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Old 12-04-2021, 04:05 PM   #1
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fuel filtering/polishing flow rate question

Good afternoon. New member... sorting out the mechanics of the forums. I am installing a homemade polisher. seperate loop from engine. I have a walbro 40gph pump and filter rated for same but the math of fuel supply line/flow rate is beyond me. I'm thinkin' 1/2 ID will get the job done but I prefer 3/8. Anyone have an opinion (or any rocket scientists that can manage the calculations) on whether or not 3/8" is big 'nuf? Thanks.
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Old 12-04-2021, 04:24 PM   #2
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I run 1/2" on mine and it's 2 GPM. You will be absolutely fine with 3/8". Don't go smaller as the risk of something plugging the hose will dramatically increase.

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Old 12-04-2021, 05:18 PM   #3
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How long are the hose runs? The flow resistance per foot is based on the hose size. Then you multiply it by the hose length. From that you can figure out the back pressure, and from the pump specs, you can see how much flow reduction you will get. But that's probably more worry than necessary.


Personally I'd go with 1/2" just because it's easy and cheap to do it now. But if the hose lengths are short, 3/8" is probably fine.
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Old 12-04-2021, 07:06 PM   #4
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Welcome aboard. I think you will be ok with 3/8Ē hose.
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Old 12-04-2021, 11:45 PM   #5
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Focus on getting good filtration, + or - hose size just means a little slower or faster work.
If you don’t have great filtration with large capacity to handle crazy shit like a load of water laden fuel, you’re wasting your time.
I had a polishing system and removed it in favor of more stages/capacity of filtration in the main fuel supply system.
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Old 12-04-2021, 11:52 PM   #6
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PassageMaker Magazine, back when it was good, really promoted fuel polishing systems, but really I have never had any issues with dirty fuel that the primary filters couldnít deal with. As long as you are not fueling from a fuel dock that doesnít pump much fuel at all, you should be fine without a polishing system.
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Old 12-05-2021, 04:11 AM   #7
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Quote:
Originally Posted by kapnd View Post
Focus on getting good filtration, + or - hose size just means a little slower or faster work.
If you donít have great filtration with large capacity to handle crazy shit like a load of water laden fuel, youíre wasting your time.
I had a polishing system and removed it in favor of more stages/capacity of filtration in the main fuel supply system.
+1. As Comodave says, good sequential filtration is all you need. That, and vacuum gauges. IMHO, fuel polishing and the use of day tanks are a waste of time and money. But, mine is just one opinion. I would be happy to acquire a boat that already has a system in place, at someone else's expense, then remove it and sell it all to to fund other needs.
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Old 12-05-2021, 08:20 AM   #8
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Obviously I'm a proponent of having a polishing system as I have one. It also serves to move fuel between my tanks. I have had 2 batches of bad fuel in 6 years. Neither was catastrophic, and both were removed by the polisher before they reached the main filters. Imo, if you cruise and buy fuel at different places, getting some bad fuel is a very real possibility. Having a clear bowl on the bottom of your polishing filter (such as a Racor) can alert you to a potential problem before it shuts you down. I run my polisher and transfer fuel about every 3rd cruising day before moving the boat while I do fluid level checks. The draws are at the lowest point of each tank. A minute of polishing tells me if there's anything in the very bottom of tank.

The other nice feature of a fuel polisher is the ability to deal with a large quantity of contamination. Visualize getting 5 gallons of bad fuel in a 300 gallon load. Much of the contamination would separate and collect in the transparent bowl of my Racor 1000 polishing filter. So I can watch the bowl fill with contaminants, shut the pump off, drain the bowl into another container, and repeat.

Some engines (such as a Lehman) return almost no fuel. So contamination can collect for years in the bottom of a fuel tank until the fateful day when you're out in heavy seas and all that stuff at the bottom gets stirring up and shuts down your engine. A friend of mine with a 42 Krogen with a Lehman now has a Racor 900 with a piston style 30 GPH electric fuel pump. He runs it while cruising to supplement the miniscule frow of the Lehman.

It's also important to understand that fuel contamination isn't only from buying bad fuel. Boats that sit (sometimes for years) precipitate asphaltene out of the fuel. A significant quantity of this collecting at the bottom of the fuel tank, can easily plug a primary filter when stirred up. Water can also enter the tank from a bad oring on a deck fill port.

Lots of good reasons to have a polishing system. A large Racor separator filter and a piston style electric fuel pump can be had for under $500.

Ted
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Old 12-05-2021, 01:44 PM   #9
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fuel filtering/polishing flow rate question answered

Thanks for replies. I am a finished product as regards the pro-s and con-s. I accept the arguments against polishing as credible; I just don't happen to agree with them for my particular application. I bleev 1/2" hoses connected to pickup/return tubes at opposite ends of the tank and a bit of aggitation with compressed air will give me some flow across the bottom of the tank. With a 40 gph pump and depth type filter element I think that is as close to a true polisher as a lnon-engineer can get. I borescoped my tanks and saw sparse to moderate blooming on bottom... don't want moderate to progress to severe. Bought 3/8 line for polisher cuz the pipe fittings are all 3/8. Duh. The pipe fittings are 3/8 npt but the ID is 1/2"... guess we'll head back to western hose and gasket. Pleasant Sunday to all.
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Old 12-05-2021, 01:52 PM   #10
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Certainly a good choice to utilize 1/2" with 3/8" pipe fittings. Running the fuel polisher with 1/3 tankage in beam seas does a good job mixing up and filtering tank contents.

