Air lock in fuel system

[Littledan]

Hi, I have a 1978 Sadler 25 sailing boat. Last year we had a new 14hp Beta Marine engine professionally fitted by a boatyard in Kinsale, Ireland. He wasn't happy with the existing fuel tank (corrosion) and so he fitted a new 30ltr plastic tank down low centre stern of the boat. We was bringing her in past the head, Kinsale under power because the wind had died and there was maybe 3 metre swells when the engine failed. We had a worrying time, because the engine refused to start, but when the engine was primed she started and performed well. Ya man at the boatyard said he thought the swell had swished the fuel in the 25% full tank causing the feed pipe to suck in air.

The original tank was fitted high to the stern starboard side and had a pipe from the bottom where as the new tank has a fuel feed pipe exiting the top of the tank. I can understand that that the old fuel tank would not have this problem but surely there must be a way to stop this happening with the new set up, otherwise you would see boats being tossed about out of control all over the shop.

Does anybody know how to stop this happening again?

 

[Stemar]

Apart from filling up when the fuel gets below about half, I don't know how to stop it happening, but a bulb pump in the system would simplify and speed up the bleeding process.

 

[Sandy]

Hello and welcome to the forum.

A few questions:

• Did the fitter talk to you about fitting a new tank;
• Did you agree to the work being done;
• Why did the fitter decide to fit the tank in the location s/he did?

Can the new tank be moved to the position of the old tank?

I've never heard of waves causing fuel to 'swish about' and cause air locks as the bottom of the fuel line is close to the bottom of the tank.

 

[Plum]

Hi, I have a 1978 Sadler 25 sailing boat. Last year we had a new 14hp Beta Marine engine professionally fitted by a boatyard in Kinsale, Ireland. He wasn't happy with the existing fuel tank (corrosion) and so he fitted a new 30ltr plastic tank down low centre stern of the boat. We was bringing her in past the head, Kinsale under power because the wind had died and there was maybe 3 metre swells when the engine failed. We had a worrying time, because the engine refused to start, but when the engine was primed she started and performed well. Ya man at the boatyard said he thought the swell had swished the fuel in the 25% full tank causing the feed pipe to suck in air.

The original tank was fitted high to the stern starboard side and had a pipe from the bottom where as the new tank has a fuel feed pipe exiting the top of the tank. I can understand that that the old fuel tank would not have this problem but surely there must be a way to stop this happening with the new set up, otherwise you would see boats being tossed about out of control all over the shop.

Does anybody know how to stop this happening again?

Suggest you check how far off the bottom is the pickup pipe just in case it was cut too short. How did you know the tank was 25% full? If by a gauge has it been calibrated? Some tanks have internal baffles to reduce fuel slosh although probably not needed on a 30 litre tank.

 

[PaulRainbow]

Pick up pipe comments are all very valid. Also, is it a proper fuel tank with baffles, if no baffles the fuel will be easily sloshed around.

 

[Littledan]

Hello and welcome to the forum.

A few questions:

• Did the fitter talk to you about fitting a new tank;
• Did you agree to the work being done;
• Why did the fitter decide to fit the tank in the location s/he did?

Can the new tank be moved to the position of the old tank?

I've never heard of waves causing fuel to 'swish about' and cause air locks as the bottom of the fuel line is close to the bottom of the tank.

Hi Sandy, Yes and Yes. The fitter said it would be a lot of trouble to remove the old tank, to access it he would have to cut the boot to bits.

 

[Littledan]

Apart from filling up when the fuel gets below about half, I don't know how to stop it happening, but a bulb pump in the system would simplify and speed up the bleeding process.

The fitter said to keep it filled. This is not practical though as there could be bad weather or swells. I will look into a bulb pump. Thanks Stemar

 

[Littledan]

Pick up pipe comments are all very valid. Also, is it a proper fuel tank with baffles, if no baffles the fuel will be easily sloshed around.

I'm sure it is a proper fuel tank, it looks legit. I was thinking the same thing about baffles. You would assume all marine tanks would have them.

 

[Freebee]

bulb pump is not a cure tho..... just a means to fast prime when it happens, need a detailed look at the pick up pipe and check for baffles also check level gauge is reading accurately could be it was more empty than 25%

the clue might be the fitter said to keep it filled-maybe he knows the pick up pipe is short????

 

[Littledan]

Suggest you check how far off the bottom is the pickup pipe just in case it was cut too short. How did you know the tank was 25% full? If by a gauge has it been calibrated? Some tanks have internal baffles to reduce fuel slosh although probably not needed on a 30 litre tank.

The fitter said he was going to check the pick up pipe. I visually checked the fuel and dipped a stick. I was checking for new marine fuel tanks online but none I found gave any information about baffles. Quite frankly I am baffled - I need to be able to rely on the engine, this is the reason I got a new one

 

[Littledan]

bulb pump is not a cure tho..... just a means to fast prime when it happens, need a detailed look at the pick up pipe and check for baffles also check level gauge is reading accurately could be it was more empty than 25%

the clue might be the fitter said to keep it filled-maybe he knows the pick up pipe is short????

