept tightly closed?

Does anybody else with a Humber Destroyer (or in fact probably any sort of Humber - chances are they would all use the same arrangement) with an underseat tank, know the answer? I don't think I could get at the front of the tank to be able to check, without taking the console off the deck.

I was thinking of a similar idea, a fitting on top of the tank, something like windscreen washer tubing running up to a small inline filter mounted a few inches above the tank, this way if a small amount did get up into the filter it would drain back down in next time the air in the tank contracted, rather than blowing out the top, and the filter would also stop any muck getting in.
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Old 10 April 2006, 06:34   #4
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I am just redesigning my console with a new fuel tank built in and I have decided to have a remote vent as well but using a console mounted vent, see picture, available from tek-tanks.com for about 7.

As I understand the vent is for both directions, pressure build up due to temp change and also inlet vent for when using fuel. I was relunctant to put the vent inside as I thought fumes could build up, and being in close to the electrics.... . I may be wrong on this, can anyone elaborate?

I am going to locate the external vent in a place that should be splashed in a minimum way. Hose length will be about 24 inches with loop in the middle.
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Old 10 April 2006, 06:38   #5
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Humber

I also have a destroyer with your console as well and to be really sad have your sunset picture as my desktop background !

The tank in mine has a simple vent on top which will let a little petrol out when very full or hot , I have no means of venting elswhere without making another hole . I think plenty of ventilation is the answer .
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Old 10 April 2006, 07:41   #6
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Quote:
Originally Posted by Narcosis
I was relunctant to put the vent inside as I thought fumes could build up, and being in close to the electrics.... . I may be wrong on this, can anyone elaborate?
I've got the same concern ... I'm rather attached to the bits of me that would bear the full force of the explosion and while the only connections in that compartment are battery, fuel gauge and the isolator, it also has holes through into the front compartment where all the electrics are ....

that external vent sounds like a very good idea ... after all it would only take a loose battery connection or something, one good spark and boom, suddenly you're into aviation in a big way... though I have to say, once I mopped the mess up and left it with the seat off to vent for a while, you couldn't really smell fuel in the underseat compartment, and when the engine is running presumably you'd not be venting fumes because the tank will need to draw in air to replace the fuel. At all other times I leave the master isolator (also in that compartment) firmly off, so there shouldn't be a problem apart from when I am using the thing.

On a simpler level, another idea that occurred to me just now would be to run a vent up to the rear of the console, then make a little U-bend out of some small diameter pipe (copper brake pipe is what I had in mind) drill a small hole in the back and feed the U-bend out through, so the open end was pointing downwards, it should be well protected from any spray in that position and would mean all the nasty little airborne petrols would be dispersed out into the air.

Lurcher, so have I
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Old 10 April 2006, 08:05   #7
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Quote:
Originally Posted by BogMonster
while the only connections in that compartment are battery, fuel gauge and the isolator, it also has holes through into the front compartment where all the electrics are ....
you will be telling us next that the battery cables and the petrol fuel line are fed down the same trunking either across the deck or underneath it.

Most petrol tanks vent to the outside of a console terminating in a flame proof fitting like Narcosis pictured. Petrol vapour is heavier than air, if the tank is leaking petrol its also filling your console up with petrol vapour.

This is a pm Claus sent last year:

Sad news.....She blow up last week. I had orderes a guy to weld on the fueltank, and it blow up...he spend 4 days in the hospital and the next 12 weeks with his arm i bandages. I was almost finish with her after spending more than 200 hours rebuilding her this winther...and she blow up 2 days before entering the sea...(So sad...I cryed for a week.) Im trying to get the insurance company to rebuild her, and therefore i needed the hull year.

I think you need to get the petrol and electrics well separated in different compartments and the fuel tank area well vented.

Pete
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Old 10 April 2006, 08:44   #8
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I guess so then - there is only one bundle of cables and things going to the motor, though it isn't in trunking, it just comes out a big conduit, goes across the deck and down one side.

I assume the whole layout is as Humber (or Oakley Marine who I believe supplied the whole thing) built it - the engine was supplied with the boat when new and I am fairly sure neither of the previous owners would have interfered with anything fundamental while they had it. That suggests that it is built the way that they build all of their boats, which in a way I guess is a bit worrying!

It doesn't strike me as a good or safe design either - but as there's nowhere else to put anything, I'm not sure what the options are really. Believe me I ain't too happy about sitting on it though - hence the original question!
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Old 10 April 2006, 08:54   #9
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If the cables go though a bulkhead in the console to the front then some witches hats and sealant would be better stops the wires fretting on the grp too, fit another to the throttle control box where the wires go into the console. Finally how about some ply and glass at the back of the console to separate the fuel from the battery. Post some pics and see what we can come up with.

Pete
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Old 10 April 2006, 09:11   #10
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Is it too obvious to say that you shouldn't fill it quite so full???
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Old 10 April 2006, 09:46   #11
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Quote:
Originally Posted by codprawn
Is it too obvious to say that you shouldn't fill it quite so full???
Yes anyway the breather seems to leak even when it isn't right full, fuel slops around a fair bit when you are bouncing across the South Atlantic

Plus it is still venting into the battery compartment, which I am still not happy about and the more I think about it the less happy I get, in fact I can't believe I didn't go "aaaagh" when I first saw it.

