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Old 11-15-2012, 11:37 AM   #1
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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.
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Old 11-15-2012, 11:49 AM   #2
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Does it happen when the mains are running?

sd
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Old 11-15-2012, 01:53 PM   #3
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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.
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Old 11-15-2012, 05:39 PM   #4
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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.
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Old 11-15-2012, 09:49 PM   #5
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Quote:
Originally Posted by skipperdude
Does it happen when the mains are running?

sd
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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Old 11-16-2012, 09:38 AM   #6
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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?
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Old 11-16-2012, 10:46 AM   #7
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Quote:
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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.

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.
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Old 11-16-2012, 11:48 AM   #8
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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
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Old 11-17-2012, 07:23 AM   #9
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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.
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Old 11-18-2012, 04:43 PM   #10
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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
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Old 11-18-2012, 05:19 PM   #11
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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.
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Old 11-20-2012, 07:08 AM   #12
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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.
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Old 11-23-2012, 04:32 PM   #13
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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

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Old 11-23-2012, 05:01 PM   #14
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I would think it would only be an issue if the return over filled the daytank.

Some diesels return more than they burn.

Sd
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Old 11-23-2012, 05:14 PM   #15
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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?
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Old 11-23-2012, 06:34 PM   #16
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Like I said some diesels return more fuel than they burn.

sd
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Old 11-23-2012, 06:58 PM   #17
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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.
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Old 11-23-2012, 07:12 PM   #18
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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.

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Old 11-23-2012, 07:30 PM   #19
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Quote:
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Like I said some diesels return more fuel than they burn.

sd
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.
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Old 11-23-2012, 08:24 PM   #20
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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.
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