Fuel Filter Advice

[SWeidemann]

Kitfox Folks,

I'm looking for testimonials and field experience about fuel filters. What type & brand of fuel filter do people use and why? My latest favorite is the bronze filter element that can be installed in the engine compartment if desired (or anywhere else) and can be removed for inspection and cleaning, such as Earl's aluminum body with bronze insert. I have a technical bias against paper elements however they are being widely used. What do others use?

Thanks much,

Skot

[t j]

I have a finger strainer in each fuel tank and a 120 micron screen in my Aircraft spruce gascolator. That's all.

The Rotax 2 stroke installation manual says don't use paper filters. Use a fuel filter of 0.15mm (150 microns).

[HighWing]

I have glass fuel filters mounted in the down lines from each wing tank to the header tank. My lines run down along the top of the quarter window. The filters are visible as I fly and in low fuel situations as in long down runs from the Sierra crossing to home, I can visibly monitor fuel flow. I also have the finger strainers in the tanks. 900 hours on the first Model IV with this set-up and not a hiccup.

I do have one of the filters you describe, but it came with my second hand kit and it is still in the box as I like to see what is going on without taking things apart.

[Danzer1]

My preference is a combination of both Lowells and Toms.

I like the visibility aspect of Lowells and it provides the ability to supply fuel if one filter becomes clogged.

I believe a gascolator is necessary, but I do remove the mesh inlet filter as no need to filter twice.

A few other points to ponder:

Rotax recommends a 100 micron (.1mm) for 4 strokes. Most would find anything between 70 and 100 micron acceptable. Any finer and you are increasing the probability of clogging and the required maintenance un-necessarily.

I agree paper filters should be avoided - most are far finer than 100 micron and can clog much faster and trap water much easier. It is beyond me why places like Aircraft Spruce even sell them.

I would also never use a plastic or glass filter housing in the engine bay.

If using electric fuel pump(s) many have a pre-filter built into the inlet (ala 914 Pierburg pump). If you have an electric pump chances are it has one and it may be required by the pump manufacturer - it is another maintenance item.

If you have another type of fuel system - IE injected - follow the manufacturers recommendations to a tee. Many injectors require much finer filtering than a carbureted engine.

Incorrect filter micron selection/maintenance may be the cause of some rough running installations. How many even know the micron size of their filters?

All IMHO, YMMV!
Greg

[jiott]

I use the filter provided in the factory SS7 FWF kit for the 912. It is a NAPA inline filter in a metal housing, mounted at the inlet to the fuel pump per the build manual. Finger strainers are also include in the outlet of each fuel tank.

I personally don't believe a gascolator is necessary (neither does the factory) because you don't need to filter twice and the header tank with its drain at the lowest point in the system does the same job as a gascolator for water separation/draining.

[kitfoxnick]

My setup is very similar to Lowell's. I have two glass filters visible through the turtle deck. These filters can be taken apart and cleaned. I like being able to monitor the fuel and contamination level.

[Danzer1]

Hi Jim,


I personally don't believe a gascolator is necessary (neither does the factory) because you don't need to filter twice and the header tank with its drain at the lowest point in the system does the same job as a gascolator for water separation/draining.

I know there has been a lot of debate on this topic. I suppose you could use the header tank for separation - assuming you include it in each pre-flight check for water. If not it is useless for that purpose. The outlet is near the bottom and so it would be prudent to check/drain regularly anyway.

I also don't think the factory would be opposed to using a gascolator if a builder wanted to utilize one. As a point of reference - they are required in Canada.

I guess if you've ever gotten water out of a gascolator you'd be in the believer camp - I'm a believer! Of course if you don't have one, it would be hard to tell until potentially to late.

IMHO,
Greg

[jiott]

You are right, I include draining a sample out of the bottom of the header tank as part of every pre-flight checklist. I also agree a gascolator is not going to hurt anything as a belt and suspenders approach, but it is another maintenance point to deal with. If you have a gascolator, I believe you should still also drain the header tank on a regular basis because it will separate water and that water will lay in the bottom of the tank up to the level at which the outlet fitting to the engine is located (about 1"). This can be a lot of water and if it is not drained, it could suddenly overflow into the engine feed line and possibly even overwhelm your gascolator. I believe in the KISS principle and prefer to drain preflight samples in just the 3 spots-header tank and 2 wing tanks.

Some people say that a gascolator can be located at a lower point in the fuel system than the header tank, and I suppose this may be true on some airplanes. It also may be true on a tricycle gear airplane. Most of the water is going to separate during periods of sitting on the ground, and a taildragger like mine sits with the header tank drain being the lowest point, so I am very comfortable without a gascolator.