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Old 12-05-2021, 04:13 PM   #11
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Some engines push enough fuel around not to need an extra fuel polishing system
Eg: our 855 Cummins pushes around 250 litres/hour through the filters, uses 15 of them

Check specs on your's
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Old 12-05-2021, 06:53 PM   #12
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single CAT 3116. I know it returns a lot more than it burns... I guess I could look up the numbers, but the polisher seems like a good sleeping pill to me. I have to mange 300 gallons and I don't get underway that much.
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Old 12-05-2021, 09:41 PM   #13
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I have a fuel polishing system and mostly use it for transfer of fuel between the 4 tanks.

ButÖ

Öfor a fuel polishing system to be of any use, you MUST HAVE agitation in the tanks. I.E. you need to be in rough seas and ideally you need to have the tank being filtered to be 1/4 full or less.

Öthe fuel has to slosh around to lift the crud at the bottom the tank into suspension. So if itís an AC powered pump it needs to be on the inverter.

Jim
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Old 12-06-2021, 12:12 AM   #14
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Using a good fuel conditioner/stabilizer makes a huge difference. Best ones have a biocide, increase combustion efficiency, slowly dissolving sludge, add lubricating qualities, help filters separate water, corrosion inhibitor, besides stabilizing the fuel for a year or more.
If you have an engine that returns a small amount of fuel to the tank, a pump for polishing will help. It needs to draw thru a primary filter like a Racor that separates out water. Preferably a turbine. If your primary filter is rated for the engine's flow plus the pump flow rating, then you can run them both at the same time.
Using a conditioner with a polishing system or an engine that returns a high amount of fuel to the tank, your tank will slowly be cleaned of sludge and water. The sludge won't quickly clog your filter, but dissolve over weeks or months. In the end, with care, your tanks will be clean.

The conditioner I use (Archoil 6200) costs about 9Ę/gallon. It gives me 6% better mileage besides all the other benefits. I cruise at 10 knots and burn about 9 gallons, or about 8.4 gallons using Archoil. So every hour I save about $1.50 worth of diesel for about 35Ę. Conditioners pay. And there's a newer type (AR6500) that's advertised to increase mileage 11% I haven't tried yet. My tanks are clean, and I can go inside, walk around, and verify that. I run 2 micron primary filters, have really clean fuel and haven't changed an injector, fuel pump, or fuel system part in 10 years.
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Old 12-06-2021, 05:15 AM   #15
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Just make sure you use a large enough water separating filter in your polishing system.
A Racor 1000 would be a good start, and it has high flow rates, and water drains.
You may want to increase your pump size.
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Old 12-06-2021, 06:56 AM   #16
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It is a delight that some styles of engine fuel systems will slowly clean the fuel system.

The best filter monitor setup for these is with a DP (differential pressure) gauge.

This measures the difference across the filter , so as it slowly gets plugged , you can decide when the filter should be changed.
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Old 12-06-2021, 04:14 PM   #17
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Rough seas? What does that mean? San Diego is my theater of operations. We don't understand that phrase here. My ex wife is a pretty respectable agitator... Kidding aside Ill be agitating with compressed air.
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Old 12-06-2021, 04:34 PM   #18
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I use biobor and stanadyne cuz that's what my CAT guy recommended. I suspect my CAT 3116 returns a lot more fuel to the tanks than it burns... I have primary 30 mic racor 900 and CAT spin on secondary. My polisher is a separate loop. Separate tank pickups, pump and motor and element. I can polish as I run the engine but do not intend to. Also intend to use polisher for fuel transfer and to fill up my little Ranger Tug.

My life experience is that magic in a bottle never works. Stop leak will sometimes stop a leak and who knows for a fact whether injector cleaner actually does you any good? Ill use these products for maintenance purposes but I am skeptical about matter-of-fact claims such as "6% increase in mileage". How would you even know? Too many variables to accurately measure mileage. Your savings would probably he within the range of error if it were calculated under "lab conditions".

The proof will be in the pudding as regards tank cleanliness. Borescope is a pretty cheap tool to look inside the tanks and remove all doubt.
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Old 12-06-2021, 04:36 PM   #19
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Racor 900 30 mic primary. Gulf Coast F-1 on the polisher. Polishing and running the engine are independent of each other in my application.
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Old 12-06-2021, 04:43 PM   #20
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I have vacuum gauge on primary and on polisher. Recently I started the engine with tank supply valve closed by accident. Primary vacuum gauge shot up like a rocket prompting manual shutdown before fuel starvation. Good operational test even tho unintentional. Thanks for bringing forward the issue of defacto polishing just by running the engine due to large amount of fuel return that has been run through the filters. Never thought of that... Brilliant concept in it's simplicity.
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