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Old 07-02-2009, 14:56   #1
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newbee question? fuel filters

When you are looking for a fuel filter and there are different micron rating
what do they mean?

for example i have a dahl fuel system 100-m i think i know it is a 100 seizes on my boat, the filters come in
2 micron
10 micron
and 30 micron
are each of these used in different applications?
is 2 micron smaller the 30 micron or is 30 micron smaller the 2?
what would be the best for me?

i tried google but got nothing strait forward.
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Old 07-02-2009, 15:10   #2
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The numbers you cite refer to the porosity of the filter - the smaller the number, the smaller the porosity. Generally, you want the primary to be larger than the secondary, the latter is typically 2 micron. Search on fuel filters.
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Old 07-02-2009, 15:11   #3
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I am assuming you are using racor Spin on filters as a primary filter?

Normally your primary filter would be 30. Your engine manufacturer may indicate which if different. You have a finer secondary filter that is after this one. Using the extra fine filter on the primary really offers poor protection. It clogs up easily and all you need is to catch the chunky stuff. The 30 will catch more of it before the flow rate kills the engine. The 2 will stop the flow too qucikly and won't hold back as much as the 30 before it's clogged. The secondary filter is pretty small but when what you are filtering is less than 30 microns it does not require anything very huge. At about 5 microns most engines will burn up things that small and chuck it out the exhaust.

The more is better is often wrong. This would be one of those times.
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Old 07-02-2009, 15:17   #4
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my engine is a m25xpb, i have the dahl water separator for my primary that has a bowl and a drop in element and the secondary is a small universal screw on filter right on the engine right before the lift pump and fuel pump.
i dont have very much redundancy in my fuel system, would 30 micron still be what i wont
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Old 07-02-2009, 15:26   #5
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If it was my boat I would use a 10 micron primary and 2 micron secondary. Having a dual switchable primary is always good. That way if one filter plugs up you can switch over to the clean one.

This is just one of those personal preference things. I think it is better to clog the primary than the secondary as it is usually easier to replace and easier to monitor.
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Old 07-02-2009, 16:51   #6
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Quote:
Originally Posted by beetlejuice30 View Post
my engine is a m25xpb, i have the dahl water separator for my primary that has a bowl and a drop in element and the secondary is a small universal screw on filter right on the engine right before the lift pump and fuel pump.
i dont have very much redundancy in my fuel system, would 30 micron still be what i wont
is this good or should i add another in line fuel filter before or after the dahl?
OR
One other idea that i had was to put a T in the fuel like and install a racor 500ma for a second primary is there a better way of doing this the splitting the fuel line then splicing it back
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Old 07-02-2009, 17:05   #7
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You would need two Y valves, one on the input and one on the output of the filters so that you can completely isolate each filter. That will enable you to change a filter while the engine is running. Else one Y valve and you could switch filters but would need to wait until the engine was stopped in order to change the dirty one.

Do you have the Dahl ADF-11 filter? It looks okay to me. You could add another Dahl ADF-11 instead of Racor and then you would only need to stock one type of filter for the primaries.
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Old 07-02-2009, 17:10   #8
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dahl 100-m series takes dahl 101 element and the filters are hard to find and expensive

the flow rate is 40gph so i have a few options
the Y valves must be brass correct.
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Old 07-02-2009, 17:59   #9
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The Y-valve and any other fittings have to be fuel rated.
I can't find any reference to the 100-m series on the Amsoil web site, must be an older unit.

I think if I was doing this I would only use 1 Y-valve on the input, T the output and put a vacuum guage on the output line.