Handy though.

 

[Freebee]

I think if possible you need to be with the fitter to understand what is going on.....you need to check not only that the pick up is going near but not close to the tank bottom but also the position in relation to the centreline of the boat for and aft..if its on one side and you heal the other way the fuel will move away from the pick up.

30 litres is not a lot of fuel, 25% is 7.5 litres, as you dipped the tank physically how deep is 25% full on the dipstick???

 

[Littledan]

I was thinking of ripping the new tank out and replacing a new tank with a long down pipe from the bottom. Maybe I can add another high tank with a down pipe to the one already installed. The extra range will be handy if the wind drops off. Can't seem to find any new fuel tanks that you can fit a hose from the bottom though.

 

[PCUK]

How about installing a small service tank with a bottom outlet, say five litres with an electric pump drawing from the main tank and auto cut-off for when full. This will ensure air can never enter the system.

 

[LittleSister]

I was thinking of ripping the new tank out and replacing a new tank with a long down pipe from the bottom. Maybe I can add another high tank with a down pipe to the one already installed. The extra range will be handy if the wind drops off. Can't seem to find any new fuel tanks that you can fit a hose from the bottom though.

Can you not fit a bottom outlet to your existing tank (or to a new tank if you replace the existing)?

I must say that I have never understood the advantage of a top-down 'pick up' outlet, and I'd be keen to hear an explanation.

My previous boat had a tank with a bottom outlet (actually just above the bottom in the side of the tank, and there was also a very useful drain plug in the bottom of the tank). That worked fine and seemed to me, in my ignorance, a great arrangement (a small sump, to collect any water/debris would have been ideal). A boatyard that did some other work commented on this, though, saying that it was not good practice because, they said, if you got a leak in a fuel pipe the whole of the content of the tank could drain into the boat. I couldn't see the logic to this, as the same would happen - by syphon - with a top outlet (unless the leak happened to be above the level of the top of the fuel, but that would apply equally with a bottom outlet).

 

[Littledan]

I think if possible you need to be with the fitter to understand what is going on.....you need to check not only that the pick up is going near but not close to the tank bottom but also the position in relation to the centreline of the boat for and aft..if its on one side and you heal the other way the fuel will move away from the pick up.

30 litres is not a lot of fuel, 25% is 7.5 litres, as you dipped the tank physically how deep is 25% full on the dipstick???

I don't see this making much difference when the boat is being tossed about. We were sometimes rocked starboard to port 60 degrees, If the tank is not baffled, the fuel is going to move very quickly with a good chance of any feed pipe sucking some air. How are baffles designed in a marine fuel tank are they squared, I would have to cut the tank open to see. I think the only way to be sure air can not access the feed pipe is to have a long down pipe from the bottom of the tank.

 

[Littledan]

Can you not fit a bottom outlet to your existing tank (or to a new tank if you replace the existing)?

I must say that I have never understood the advantage of a top-down 'pick up' outlet, and I'd be keen to hear an explanation.

My previous boat had a tank with a bottom outlet (actually just above the bottom in the side of the tank, and there was also a very useful drain plug in the bottom of the tank). That worked fine and seemed to me, in my ignorance, a great arrangement (a small sump, to collect any water/debris would have been ideal). A boatyard that did some other work commented on this, though, saying that it was not good practice because, they said, if you got a leak in a fuel pipe the whole of the content of the tank could drain into the boat. I couldn't see the logic to this, as the same would happen - by syphon - with a top outlet (unless the leak happened to be above the level of the top of the fuel, but that would apply equally with a bottom outlet).

My thoughts exactly - I think the new tank is sitting too close to the hull to fit a downpipe.

 

[LittleSister]

I think the only way to be sure air can not access the feed pipe is to have a long down pipe from the bottom of the tank.

`
Perhaps an alternative is a wider diameter (inch or so?) pipe (could be plastic or metal) around and concentric to the existing top-down pick-up pipe. Open at the bottom and with an air hole at the top it would, I think, maintain momentarily fuel around the pick-up pipe, even if the tank is briefly tilted or shaken such that air reaches the pick-up point.

 

[Littledan]

How about installing a small service tank with a bottom outlet, say five litres with an electric pump drawing from the main tank and auto cut-off for when full. This will ensure air can never enter the system.

Food for thought, cheers.

 

[jdc]

What shape is the tank? Perhaps the new one is shallower but wider than the original? (on my old Sadler the tank as fitted originally was a deep narrow one).

I also pretty much doubt 'having to take the boat apart' to remove a redundant tank. But having to take it apart to fit a new one in its place is more believable!