When I get a second seat installed (awaiting a reply/fright from Humber on the cost) I'll have another compartment to play with and I think the battery and isolator might get relocated to that as I would be a lot happier if they were separate from the tank! I have been thinking about it this morning and I figure I can make up and fit a remote breather next weekend using a brake bleed screw threaded into the top of the tank, a length of flexible pipe and a "BT special" vent going out the back of the console, which has got to be an improvement. That way I can seal the tank cap completely and it will stop the leak.

I'll go down later and take some pics, assuming it stops raining cats, dogs, elephant seals, chickens, giraffes, penguins, hyenas and wild boar (its raining quite hard ... way past just cats and dogs) and post them later.

Thanks
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Old 10 April 2006, 09:49   #12
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I wouldn't like it venting into the console either. On my boat the rear tank breather comes out of one of the seats and the front one comes out of the side of the console.

Remember to make your breather big enough and make sure it doesn't get kinked or you will soon be stranded.

It is suprising how many breakdowns are caused by breather problems.
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Old 10 April 2006, 10:12   #13
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I have just been getting together bits I need (benefits of working in a place selling LR parts ) and it is only going to be about a foot long anyway so should be OK - basically a modded Defender brake caliper bleed screw into the top of the tank, a few inches of plastic tube, an inline filter attached to the inside of the console, then more plastic tube up to a vent out the back of the console pointing downwards so as not to let any water in.

KISS (I hope)

photos to follow
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Old 10 April 2006, 10:13   #14
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You must be a mind reader - was just going to suggest Land Rover parts - just been extending the axle and tank breathers on mine!!!
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Old 10 April 2006, 11:25   #15
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Quote:
Originally Posted by BogMonster
...Plus it is still venting into the battery compartment, which I am still not happy about...
Och, aye wundnae wurrie too much, the battery is venting hydrogen into there anyway.
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Old 10 April 2006, 11:28   #16
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OK

100 lines for me

I am a pillock
I am a pillock
I am a pillock
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[snip]

I have been around EFI systems too long....

I went back for a look at lunchtime, and pump all the rainwater out (they should put this thing in the middle of the Sahara, the place would be green by a week on Thursday, it collects so much rainwater...)

I looked at the plumbing yesterday, yep, two pipes coming out the tank unit, yep, that'll be the feed and return then, no breather to be seen.

Er

no

Fuel feed to motor and large bore breather pipe...

....which has a rather large kink in it at one point....

....right in full view.

Doh!!!

If I had bothered to look properly rather than peering stupidly at the source of the leak I would have noticed that the second pipe takes off towards the sharp end, not the end with the engine on, and ends on a vent thing high up on the front of the console!

10/10 to Mr Prawn then and 0/10 for me

There is no way it could be on there and not have a kink in so I think the tank unit needs to come out and be rotated about 45 degrees - as it is at the moment, the pipe is hard against the side of the console which is why it has a kink in it. Dodgy assembly I guess!

Thanks for the input and sorry I have been a complete muppet....
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Old 10 April 2006, 12:19   #17
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At least you found it, but please do vent it outside with one of those nice fittings.

Pete
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Old 10 April 2006, 12:44   #18
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Not trying to hijack the thread, but:
Quote:
Sad news.....She blow up last week. I had orderes a guy to weld on the fueltank, and it blow up...he spend 4 days in the hospital and the next 12 weeks with his arm i bandages.
What kind of welder would work on a fuel tank without emptying, flushing with water, and leaving it full of water (I'm pretty sure that's standard practice on that one.) Certainly not with any way of fumes remaining inside (or worse yet, gas...)

jky
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Old 10 April 2006, 13:26   #19
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Good question, I used to watch the welders leave a hose pipe in a tank over night before emptying. This was a stainless steel tank glassed in but I put a 6 inch inspection hatch in with bolts so he didn't even bother to take this out and clean out the tank.

Pete
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Old 14 April 2006, 14:07   #20
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All sorted now

the problem was in fact the kinked breather pipe leaking, not because it was kinked (nothing I can do about that, a large bore pipe with no room for a natural curve but it still lets plenty of air through when you blow through it) but had gone "hard" at the end going on to the tank and just wasn't sealing. Bit of vaseline, pushed it on harder and a jubilee clip to make sure it was a tight fit, and it is fine. It breathes out through a fitting on the front of the console, which has a fine gauze filter in it as in the attached pic. I wanted to turn the tank unit round but can't because of the way the fuel sender is installed.

I think everything is fuel and air tight now because I took the breather outlet off, blew down the pipe to pressurise the tank then put my thumb over it for a while, and when I released it there was still pressure in the tank so hopefully no more leaks nasty smell of petrol has all but gone from the inside of the console too, and having been away and bounced over a few waves this afternoon it is all nice and dry under there so hopefully the crown jewels are safer now
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