Inadequate fuel supply to generators

I am having a problem presumably with fuel supply to my generators. We have two, a 15 and a 40. Don't use the 40 very often but we have 120,000 BTUs of AC and cook with electriicity , and have some big compressors, etc., so sometimes in the summertime we need it. Both gensets are relatively new, both with less than 1000 hours. The fuel supply comes from a supply manifold using the same valve as the engines. From there it runs to a dedicated genertor Racor and then aft where the two gens are located. There is a 20 foot run of 3/8's copper from the Racor to where the 15 "t's" off and from there it runs to the 40, about another 15 feet.
The problem is that I have great difficulty getting them to start even with a boost pump at the manifold running. Cold weather, warm weather... no difference. Doesnt seem to make any difference if the gens have been used a lot recently or not. Once they start they will run all day long and never miss a lick. But when I turn then off, sometimes they won't start again even is still warm. On the other hand sometimes when they have been sitting for a few days unused they fire right up. Both are Westerbekes and have fuel pumps that are energized by the preheat switch. I have changed all of the filters, racor and primary and seconday filters on the gensets. I do not have a problem with either of the Cummins propulsion engines. They fire right up and share the same supply but have their own Racors. .
Someone has suggested that one generator is sucking the fuel out of the other and that using some check valves might help but I have not tried this as someone else said that the fuel pumps dont generate enough negative pressure to flow through a check and it would restrict fuel flow. Another person suggested that the long run from the manifold to the generators was the problem but even with the boost pump running it continues to be a problem. Any one have any brilliant ideas?

I cannot remember if this is a new problem but it did not seem to be a problem when we launched the boat so I suspect its a new problem. Any help would be welcomed.

Does it happen when the mains are running?

sd

It sound like something is sucking the fuel from the gen sets, either the main and or the other gen set. Might want to add some values to close off when not in use rather than one ways.

Why are there two separate filters, if the fuel is from the same source and manifold. One set of filers would be needed and one booster pump if they were before the manifold. Then the booster pump would prime all the fuel lines. The way I set up the Eagle is the 1000 double Racors, and fuel pump is before the manifold that has valves you can open close.

When we installed the Webasto the 671 would suck/starve the Wegasto. So had to close down the return valve for the 671 so the return capacity is not more than the draw. The 671 can draw/return about 60 gph. I set the return valve by the feel of pumps, so the pump was not running full/wide open, so the 671 can not starve the gen set and/or the Webasto. When not running the valves are closed.

Doc, couple of thoughts:

Do you run the boost pump whenever you run the generator(s)? The pump might restrict/prevent flow when it's not running.

With the booster pump running, check for good fuel supply at each generator. If good flow, start an engine or two and check again. This might give you a clue.

Please post what the problem was when you find it.

Good luck.

skipperdude said:

Does it happen when the mains are running?

sd

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Yes it will but we generally start the generator before we fire the mains. The generator panels are located in the salon over one of the mains. The generators are well insulated for sound so it's hard to hear what's going on if the mains are running. You can't hear the generators cranking or trying to fire with the engines running.

That's a beautiful ship Whistledoc!

Do the engines have external injectors/ lines? Can you crack one or two and watch for lack of fuel when first spinning over? Is there a mechanical priming pump on the transfer fuel pump on the engines? If so, can you crack a line/ banjo fitting somewhere past the transfer pump and then operate the lever to look for an indication of air?

Whistledoc said:

Yes it will but we generally start the generator before we fire the mains. The generator panels are located in the salon over one of the mains. The generators are well insulated for sound so it's hard to hear what's going on if the mains are running. You can't hear the generators cranking or trying to fire with the engines running.

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I installed starts button for the main and gen set in the engine room. I initailly start the engines fron the engine room as I have to open the raw water valves, turn on the batteries, make sure the fuel valves are open/close correctly and turn on the fuel pump to to make sure the fuel lines are primed. The engines start in less than 5 seconds. If more I stop cranking as something is wrong. I try to shut the mian engine down first as it can draw/suck all the fuel.