[Dorsal]

I also use the metal can filter and no gascolator,change the filter every 100 hrs.

[Danzer1]

I generally agree Jim, but a question - do you think its possible with a taildragger sitting, that water could collect in the aft portion of a wing tank (behind the drain) and then in a level flight attitude, make its way through the fuel system?

A few other points to ponder:

In the old days - don't know if still true as I can't find recent stats - somewhere between 5 and 7 aircraft accidents/incidents a MONTH in the USA were caused by fuel contaminated by water. Of those, about 75% were attributed to pilot error. IE: inadequate pre-flight.

So, I guess the point is - it really doesn't matter want gear you have in your craft, if you don't have a thorough pre-flight routine and stick to it.

As an aside, some may wonder why aircraft with electric fuel pumps AND a return line don't generally use gascolators. The fuel is flowing too fast for a separator to function and as such the water generally stays in suspension and diluted enough so as to still be a combustible solution. This however, does not negate the need to do proper a pre-flight of checking for water in each fuel reservoir.

Again IMHO,
Greg

Greg

[jiott]

Some good points Danzer, thats what is great about this forum. To answer your points: Yes water could collect in the rear of the wing tanks and be dumped into the system in level flight, but if that happened I believe it would be caught and trapped in the bottom of the header tank (providing there is enough room because you emptied it on your preflight) and could then be drained off at the next preflight. Unless there is such a large amount of water due to a long storage period that all bets are off and you really should have thoroughly drained all tanks in a level attitude before flight. I think any large amount of water that could overwhelm the trapping capacity of the header tank would also do the same to a gascolator. I also have a suspicion that the header tank may even possibly do a better job of separating water because it is bigger and the fuel flow turbulence thru it is less than in the smaller gascolator.

We are all just brainstorming here but trying to use sound engineering logic. As you say, a thorough and consistent preflight is still the most important thing of all, taking into account how long the aircraft has sat and in what conditions-outdoor, hi humidity, etc.

[Jerrytex]

I think you mentioned Earls. This and a gascolator is what I have. Cleanable/replaceable element

http://www.summitracing.com/parts/ear-230103erl?seid=srese1&gclid=CMvn1MinusICFYtAMgodeDQAOA

[Paul Z]

I don't clean mine, I replace once a year. Cheap insurance

[Av8r3400]

Personally I won't use a filter in the line from the wing to the header. Gravity flow is insufficient, IMO, to prevent premature blockage. So if you have a glass filter there and see the blockage when you are overflying the sierras, it's still blocked...

I have a gascolator with screen in my yellow plane and will be installing an inline metal filter pre mechanical fuel pump in my project plane. (Probably a similar napa model like supplied by Kitfox)

Many people don't know that there is an unserviceable filter in the mechanical pump on a 912. I don't know the micron value...

[Paul Z]

I'm between the per verbal Rock and hard place. I have an SLSA, and technically I need manufacturer approval to change it.

[Danzer1]

Larry,

I'm not following your logic - nor am I arguing your right to your opinion.


Personally I won't use a filter in the line from the wing to the header. Gravity flow is insufficient, IMO, to prevent premature blockage. So if you have a glass filter there and see the blockage when you are overflying the sierras, it's still blocked..

Pressure or lack thereof does not cause a blockage, although a blockage does reduce the flow. The reduced flow can be caused by a clogged filter caused by too small a micron filter and/or infrequent cleaning interval and/or really crappy gas very frequently and/or the wrong type of filter (paper) and/or incorrect fuel pipe size. There are thousands with this type of setup working in all types of high wing aircraft, not just Kitfox's.

100 micron mesh should be more than sufficient for any carbureted engine as there are no passages, openings or jets smaller than .5 micron (that I am aware of) in any carb.

Just food for thought,
Greg

[Av8r3400]

Let me try to explain my thought.

A filter located on the suction side of a pump has the fluid drawn through it via the vacuum of the pump. Quite a powerful motivating force. A dirty filter will reduce flow but takes considerably more contamination to stop the flow.

A filter that is using only gravity to motivate flow is much more susceptible to minor contamination of the element stopping the flow, because the motive force of the fluid is far less. This is especially prominent in the case of an aircraft, where inflight motion causes inconsistent tank to line orientation, at times dramatically lowering the gravitational force.


I like to mitigate risk. To me, the risk of the use in these filters is something easily eliminated.

[HighWing]

A couple more thoughts.

