Fuel Filters.

Garfly · February 22, 2016

Something Oscar said recently on another thread, gave me pause: "... paper filters ... should be bloody well outlawed and Gascolators be mandatory".

Fuel filters are a current topic on a (global) Skyranger forum and since it's of general interest, I've tidied-up the thread for easy reading and copied it below:

EXTRACTS FROM 'fuel filter' thread. YAHOO SKYRANGER forum. Feb.2016

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Can anyone suggest where in the UK I can get a suitable fuel filter (in between the fuel tank and fuel pump) for the rotax 912.

Thanks, Martin

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Try Flylight! http://www.shop.flylight.co.uk/skyranger-fuel-filter-482-p.asp

everything for your Skyranger / Swift / Nynja and many other types we can supply! Paul (Dewhurst of Flylight)

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Maybe in the UK you have to use some officially approved part? Is that so? Otherwise I'd say just go to any automotive supply and get any fuel filter that's size and fitting compatible.

The fuel coming out of the tank into the filter is at very low pressure and the fuel flow rate is very low (~4 gallons per hour) that any automotive filters specs would far exceed what's needed there.

There are simple inexpensive disposable types that just go in-line on the fuel line anywhere on the fuel line. After the fuel tank but before the first (auxiliary-electric) fuel pump. There are fancier ones that have cleanable replaceable ...sometimes metal... filter elements. I personally am a bit uneasy about the clear glass ones.... glass can crack.

We've been doing that (using inexpensive disposable in-line clear plastic disposable auto-supply store filters) on our Skyranger for years. We like that they're transparent so even on a pre-flight inspection at a glance we'd might if there was anything unusual in there.

We replace them every year at annual (with about 75 hours use on them) l, but frankly suspect that's overkill as we've never seen any indication that the filter we throw away has been clogged or compromised in any way.

My two cents., Alex

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We have had some trouble with filters over the years - paper element ones can clog up, and also the very fine purolator type automotive ones. Had an engine failure myself due to one of those and ended up in a field.

Lately ethanol has been an issue - causes the outer casing of some filers to soften and the ends can collapse leading to restricted fuel flow - TLAC posted a picture of such a one just today on Facebook. and some folk have had bacterial growth in unleaded fuel with ethanol leading to paper element filters clogging up.

So be careful out there and use what is proven and recommended - to avoid being overly experimental.

Paul (Dewhurst of Flylight)

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Using a paper filter can indeed be a serious issue. My son, while flying a CGS Hawk over downtown Cincinnati, Oh had a paper filter collapse shutting off the fuel and caused an engine out emergency landing. Minor damage to the plane and no injuries. The filter was a high quality filter with approx 25 hrs on it.  After his incident I switched to a glass filter with a replaceable inner screen on my Sky Ranger and change the screen at every annual. Don't know for sure, but suspect the ethanol blended fuel may have been a factor with the Hawk.   

Marlin

------------------------------------------------------------------------------------Interesting comments, i dont believe there is a mandatory spec that applies. The filters on skydrive and flylight websites look identical, but I cant see any details on their composition.

Scotty

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Page 87 of the 912 installation manual gives he spec for the fuel filter. .1mm / .004 in mesh size.

The mesh shouldn't be coarser than this or debris that can block carb jets can get through. Finer than this gives increased chance of filter becoming choked with fine debris.

The filters on Skydrive and our website are indeed the same - we buy from them. Until recently they were the UK Rotax agents so we had assurance the filters meet the spec.

Paul (Dewhurst of Flylight)

----------------------------------------------------------------------------------------------------Getting more educated on fuel filter from replies here on fuel filter issues, browsed a bit further and came across these items of info that raised questions that I wonder if anyone here can comment on:

From a more-or-less reputable source :

"...The Rotax supplied fuel pumps are actually automotive fuel pumps with both having a mesh filter inside them....."

Well, that raises for me two questions ....

(1) can anyone confirm that? And (2)if so, can and should THAT filter be occassionally checked, cleaned and/or replaced?

Also...I found a notice that was mainly about some specifically defective Rotax 912 fuel pumps that included this text:

"....accordance with the current Maintenance Manual LINE all mechanical fuel pumps have a 5 year life. Fuel pumps prior to 2008 (with S/N starting 07. or 06.) should have already been replaced in line with the routine maintenace requirements. If this 5 year replacement has been omitted the pump should be replaced with immediate effect. It is necessary to check the part no. & S/N of any pumps previously replaced to ensure that are not in the affected range.. "

Well, ours was not in rhe range of the specifically suspect pumps, but is over five years old.

