Conundrum: Air in Racor Filters

[dheaslip]

I have two Norther Lights Lugger generators. Both have separate fuel pick ups from port & stb fuel tanks. Both have separate valves on the fuel manifold. Both have serarate racor fuel filters and priming pumps.

The problem is that suddenly both gennies have started losing power under load. When I lift the top of the racors both have a considerable amout of air in them. I fill the racors to the top, screw down the lid and fire up the gennie and we're back in business - for a while. Then the same problem starts up again.

When the problem first started I replaced the o-rings and filters in both racors, but it made no difference. The only common factor is the fuel. I recently filled the tanks in Tonga where the fuel seems to be of lower grade (we certainly get a lot more carbon deposits around the exhausts on the side of the hull). However I recall that the problem started before this latest fill-up.

I have checked the fuel lines (copper) from the tanks to the manifolds and can't see any leaks, although I agree that suction leaks would be hard to spot. I just can't figure out what's going on. The two systems are stand alone, so how can I have the same problem on both?

One further piece of information. I have the injectors serviced on both motors prior to leaving Mexico. Could this be a factor? Also, is the air the cause of hte engines struggling under load. This morning the gennie cut out, but there was only half and inch of air in the racor.

Thanks - I appreciate any assistance.

[DeepFrz]

Well, obviously you have an air leak prior to the Racor fuel filters. Start there and fix that and then see what happens. It sure seems to me from what you have said that filling the filters up clears up the problem until you get more air in the fuel filters, and I assume from there into the fuel injector pump.

[Tia Bu]

I had a somewhat similar problem earlier in the summer. It turned out I had two problems: 1) a couple of loose hose clamps on supply lines that let air into the system. and 2) a clogged tank pickup that slowed or stopped the fuel flow and caused the fuel pump to suck air into the system.

It took a meticulous (and no fun) day of going carefully over the whole fuel system to determine this and remedy it.

Good luck.

[DeepFrz]

What Tia Bu says makes sense. Certainly a good place to start. Run one Gen. from a clean container of fuel and see what happens. Disconnect the input line on the Racor and fit in a temporary line to a 5 gal. jug of filtered fuel.

[Chief Engineer]

Check the bowls for star cracks.

Jun each unit from a clean fuel supply thru racor. That will narrow down the aire leak on the vaccum side

[skipmac]

Originally Posted by DeepFrz

What Tia Bu says makes sense. Certainly a good place to start. Run one Gen. from a clean container of fuel and see what happens. Disconnect the input line on the Racor and fit in a temporary line to a 5 gal. jug of filtered fuel.

This would be my first step. It will allow you to isolate the problem to the Racor or the lines from the tank to the Racor. Once you have that, you're halfway done.

[skipmac]

Are both gennies completely separate from tank to engine or do they share a common fuel pickup or line at some point before the separate Racors?

[HopCar]

I kind of like what Tia Bu said. Pickups restricted, causes high vacuum, which reduces fuel flow to the engine and sucks air past the o-rings. It would be useful to have a vacuum gauge on the filter. You mentioned low grade fuel. It might have come with dirt big enough to clog the pick up screens. Bad fuel would affect both engines even if they draw from two separate tanks. Is it easy to pull a pickup tube?

[dheaslip]

Thank you all for your replies. Since the fuel systems for each gennie are completely separate the idea of blocked pick-ups seems likely. The chances of developing a leak in each system simultaneously seemed improbable. It also made me recall that I added biocide (for the first time) when I did my last fill up in Mexico. Could the biocide have caused extra deposits in the tanks that would block the pick-up filters?

[DeepFrz]

The biocides will kill any critters in the tank and they will precipitate out and land on the bottom. If there are lots they could block the pickup tubes, especially if the tubes have a screen on them. If they do, destroy them, throw them away or something but do not put screens on your pickup tubes ever.

Are your pickup lines for the gens. smaller diameter than for your main engine (s)? Just wondering because you don't mention any problem with the main.

Sounds like you could use a good fuel polishing system. I recommend you install it completely separate from the other fuel systems and with a pump that will circulate the tank through a filter at least once in an hour. Pickup and return tubes should go to near the bottom of the tank.

And, clean the tanks manually.

Those are my recommendations.

[HopCar]

I'm with DeepFrz on removing the screens. The first time one of mine clogged I yanked it out and threw it as far as I could. I want the dirt to go through to my filter where it is easy to get rid of it. When it happened to me I just had a problem with one tank. The engine ran fine on the other tank. I pulled the pickup tube expecting to see a clogged screen, there was no screen. I changed everything between the tank and the fuel manifold, engine still wouldn't run on that tank. I pulled the pick up tube again and looked more closely at it. I saw that the tube would unscrew from the fitting at the top. Sure enough the screen was at the top of the tube and well plugged with some black granular stuff. I threw away the screen and haven't had a problem since.

[DeepFrz]

Although I just posted this link about a week ago I am posting it again because it may have bearing on this specific problem. Maybe not but it doesn't hurt. It is an interesting short read that explains some of the problems being experienced with diesel fuel these days. I thought the problem was getting worse and this article confirms that. I can't vouch for its scientific correctness however the writer does have impressive credentials in this field.

Fuel School: Asphaltene's and Plugged Fuel Filters

I believe that the article shows that a good, well engineered fuel polishing system is becoming even more valuable than it used to be with the LSD fuel (easy now, no hallucinating. ).

Edit: add following
There is also a more indepth article on diesel in a newer entry.

http://fuelschool.blogspot.com/2011/...uels-2011.html