In the original design the fuel outlet on the wing tank was at the trailing edge. In the ramp position on a tail dragger water might collect, but it would be in tablespoon amounts. The port was then moved to mid tank to help mitigate the problem inherent with long descents with low wing tank fuel loads unporting the aft located outlet. I guess this is an instance of a solution to one problem possibly creating another.

Fuel filters mounted between wing tank and header tank would be before the low fuel indicator sensor. Problems with fuel flow from the wing tanks whether it is caused by kinked fuel lines, inadequate fuel levels or clogged filters would be indicated first by the lowering of the fuel level in the vent tube - I like the clear tubes - or by the flashing panel light which would typically give 20 to 30 minutes of reduced powered flight to find a place to put the airplane down. In the event of a post header tank obstruction, that fuel flow reduction would be indicated by a rough running engine or the dreaded silence. Time for putting the airplane on the ground would be a best guess.

[Paul Z]

I think you mentioned Earls. This and a gascolator is what I have. Cleanable/replaceable element

http://www.summitracing.com/parts/ear-230103erl?seid=srese1&gclid=CMvn1MinusICFYtAMgodeDQAOA

That is the same filter John McBean put into my SLSA. I have had no problems. I just replace one a year, which is probably overkill but that what I have been doing. I am concerned if cleaning it will really get the crud out. I can't see 35 micron particles.

[Danzer1]

Paul,
Are you sure it is a 2301 (35 micron) and not a 2302 (85 micron) - they look identical? Curious to know for sure what the factory uses!

Greg

[Paul Z]

Paul,
Are you sure it is a 2301 (35 micron) and not a 2302 (85 micron) - they look identical? Curious to know for sure what the factory uses!

Greg

I needed to replace the Filter because when I first started flying the plane I used Auto Fuel as marked on the Wings, I just didn't think about the detrimental effects of the Alcohol (Big Mistake), it started eating away at the tank or stripping out the mold release, and I had to flush my tanks, replace the hoses, clean out the air box, replace the filter, and rebuild the Carbs. I ordered a Fuel Filter from Kitfox. Kitfox sent me an auto fuel filter that was the typical auto in-line push on fuel filter, and it wouldn't work with my flanged inline mounting. I ended up removing the Fuel Filter, it had no labels saying what Model Number it was, it just had Earls Stamped on one of the Hex ends. I did a search trying to find the replacement. The only one I could find was Earl's Fuel Filter 230106, which is a 35 Micron. I have had absolutely no problems with the filter, never clogging. When I purchased it I figure if it works on a Race Car it should work on a plane, and it matched the Housing Size & Shape of the one I was replacing.

I did not realize, and did not find the 85 Micron filter, I guess I need to Call John and ask him which he would recommend using. 35 Microns is a significantly smaller than the 85 Microns. I'm going to drive to the airport and see if I still have the old filter in my tool box.

What are your thoughts?

35 Micron
http://www.jegs.com/i/Earls/361/230108/10002/-1

85 Micron
http://www.jegs.com/i/Earl%26%23039%3Bs/361/230208/10002/-1

[Danzer1]

Hi Paul,

As yours is SLSA, you need to stick with the factory recommendation, so best to check with them.

Personally, I don't believe anything below 100 micron is necessary as there are no parts, passages, ports, jets on any carb (that I know of) that are smaller then .5 millimeters (500 microns). Anything smaller than 100 would pass through and still be burnt in the combustion cycle. 1/10th of a millimeter is pretty dang small! As an a example: the thickness of a piece of #20 bond weight paper is about 1/10 of a millimeter. Anything much lower than 100 also increases your risk of premature clogging and hence more frequent filter maintenance.

IMHO,
Greg

[Paul Z]

Debbie, didn't recall she talked to either John or Judd and said it was the 35 Micron Filter. Like I have said I have never had it clog up. Even when I had the sludge in the fuel system it didn't clog it up.

[Danzer1]

Paul,

I just checked the SLSA brochure and it does say 35 micron, but I would check anyway as the same brochure also say it doesn't have a fuel pump and a 912ULS definitely has one - mechanical, but it is there - maybe they mean it doesn't have an "electric" fuel pump!

Greg

[Paul Z]

Only one Fuel Pump, on the passenger side of the engine. I just replaced it because of a recall. No electric anywhere I can find!

[Paul Z]

I think John needs a new flyer.
Here is the existing flyer from the Web. http://www.kitfoxaircraft.com/images/PDF/SLSAPDF/Equip-Features-SLSA-2014.jpg
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He's been pushing a Tri Gear or a Tail Wheel, here is my suggestion for change. I am having fun with my new plane. :cool:
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