Anyone know if that replace fuel pump every five years is a current recommendation?

(Discard a pump every five years _seems-, intuitively a bit excessive considering that in decades of car ownership, including some very old ones, i've never had a fuel pump fail, and given that in the plane, unlike the cars we have a auxiliary fuel pump ...But it's not terribly expensive and looks like it eould be a pretty simple job..So I'd be willing to replace it. Are any here replacing the pump every five years?)

Alex

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I might chance it in a car you can usually coast to the shoulder, in a plane you don't have as many options when it shuts down. I would contact Rotax or a distributer/ dealer directly they should know better than anyone , they have a vested interest in your engine , and your safety.

welderr

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When these automotive filters are fitted to cars, why do they not (in my experience) block? Are they fitted with ECU's that tell them where they are fitted?  

Kevin.

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its been a while since I was in the automotive industry, but it used to happen then from time to time - but very rare. Most modern cars have large cartridge type filters with many times the surface area of ours, so resist clogging better (but are much heavier!). they also are more regularly run which helps reduce fungal growth and are changed during routine servicing.

We also have the added problem of often using storage media like metal jerry cans etc. more opportunity for debris and water contamination. Most of the incidents I have had with restricted fuel flow is owner induced sh*** from dirty cans etc.

Paul (Dewhurst of Flylight)

OzBirdy · February 22, 2016

Im going to get shot down in a flaming hail of abuse for this post, but im go,n to post it anyway.

In twenty odd years, iv had one, only one forced landing coz of fuel starvation.

Since then, iv always filled my own drums, and transfered to the machine with my own drum pump, WITH FILTER.

And to realy rile the punces, the in line plastic/paper filter on the machine now is over 4 years old, and at a ruf calculation, has passed about 20 000L of premium.

At every 50hr service i flow check it, ( hasnt chamged since new) at 100 hours i drop the bowls and am yet to find a single passed speck. ( so its still functioning)

Its protected from UV and well insulated from all vibrations.

Ill soon be replaceing all flexable fiel lines coz theyv gon hard, but the filter will stay.

If it aint broke, dont fix it.

As is rit on the fuel cap of my CAT machinery, " use clean fuel, keep it clean".

Drum pump filters are mandatory here, and if your usen jerrys, NEVER drain all fuel into your tank.

Fire away.

Downunder · February 22, 2016

Got to laugh at the comments of "filters clogging up"!

Yeah, they're filters. They catch crap. That IS what they do.........

If they're clogging up, it means they are working and you should perhaps change it for a new one.... and maybe investigate the source of the (clogging).

Quality paper element filters these days are treated for resistance to alcohol/E85 and have resistant housings.

One thing that is very important is "free flow capacity". The gravity fed flow rate.

You want to be looking at about double the max engine usage. So if it is blocked 50%, you still have a safe fuel supply until it can be replaced.

What you should know about your filter:

Filter media type/material and possibly area.

Free flow capacity. GPM/LPM.

Housing material, eg nylon, PET, etc

Filtration rating, eg 100 microns ( 0.1 mm)

And of course, the inlet/outlet (barb) size. Matched to your hose size.

It seems to me, plenty of people know NONE of these things when purchasing a filter.

I personally prefer a smaller micron size (60 to 80) but only if the free flow rate is 200% my max usage.

Generally, the "free flow rate" decreases with a decrease in micron size unless greater media area is given or different media type used.

Which means you have a bigger overall filter.

I use a Mr Funnel, so fuel is pre-filtered into my aircraft.

Never seen anything in my on-board filters but still change them to be sure..

** All above my opinion only.....**

jetjr · February 22, 2016

I found it difficult to find a good quality replacement for auto types

All were unspec copies of racing types, most were for AN fittings, others were significant weight, no doubt for higher pressure usage

Finding small gascolator isnt easy either

I also discovered some plumbed upstream of boost pump which doesnt make sense to me. Pumps are very sensitive to suction restriction.

jetboy · February 22, 2016

The common advice years ago was that paper elements in open type microlights will clog with waxes found in the fuel - in a car not an issue but when fuel is colder it happens

On the Bantams i ran the choice was one of the OMC inline plastic filters from the marine supplies

These have a plastic mesh inside - not paper.

For the 701 the plans call for a gascolator I got the ACS one although the mesh is not the usual cylinder type like in certified aircraft just a flat circular mesh. Its been perfectly clean and running for 12 years - with a tubing replacement at about 6yrs. normally use avgas at the pumps but if gerry fueling I use Mr Funnel. Andair make a better gascolator/filter for the discerning. The less kinks and joins in a fuel system the better.