Have you priced the filters at auto supply places?
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Old 07-02-2009, 19:42   #10
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http://www.adiesel.com/Dahl.pdf
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Old 07-02-2009, 19:46   #11
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Just for reference
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Old 12-02-2009, 12:23   #12
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The micron issue is interesting and I certainly differ with our moderator. This discussion took place with a skipper of a new Leopard 40 cat several months ago. He stated the person from the factory who had placed a 2 micron filter in his primary was a moron. I told him he was looking at one, as my primary always carried a 2 micron. And I advised he do the same after verifying its use with several skippers and marine engineers (combined years of sailing well over 100 years and hundreds of thousands of sea miles) who had sailed extensively off shore and in remote places. The purpose of the primary filter is to take out the crap and if it works without slowing down flow to the engine then that is great - because when the stink hits you have some protection. I was off the coast of Venezuela running from a hurricane many years ago with no wind (calm before the storm) and big swell pushing us around and the engine stopped. I had clogged my filter. It took about 2 minutes to change it and we were on our way. I didn't have to work on the secondary (tricky to get at and harder to change, often requiring bleeding the engine) as it was fine - the primary got all the gunk. If the primary had been of a larger micron, then the secondary may have been fouled. When you are running hard on a lee shore you don't want to lose your engine and be forced to work in a cramped place getting bounced around a hot engine for several minutes hoping you don't hurl before you can get the job done and get out unscathed, and keep the boat in a safe place. I'd rather change out the small micron filters more frequently. The Leopard 40 requires the skipper to turn the rudder a certain direction and keep it there to access the narrow area to get at the secondary filter - and takes several minutes to change and he had to then bleed the engine; it's not user friendly. In big seas with potential for seasickness and the potential to get hurt it would be difficult. The primary on the Leopard was easily changeable, so why not use a smaller micron there? I finally called Racor and they assured me that the water separation issue, another question with the smaller micron in some forums, wasn't a problem. The tech at racor asked me where I was getting such faulty information - altho I suppose he might have a vested interest in getting us to use smaller micron filters so we have to change them out more frequently and buy more of them? Sailing off shore for 13 years and over 100,000 miles, I changed my fuel filters every 200 hours and only once had one clog - off shore in Venezuela. I had a gauge to tell me if the filter was clogging; but it never did. I never had to rebuild an injector pump or repair the injectors because of damage. I ALWAYS filtered my fuel via a baha filter into the boat and also had an Algae X on board in the fuel line. Experience (being the best teacher) on the part of the skippers at sea support the use of a smaller micron filter. Maybe the issue is different if you are cruising bays or coastal sailing.
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Old 12-02-2009, 12:40   #13
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Quote:
Originally Posted by karmaladen View Post
The micron issue is interesting and I certainly differ with our moderator. This discussion took place with a skipper of a new Leopard 40 cat several months ago. He stated the person from the factory who had placed a 2 micron filter in his primary was a moron. I told him he was looking at one, as my primary always carried a 2 micron. And I advised he do the same after verifying its use with several skippers and marine engineers (combined years of sailing well over 100 years and hundreds of thousands of sea miles) who had sailed extensively off shore and in remote places. The purpose of the primary filter is to take out the crap and if it works without slowing down flow to the engine then that is great - because when the stink hits you have some protection. I was off the coast of Venezuela running from a hurricane many years ago with no wind (calm before the storm) and big swell pushing us around and the engine stopped. I had clogged my filter. It took about 2 minutes to change it and we were on our way. I didn't have to work on the secondary (tricky to get at and harder to change, often requiring bleeding the engine) as it was fine - the primary got all the gunk. If the primary had been of a larger micron, then the secondary may have been fouled. When you are running hard on a lee shore you don't want to lose your engine and be forced to work in a cramped place getting bounced around a hot engine for several minutes hoping you don't hurl before you can get the job done and get out unscathed, and keep the boat in a safe place. I'd rather change out the small micron filters more frequently. The Leopard 40 requires the skipper to turn the rudder a certain direction and keep it there to access the narrow area to get at the secondary filter - and takes several minutes to change and he had to then bleed the engine; it's not user friendly. In big seas with potential for seasickness and the potential to get hurt it would be difficult. The primary on the Leopard was easily changeable, so why not use a smaller micron there? I finally called Racor and they assured me that the water separation issue, another question with the smaller micron in some forums, wasn't a problem. The tech at racor asked me where I was getting such faulty information - altho I suppose he might have a vested interest in getting us to use smaller micron filters so we have to change them out more frequently and buy more of them? Sailing off shore for 13 years and over 100,000 miles, I changed my fuel filters every 200 hours and only once had one clog - off shore in Venezuela. I had a gauge to tell me if the filter was clogging; but it never did. I never had to rebuild an injector pump or repair the injectors because of damage. I ALWAYS filtered my fuel via a baha filter into the boat and also had an Algae X on board in the fuel line. Experience (being the best teacher) on the part of the skippers at sea support the use of a smaller micron filter. Maybe the issue is different if you are cruising bays or coastal sailing.
I was almost willing to consider the argument until i got to the part about having an AlgaeX filter - Knowing the uselessness of this kind of constrains the basic premise about the credibility of the folks on whom you place your trust.
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Old 12-02-2009, 12:55   #14
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10 or 30 micron primary. With a brand new boat you could use a 2 I suppose, but 10 is plenty fine.
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Old 12-02-2009, 14:12   #15
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I agree that there is no information to adequately back up the use of an Algae X. I just noted that in was in place as part of the system. It was on the boat when I purchased it and I found no reason to remove it. My propulsion was a Perkins 6.3544 diesel, 1989 vintage, so the youth of the engine was not a factor in my case. And I am certainly not a mechanic so anything I could do to protect my engine was key in my decision making process. I was introduced to the 2 micron my a diesel mechanic with many years experience working in remote areas Canada. Most of his work was done on fishing boats and he learned the value of a smaller filter there. Once again, this is experience speaking. You have to look at your own situation to make value decision.
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