Fuel fill venting - Racor LG100

[6string]

I am refitting my boat with new fuel tanks. The single 110 gallon tank leaked and has been cut out. I am replacing it with three tanks as I can't get a 10' long tank in to the boat. I studied my vent line path yesterday and at the last 2 feet it goes up inside an area that would require cutting up the interior to get at the connection going to the fitting on the outside of the cabin trunk. I don't really want to cut that area up.

If I run the vent line from each of the three tanks into the one line going out, should I be putting a seperate Racor LG100 on each of the lines before the merge or can I put a single LG100 after the merge? I am not very familiar with how the LG100 works but understand that it is the best at preventing spills when the tank gets full. I'm not even sure if it is the right thing to do to put all three tanks into the one line going out. I can't imagine that it would be a problem as you can only fill one tank at a time.

Your thoughts are greatly appreciated as always.

Jeff
sv/ Fafaki-Tahi
Home Page

[GordMay]

Will you have a separate Fill, for each tank; or will you have a single Fill, and gravity manifold connecting the tanks?

Goto: http://www.a-filter.se/files/racor_products.pdf
Select “Section 2 - Marine”, then “Fuel/Air Separators”.

See also the excellent review at:
Foundation Findings #40 - Spill? What Spill?

[Pblais]

If you ran all three vents to one seperator then the back flow could go to the wrong tank and fail to trigger the shutoff at the pump and cause the fuel to spill on the deck. It might tend to enourage the flow to go to each tank in turn until all tanks were filled. Normally with one tank the resistance of the fuel flow will back up the filler and trip an auto shutoff quickly based on the size of the reservoir in the seprator (see review notes). The size of the racor adds to the ability to do this reliably. Since the seperator won't totally block the vent the fuel may not back up properly if one tank was less than full. If another tank did not have its fill open then it would tend to deter the flow into an unvented tank so it might still work. The configuration of the vent lines might be the telling factor.

If you used a fill manifold to have one deck fill for three tanks then you would want a similar manifold for the vent too. It also means when you switch from one tank to another you would switch the supply line, the return line, and the vent line. Having all the controls together could save the cost of two more seperators and two more deck fillers but may eat up savings in a manifold, fittings, and extra tubing. If you have to crawl around to get at them all then you may be making a setup that could cause you trouble if you forgot one manifold valve. 3 seperators means you can't screw it up.

You don't want any loops or low spots in the vent lines. It appears the seperator specs call for no less than 60 degrees from horizontal for the vent lines. You really do want fill and vent lines to be as short as possisble too and have as few fitting as possible. Fuel fittings are not cheap so the money side of this may be more conclusive.

I would think you could combine the outlet for multiple seperators assuming you don't fill more than one tank at a time. That could save the cost of three exterior ventsc but adds a manifold or two Y fittings. The flow on the seperator should handle a high speed deisel fill pump where the big trawlers fill 100's of gallons assuming a 5/8 inch vent line. Flow volume is not a problem with this unit and why the reviews seemed to like it the most.

For me I have two tanks one far forward and one all the way aft so combining lines is not practical at all.

[cal40john]

Originally Posted by Pblais

If you ran all three vents to one seperator then the back flow could go to the wrong tank and fail to trigger the shutoff at the pump and cause the fuel to spill on the deck. It might tend to enourage the flow to go to each tank in turn until all tanks were filled. Normally with one tank the resistance of the fuel flow will back up the filler and trip an auto shutoff quickly based on the size of the reservoir in the seprator (see review notes). The size of the racor adds to the ability to do this reliably. Since the seperator won't totally block the vent the fuel may not back up properly if one tank was less than full. If another tank did not have its fill open then it would tend to deter the flow into an unvented tank so it might still work. The configuration of the vent lines might be the telling factor.

If you used a fill manifold to have one deck fill for three tanks then you would want a similar manifold for the vent too. It also means when you switch from one tank to another you would switch the supply line, the return line, and the vent line. Having all the controls together could save the cost of two more seperators and two more deck fillers but may eat up savings in a manifold, fittings, and extra tubing. If you have to crawl around to get at them all then you may be making a setup that could cause you trouble if you forgot one manifold valve. 3 seperators means you can't screw it up.