Also you could install a small clear in line fuel filter. I did that to find small air leaks and/or to see if there is an air leak.

I guess I should have said. Does it happen reguardless of if the mains are running or not.

If you are sure you are getting fuel.

One thought is to check the wiring for the preheat. There could be a voltage drop or the connection doesn't always work.

Not allowing the preheater to work properly.

If the preheat on the glow plugs arn't getting the juice they may not allow it to start.

Sd

Most setups like yours will have a check valve in the system for each gen set that should stop the fuel from draining back. I would clean them.

Second cause could be a small air leak, which helps the fuel drain back..

Your aux fuel pump is probably pushing against a line full of air , so it still takes a long time to fire.

Best way to look for air leaks is to pressurize the lines , and wrap each fitting overnight with a strip of paper towel.

Good Hunting.

Plan B would be a buypass setup for priming.

I want to thank you all for your responses to my problem. Everyone has valid suggestions. I think one of the major issues is the distance from the fuel supply manifold to the actual generator. For the 40kw it is something like 35 feet and for the 15 it's somewhat less maybe 25 feet. From the supply manifold to the point that the two generator lines "t" is about 20 feet. Both of the generators have. 12 volt priming fuel pumps tied into the preheat system. I suspect that part of the issue is that the pumps may not generate enough negative pressure when running to lift fuel from the bottom of the fuel tank and pull it 25-35 feet. My plan is to put an accumulator tank or day tank at the point where they "t". If that doesn't help I will add a check valve between the accumulator and the supply. My reluctance to add the check valve initially is that it just adds more resistance to flow in what may be an already compromised situation.
I think it's unlikely that I have air leaks on both generators as I have gone through them several times. I have checked both generators for fuel leaks and found none. I did the by cutting up small pieces of oil absorbant pads (we call them diapers) and tie-wrapping them to every conection in the entire system and running both gens with the boost pump on. If there is any leak at all the pad material will be a tell tale pink from the dye in the diesel. Is it possible to have an air leak at a connection that would let the fuel siphon back downhill but not leak fuel under pressure?

Ron

I had almost the same problem where I had my genset and main engine "T" off a single filter. After running the main for any length of time, the genset fuel line (about 8') would get air sucked back thru it and not allow the genset to start (or die after a minute or two). A simple dedicated feed from the fuel system intake manifold to a dedicated small spin-on filter fixed the issue.

From the supply manifold to the point that the two generator lines "t" is about 20 feet.

Agree , with Gonzo,

The best solution is a single line for each user from its own tank pickup.

The T "solution" is normally a disaster.

I am planning on putting day tank or what I call accumulator tank on both generators. Planning on using one of the 11 gallon steel tire fill tanks that I can buy at an auto supply store. The day tank will feed off the main fuel manifold. The pick up for the generator will be in the bottom of the day tank. Question is: Can I run the returm line from the generator to the day tank or does it need to go all the way back to the return manifold at the main tanks. I don't see why I couldnt just dump the return line into the top of the day tank unless I am missing something.
Thanks

Ron

I would think it would only be an issue if the return over filled the daytank.

Some diesels return more than they burn.

Sd

Not sure how it could overflow the tank, unless the engine produced fuel instead of consumed it?

The only issue I have ever heard of, with a pump continuously circulating the fuel, would be a temperature rise of the fuel, especially if the day tank is too small.

Wouldn't the day tank have an overflow as well?

Like I said some diesels return more fuel than they burn.

sd

If you want to return it to the day tank, it would be ok, but do a test to see how much it returns. Just run it for an hour and dump it into a gallon jug or something. Although, if you just fill the day tank once a day, unless you have a continuous flow from the regular tanks, you won't have a problem. My genset burns and returns nearly nothing. Pints per hour.

