How far can an engine suck?

[Billyo]

So in the replacement of my engine I've taken the opportunity to strip out and replace the existing fuel system.

Id like to put the Raccors for both the engine and the genny on the aft wall of the engine room so that they are easy access for changing and cleaning. This would make a 6.5 metre draw from the bottom of the tank to the engine and generator. I've looked at the manufacturers websites and can find no reference to a max distance, so can I assume that this will be OK? Or should I work with the existing locations?

Many thanks

* I should (as it might help) add that the new engine is a Beta 50 and and genny is a 4.5 kw Northern lights.

 

[pvb]

Height of fuel draw is generally more important than distance.

 

[Topcat47]

Height of fuel draw is generally more important than distance.

Yes this is true. As long as you can fill the line, something gravity can do for you if the tank is above the level of the lift Pump. Most modern tanks have fuel taken from a fitting at the top of the tank and in many installations, getting rid of the air lock at the top of the loop is a problem. To overcome this, many people fit a squeeze bulb from an outboard fuel line in the inboard system, just to get fuel from the take of point to the filters. Once you have fuel in the line to the lift pump, all will be well. Any air in the line will interfere with the flow. In my installation, the primary filters are lower than the lift pump. Although there is a flexible fuel line from the filter to the lift pump, I have little trouble bleeding the system.

 

[macd]

Billyo: our boat had a tank a similar distance from the engine when we bought her. There were no fuelling issues at all, despite the head of fuel being quite modest.

 

[jwilson]

snipped -- many people fit a squeeze bulb from an outboard fuel line in the inboard system, just to get fuel from the take of point to the filters.

Many people do, and it certainly can help bleeding, but it looks to me like a very weak point in the system from a fire extinguishing perspective.

 

[JumbleDuck]

I've just been doing some calculations on the pressure needed to force 2 gallons of petrol per hour through a 6mm OD pipe, trying to solve a fuel starvation on my car. Flow was just turbulent and the pressure drop was about 0.03bar. It'll be lot more for diesel, being more viscous, but as others have said I would expect the static pressure from the 6.5m height difference to be far, far more of an issue.

 

[pvb]

.... I would expect the static pressure from the 6.5m height difference to be far, far more of an issue.

I think the OP's 6.5m measurement was the length of the fuel pipe, not the height difference.

 

[Keith-i]

Presumably, if you have any real concern you could just use a larger diameter feed pipe.

 

[Deleted member 36384]

If it's a seagull, they suck a lot.



I'll get my coat.

 

[JumbleDuck]

I think the OP's 6.5m measurement was the length of the fuel pipe, not the height difference.

Oops. Good point. But even a small difference will probably matter ... I'm currently trying to persuade a brand new genuine Facet to get fuel over a 1 foot "hump" coming out of the tank.

 

[macd]

I'm currently trying to persuade a brand new genuine Facet to get fuel over a 1 foot "hump" coming out of the tank.

Are you sure the pump's in the correct place, JD? Some Facet pumps must be installed close to the tank and low down (they 'push' much better than they 'pull', to quote their literature). Some don't, but worth checking the small print.

 

[Billyo]

Thanks for the replies, for clarity, I did mean that the total run length from the tank to the engine is 6.5m.

The route is a little convoluted, and the total lift over the whole length will be 1.4 m so thinking I will need to instal a lift pump. I will look at the facets as they are popular over here.

 

[rotrax]

I had a Ducato single cylinder diesel in a canalboat once.

That REALLY sucked...............................................

 

[RichardS]

This engine can suck a couple of metres ..... unfortunately. :ambivalence:

Richard

 

[DownWest]

Blimey, this is drifting a bit..
I fitted a 'facit' like pump to my Renault, to try and cure a problem with the injector pump. Didn't help, but pulled quickly from the tank with air in the pipe.

 

[JumbleDuck]

Are you sure the pump's in the correct place, JD? Some Facet pumps must be installed close to the tank and low down (they 'push' much better than they 'pull', to quote their literature). Some don't, but worth checking the small print.

Myes, that's what I'm wondering. Stuff-all suction at the tank, but stuff-all suction at the pump inlet too. I can prime it as I prime the original mechanical pump, by blowing into the petrol filler, but even with the fuel line full the Facet stops pumping after two strokes.

Too hot to work on cars now. I'm going sailing and will investigate in detail one traditional Scottish summer weather has returned.

 

[macd]

if it' anything like ours, JD, the note changes markedly when it pumps fuel rather than air. It's quite noisy and 'busy' when priming, then settles down to a contented hum. It's installed level with the bottom of the tank, and about 300mm away, the supply coming direct from low on the tank face with no loop.

 

[bluerm166]

The Beta installation guide states that all engines will lift only to 0.25M confirming the need for a lift pump.

 

[macd]

The route is a little convoluted, and the total lift over the whole length will be 1.4 m so thinking I will need to instal a lift pump. I will look at the facets as they are popular over here.

The 1.4m is rather more critical than the 6.5m you mentioned earlier.

They're popular where you are for two reasons.
1. They have a reputation for reliability.
2. They're a US company (albeit several thousand miles from you).
Beta includes a Facet pump amongst its list of options, although you'll surely be able to source one cheaper where you live. I'd be inclined to ask Beta which particular Facet pump they recommend. We have one, also on a Beta 50 and it's been utterly trouble-free, but do heed my comments in post #11 about its installation. (I'd be happy to check its model number, but the boat's currently several hundred miles away.)

The Beta installation guide states that all engines will lift only to 0.25M confirming the need for a lift pump.

I'm pretty sure Beta used to quote 0.5m, but are perhaps being more conservative in the light of experience. Regardless, a 1.4m lift is way too much.

 

[Billyo]

Spoke to Beta and the maximum reccomended lift it 25cm, so a facet pump is the way forward.

Thanks for all the guidance!