You don't want any loops or low spots in the vent lines. It appears the seperator specs call for no less than 60 degrees from horizontal for the vent lines. You really do want fill and vent lines to be as short as possisble too and have as few fitting as possible. Fuel fittings are not cheap so the money side of this may be more conclusive.

I would think you could combine the outlet for multiple seperators assuming you don't fill more than one tank at a time. That could save the cost of three exterior ventsc but adds a manifold or two Y fittings. The flow on the seperator should handle a high speed deisel fill pump where the big trawlers fill 100's of gallons assuming a 5/8 inch vent line. Flow volume is not a problem with this unit and why the reviews seemed to like it the most.

For me I have two tanks one far forward and one all the way aft so combining lines is not practical at all.

Is it a good idea to seal off the vent lines to the other tanks not being used? Seems temperature and pressure fluctuations on a sealed tank might cause problems.

John

[Chief Engineer]

What is the schematic of your tanks/fill(s)?

Are you relying on this to automatically shut off the fuel?

How many gallons do you estimate that you put aboard each time you fuel?

[6string]

I have the system currently designed with 2 storage tanks of 55 gallons and a day tank of 28 gallons. There would be one fill on deck. It goes to a diverter valve. I would select between one of the two storage tanks. The day tank would be filled by a pump from the storage tanks with a filter in its line. This way only filtered fuel is in the operating tank . I am also planning on installing a filter boss into the system. I need to learn more about that system to know if it can be my means of transferring the fuel into the day tank.

Yes, I would like to have the fuel supply to automatically shut off. I don't want to deal with spillage.

I am currently in the final stages of designing the tanks and total system. I am looking for an effective system that is as simple as can be with what I am trying to do.

I do appreciate the help.

Jeff

[Chief Engineer]

My two cents FWIW.

On commercial vessels YOU NEVER rely on an automatic shutoff. This is because sometimes if the fuel delivery is too fast, by the time it shuts off you have a geyser of fuel coming out. You have to keep in mind that as you add fuel you are displacing air. Some diesel pumps can overwhelm the capacity of the venting system.

You also have to consider that the diverter valve is going to restrict the incoming fuel.

To keep it simple, if it was my boat, I would put two deck fills and two vents in.
Simpler plumbing.

[Pblais]

You have to keep in mind that as you add fuel you are displacing air. Some diesel pumps can overwhelm the capacity of the venting system.

The Racor should handle a high speed pump just fine but I doubt he would be using one.

Seems temperature and pressure fluctuations on a sealed tank might cause problems.

Yes, I would have to agree the vents need to be open except when filling fuel. The complexity seems over bearing and prone to operator screw up. We all have a bad day from time to time. Too much manual valve swapping just begs for a screwup.

The day tank would be filled by a pump from the storage tanks with a filter in its line. This way only filtered fuel is in the operating tank . I am also planning on installing a filter boss into the system.

I think you may be over complicating this. You still need a filter before the engine. A dual Racor filter system in front the the engine would handle the ability to change filters on the fly. It would be a self contained unit so no engineering required. Elimination of the day tank saves a lot of other hassle and now you no longer need the transfer pump. If you used an electric fuel pump you could then bleed the system in just a matter of minutes. It saves a $1,000 maybe more. It might be different if the tanks were 500 gallons each but 55 gallons is really not all that much fuel. The day tank just adds another tank to require cleaning. Fuel sitting the day tank is the same as fuel sitting in the main tank. The fact that it is half the size of your main tanks tells the story.

This is almost what I have now except my tanks are 30 and 38 gallons. I have a dual Racor that can switch over under power. I do have two deck fills and two vents due to tank locations. This system traveled 40,000 miles before I got the boat. The PO also had a Baja filter but said he never actually used it. A dual Racor 500 turbine filter will do the whole filter job just fine and has a built in backup. It's a luxury setup and would work better and cost less. DIY fuel systems just consume too much money and complicate operation. Get rid of as many feet of fuel line and fittings as possible. They can leak air.

[Chief Engineer]

Well Stated.

I have see to many boats that were overly complicated. Whether it is fuel, electrical or plumbing.

K.Y.S.S. Keep your systems simple.....Remember you might be in West Jesus some time and not be able to get a part....fitting.