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Building a fuel polishing system - problem


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What happens when the diesel pump you got cheap flows twice the amount of fuel (theoretically) than the diesel filter you got cheap?

 

I have a 110L tank, so I bought a 110L/hr pump...turns out the filter (filter/separator) only flows 45L/hr.

 

Is the filter going to implode? Is the pump going to explode?

 

John

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What is the pump?

I assume you are using a CAV filter. That's the one with the glass bowl on the bottom. Can't think of anything much cheaper than those and still have it work well enough to be worth the effort.

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It is a cav filter (5-7 micron). The pump is a Facet style cube pump, very similar to the lift pump on the boat's engine. 5/9 psi, 110l/hr is what they claim.

 

 

 

 

 

What is the pump?

I assume you are using a CAV filter. That's the one with the glass bowl on the bottom. Can't think of anything much cheaper than those and still have it work well enough to be worth the effort.

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I have a full fuel polishing system.

It has two CAV filters. twin tanks and a day tank.

The pump is a higher rating than yours.

(edit) it runs at 60 psi ...and does more like 600 litres an hour....plus.

It works just fine. (close to a thousand hours and counting)

I have built a timer so that the pump fills the day tank from either of the main tanks and overflows back to either of the main tanks. (1.5 minutes , 4 times an hour). It has an override for dumping one tank to the other.

The CAV stats are usually just maximum possible fuel flow.

If its a reasonable fuel pump it is only seeing back pressure , (just like pumping up a distance) and wont be effected either. Its just that the actual fuel flow will be throttled back by the filter.

As an aside the CAV glass bowls do not pass some forms of commercial survey.

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As a further thought, try and set your system up so that if the polishing system fails you can plumb directly from the/a main tank to the engine via an inline filter.

This is as simple as having a length of hose and two hose clamps. (and pipe size adapters if needed).

A good size day tank is very worthwhile. I can get 2 hours run time from mine.

It means that I can swop out filters on the run, get into an anchorage, or prepare a bypass hose with the engine still going.

My system has six valves and the filters mounted on a board with flow directions and other labels.

Makes it easier when I am doing the very late at night change over from one tank to another.

 

Yes to those smarty pants...it is a sailing boat, but I often chose to motor in a calm than sail in a storm :D

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The CAV filters are ideal. Great Filter for the price and beats many other more expensive units, with replacement cartridges being cheap and readily available. The pump/filter combo will be fine. The pumps are not high pressure and will happily operate against a complete blockage, so will actually just slow down volume to meet the flow of the filter. The only real issue if you can call it that, is whether the combo has enough total flow to cycle your tank/s enough to warrant worrying about having the system.

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Thanks for the replies.

 

My polishing system is independent of the engine fueling system, I can run the boat on the day tank while I polish the main tank. The day tank holds 20l, which is almost 10hrs cruising (Westerbeke 35D3).

 

The engine supply has 3 filters, one of which is a Racor filter/sep with a 5 micron element.

 

I filled my main tank up last year and recently pumped it all out and burned it in my ute, I just don't use very much fuel. Im building this system so that if I ever fill the main up again (the mythical cruise next summer), I won't have to stress about the diesel going nasty (I keep it topped up).

 

It's also a lot of cool brass valves...I like 'systems'

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It's all about circulating and making the Fuel move, so as to ensure that once in a while all the Fuel has traveled through the polishing filter to ensure it is clean and water doesn't settle to the bottom of the tank.

Removing the fuel is one way of keeping it fresh, or you can add a bottle of a Diesel Fuel Stabilizer/biocide to prevent any bug growth.

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Do you have a sludge / water fitting at the lowest point of you main tank?

 

Makes draining any water off much easier.

Though if you are running your system 24/7 it would be pointless.

But if not you could tap off a bit and see if you have any water or bug very easily.

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Riggers 100% on. With no water, you have no other problems. And the one issue with Fuel Polishing is that it adds that little extra complexity and we can all do without complexity on Sailing Vessels. Having a drain point and even better, a shape in the tank so as anything heads to that point and is trapped there till drained, is probably the best idea ever in a Fuel tank and yet harder to find than an Aircraft in the Indian Ocean.

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Question - I have now sailed somewhere between 100 and 200k miles and I have never had such a thing and have never had a problem, and a lot of those miles were in funky 3rd world countries. the most high tech I ever got was a thing called a Baja filter which was a funnel with a screen used when filling tanks. And as of today I have never had an issue.

 

So am I just lucky?

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Thankfully it is rare. But it can happen and I have come across it 3 times over my lifetime. One was on a boat with very old tanks, not a lot of use, poor maintenance. Another was contaminated fuel from the Dock supply. Still a very rare issue in NZ. And the third was my own experience after putting 200+ ltrs into my Fuel tank when we first got the boat, due to previous owner having a Blue Water cap fitted to the filler of the Fuel tank.

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Question - I have now sailed somewhere between 100 and 200k miles and I have never had such a thing and have never had a problem, and a lot of those miles were in funky 3rd world countries. the most high tech I ever got was a thing called a Baja filter which was a funnel with a screen used when filling tanks. And as of today I have never had an issue.

 

So am I just lucky?

 

I've only had experience of this on ships, where cleaning up fuel, running out of filters and rebuilding centrifuges is a way of life if you're running dieso. The primary issue is keeping water out of your fuel, to avoid Micro Biological Growth (MBG) which is going to clog up your on engine filters and fuel systems. Obviously water in fuel is a bad thing just in itself.

 

This is only really a problem if your bunkering fuel for long periods, you can't trust your fuel sources or you don't have clean tanks or all of the above. On yachts, you probably aren't bunkering much if any fuel at all and you're probably turning it over often. Probably the fuel you are taking on is also stored in relatively small quantities and turned over fast and because of that turnover, probably in clean tanks. So its probably not luck, its just that the type of vessel and how you've been operating doesn't need a polishing system.

 

Maybe the only luck you have had is not taking on fuel that already has MBG contamination. Even with a polishing system you are buggered then, usually a pump out and clean of your tanks is required.

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Also makes a difference if you don't have metal fuel tanks - less condensation, therefore less water. I have GRP tanks, and I'd never had an issue until we got crappy, water contaminated fuel in SE Asia.

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My polishing system is just an extension of the fuel transfer system.

Having twin main tanks both in the keel, its better to pump up into a day tank. The filters are there as primary filters anyway.By adding a cross over line and two extra valves I have a full tank to tank polishing system.

...and the benefits mentioned in earlier posts.

My pick up straws are 20mm above tank bottom, with the return only a few mm off.

This stirs the bottom, helping to pull out water and suspended solids constantly. A better thing than allowing a build up.

If the tanks a left for awhile I can remove the hose to the return line and draw off and discard.

For a full tank clean a smaller straw is inserted through the welded one and again draw off and discard.

(A useful trick on any fixed tank)

Removable plastic insert tanks moulded to shape would have been desirable, but us budget sailors can always write pages of "wish lists"....

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