Heard so many bad stories about the inline filters which can be dissasembled - air bubbles leaking in, self dismantling during flight etc.

they sounded like a good idea

Ralph

OzBirdy · February 23, 2016

Thats odd?!?!

I was sure id get at least abit of flak from my post.

Not even a slap on the wrist.

Maybe you mob are more thoughtfull and understanding on this forum, unlike a few other forums.

Or you all just think, " wots the point, this blokes way beyond help." :)

jetjr · February 23, 2016

Well its your butt in he seat

I have seen a paper filter come to bits suddenly, not in aircraft, but paper went brittle and broke up clogging carb

Pretty sure rubber hoses have a time to replace. Its 2 yrs infromt of firewall. Thats maybe why some makers use other plastics as they can be run much longer.

skippydiesel · July 14, 2016

I use:

Hengst In Line Gauze Fuel Filters

Part No - H103 WK (90 degree fitting one end)

Part No - H102WK ( straight)

Both filters have:

8mm inlet/outlet spigots

An overall width of just 36mm

Overall length of 103 mm

Hengt claim a fuel filtration capacity of ≥ 2 µm (0.002 mm)

I have found these filters to have the following excellent features:

Clear body - for easy condition check

Very strong - in normal use it is just about impossible to break these beauties

Light weight - why add grams when you don't need to.

Leak free - unless damaged somehow, the fully sealed body cannot leak. I use good quality fuel injection hose clamps to ensure the push into hose fit does not leak or pull out.

Large Filter Area - very low fuel flow restriction/ less stress on pumps/ less likely your engine will experience total fuel starvation should contaminated fuel be inadvertently introduced to your system.

Long service life - assuming you are only using clean fuel in the first instance, these filter need only be replaced "on condition" however I would be inclined to replace them when you replace your fuel hoses.

Reusable - for the most part, with care & a little air pressure, most contamination of the filter can be removed. Why bother, they are so cheap, just replace them.

Cheap - I always carry spares in the unlikely event that I need to do a "field" replacement.

German Designed - made in Israel these filters are beautifully engineered and presented.

To be doubly sure that I am using clean fuel - I have a generic paper filter on my drum delivery pump and I use a filter funnel as well. I also carry a filter funnel in my aircraft the event of needing fuel away from home.

If you cant find any HENGST filters, I carry a small supply and may be able to help. S

Oscar · July 14, 2016

With respect to all contributors - my negative feeling towards paper filters is not because I've had any spectacularly BAD run with them, and I fully accept that many people use them very successfully. I've had a few, over the years, give me troubles in my cars/bikes, to the point where I always carried a spare. Most of the failures I had were due to bad lots of fuel - and if you've never had a bad lot of fuel, then I suggest you don't travel much in the more remote locations where (in days of yore, at least) the same fuel truck would carry petrol, diesel, and sometimes other stuff, to some small outpost..

I've had a plastic (Ryco-type) in-line filter crack, spraying fuel all around the engine bay. At the time that happened, I was running down a road (evacuating) with a bushfire nearby and approaching - and I think I possibly set the world gold standard time for replacing a fuel filter.. That's the sort of experience one does NOT forget.

Motor vehicles, generally, get frequent use so the sort of build-up of 'gunk' from older fuel sitting in the tank/s for some time rarely happens. Modern EFI systems require both high pressure and provide large flow rates with returns to the tank which - to a degree - will dissolve bacterial 'sludge' build-up. Those systems act to ensure that the flow-rate to the injectors is well above optimum. If you are running a 4-6 psi system ( Rotax carby versions and all Jabirus), there's no excess pumping capacity to overcome a diminishing flow-rate due to gradual restriction of the filter and it's been shown that the flow-rates in Jabirus (at least) can degenerate to levels that produce a dangerously lean condition for full-power use.

No doubt, every careful aviator checks the fuel after every top-up from the tank drains and on every DI. May I point out, that that check does in no way check the status of any paper/microsphere-type filter? And - for a top-up out somewhere remote, if sediment or other crap is present in the fuel, it may not have settled out to the tank sump when you do your check. A gradually clogging in-line filter has - by its nature - a diminishing area passing fuel, so less and less contamination is required to block the filter as time passes.

Every time you check the fuel coming from a gascolator, you effectively clean it ( and yes - that's not perfect, it should still be checked every 100-hourly at least).. BUT: if there's crap in your fuel, it will be pretty quickly apparent. I've added an ACS gascolator to our Jab. rebuild install, at a cost of a bit more than $100, from memory. It's a neat little unit and not very heavy, and I'll be flying with more confidence than using a paper filter that - IF it fails - will dump me on the ground.