The amount of any fuel returning to the tank will be less than is sent to the engine because the engine will be consuming fuel. On the other hand, if the fuel is returned to a different tank than from which it is being taken, that tank could overflow. I routinely check the tank valves thrice when switching tanks as it is common for me to make mistakes.

skipperdude said:

Like I said some diesels return more fuel than they burn.

sd

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100% leaves day tank through pump and filter
20% consumed by engine
80% returned to day tank

Yes, more returned to tank than cosumed by engine, but not more than originally left the tank.

Our two FL120s normally feed from the 60 gallon day tank. The fuel returns from both engines are normally valved to the day tank. No problems with overfilling the day tank at all. Of course FL120s return very little fuel. Some other engines return a lot more.

There are bronze marine fuel valves that switch both the supply and return at the same time.

A far better easy to use solution than a fuel manifold with gaggle ball valves.

Zero understanding is required when switching from Tank 1 to Tank 2 ,

Of course it doesn't matter how much fuel an engine returns--- if you send the fuel return to the same tank the engine is pulling from it will never overfill unless you have an engine that actually makes fuel, in which case you will have solved the world's energy problems and will become a bazillionaire and can afford a boat with any range you want.

FF said:

There are bronze marine fuel valves that switch both the supply and return at the same time.

A far better easy to use solution than a fuel manifold with gaggle ball valves.

Zero understanding is required when switching from Tank 1 to Tank 2 ,

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The Coot has four fuel tanks and two fuel manifolds. One manifold selects the source of fuel for the engine and the other manifold selects which tank fuel is returned from the engine. I look forward to the puzzle of selecting the correct combination of valves.

I look forward to the puzzle of selecting the correct combination of valves.

Always the most fun when a bit of mal de mere strikes , and the engine stops while climbing 5- 15 ft waves every 6 seconds.

Talk about FUN TIME!

theran5317 said:

100% leaves day tank through pump and filter
20% consumed by engine
80% returned to day tank

Yes, more returned to tank than consumed by engine, but not more than originally left the tank.

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Sorry I mis read the statement.
I wasn't sure how the day tank was filled to start with. I was thinking the return was off the main.
Op says off the manifold. If he wasn't sure how much fuel was in the tank to start with or the manifold was open to the day tank. Then the return could over fill the day tank.

If there was an overfill line that would dump fuel back into the main tank
coming off the day tank.

Thinking about it. How will the OP know how much fuel is in the day tank?
He didn't indicate this. Is there a Gage.

Sd

SD

FF says "a gaggle of ball valves" ---------

My "gaggle of ball valves" (15 or so) is nicely laid out, well labeled and stacked on a nice SS header. DeFever has done this decently for many years. The setup involves:

• 4 tanks,
• 3 engines,
• ability to return engines' o'flow to any tank,
• a line to pump diesel to a temporary deck tank if one needed
• and fuel transfer between any of the tanks via a dedicated pump.

Nordhavns and other high end yachts have a "gaggle of ball valves" - in my contacts with Nordhavn blue water cruisers I've not heard that their "gaggle of Ball valves" has created issues. I'd love to post a picture, but we don't live close to the boat.

Ball valves don't travel in gaggles. A lot of ball valves in a group is called a herd.

skipperdude said:

w how much fuel is in the day tank?
He didn't indicate this. Is there a Gage.

SD

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In our case the four saddle tanks that feed the 60 gallon day tank via gravity from their lowest point through manual valves have sight gauges. The day tank, which is in the bilge umder the floor plates between the engines, also feeds from its lowest point but it has an electric level sensor connected to a fuel gauge on the instrument panel.

GonzoF1 said:

Ball valves don't travel in gaggles. A lot of ball valves in a group is called a herd.

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Sure I've herd of ball valves.

SD

Ball valves don't travel in gaggles.

A low buck trick , loved by the Maineiac lobster folks is a short coupling between ball valves.

Ganged valves can make multiple selections with no thinklng , just like the real marine fuel valves, at a lower price.