I should add: the gascolator installation needs to be properly worked out, so it cannot contribute to fuel vapourisation if in the cowling area. But - we all know that a proper fuel delivery system is essential to our safety - don't we? We don't just trust to stuffing fuel in the general direction of the engine and hoping that it all works out OK - do we?

Old Koreelah · July 14, 2016

Oscar has any research been done on the frequency of gascolators rupturing/breaking during a prang?

I'd much prefer a sealed, replaceable plastic filter near the tank than a fragile glass unit in the hot engine bay.

Oscar · July 14, 2016

OK - I have no idea; certainly GA tends to prefer gascolators - I understand. Agree re any glass unit; a plastic unit in the engine bay would be a major fire hazard (and wouldn't meet any FAR requirement..), and I'm not aware of any glass-bowl gascolators - the ACS one isn't ( but also isn't all-steel, to meet FAR reqs. either..)

skippydiesel · July 14, 2016

1. Putting clean/filtered fuel in your tank is the only way to minimise the chance of a filter blockage.

2. Filters should, if at all possible, not be located in the engine bay (mine are located under the instrument panel).

3. All aircraft should be fitted with an alternate fuel supply in the event of the primary system failing (this system should have its own dedicated filter).

4. Filters should always be fitted on the upstream/tank side of pumps.

5. Gascolators are okay but a bit "old hat" when you can fit a modern high flow/gauze, disposable/low cost, lightweight, leak proof, filter & carry spares (which I have never had to use in 700 hrs)

facthunter · July 14, 2016

You could probably get a strong glass pyrex type bowl that would be as crash resistant as most fuel system components. Good paper elements are impregnated with plastic to make them more capable of handling moisture which make paper fall apart. Fine filters can block quickly. It's a sort of unknown depending on your fuel quality. Bacteria can stand temps of more than +50 to minus 60 in avtur. I've had large volume irrigation water hi flow filters that have to be backflushed every two hours or they end up with over 10 psi drop across the filter.. For petrol to a carburettor, you probably don't need a superfine filter like you need on a single rail diesel. Water is a bigger problem than fine particulates. Nev

skippydiesel · July 14, 2016

Hi Nev - I agree, that water is the most common contaminant of fuel. You sound like a person of some considerable (agricultural?) experience so you know, but many don't, that water can enter your fuel at almost every stage, from the refinery, bulk transport, fuel retailer, drums & your own fuel tanks. The fuel enters as the result of condensation, poorly fitting or faulty caps/lids, ground water seepage, (don't start me on the hygroscopic character of ethanol) etc etc. That's why we drain a sample from our fuel sump(s) before the first flight of the day and a little time after refuelling. Those of us who care about such things, keep sampling until no more water appears in the sample cup.

Avtur (aviation turbine fuel) - hmm not often used in small aircraft. Similar in may ways to automotive diesel that can be contaminated by bacteria. The bacteria can be controlled by good fuel hygiene (keeping water out), fresh fuel & a number of fuel additives that claim some efficacy. Appropriate filters will prevent entry to injector systems but the aim should be not to put contaminated fuel in your tank.

I am not sure of the relevance of an irrigation system (yes I know unfiltered water will block sprinkler systems and this can be a big pain in the A...). I have never been on the lookout for a suitable paddock to land in when operating a centre pivot or travelling irrigation.

I do not agree that it is safe to remove filters from the tank to carburetor delivery system of an aircraft (what you do with an earthbound engine is another matter) Even if you start with clean fresh fuel in your aircraft tank so many other contaminants can still enter your fuel system; compost tanks shed fibres, metal tanks & fuel lines have been known to deliver "swarf" & the products of corrosion, seals & gaskets can & do shed bits, paint flakes appear as if by magic and even highly rated flexible (rubber) fuel lines can shed the odd particle/fibre, even insect & plant parts have been found in fuel filters. I would rather keep all these things out of my carburetor/injector.

cscotthendry · July 14, 2016

My two cents worth:

If you own an LSA, you HAVE to use the filter designated by the manufacturer of your airplane. To do otherwise legally puts you in the E-LSA category.

In my situation, the filter is not available anywhere in Oz and I have to have them shipped out by the manufacturer. The part they use is an Audi/Volkswagen part, but is not carried by any dealers here is Australia. Grrr!

skippydiesel · July 15, 2016

Hi Scott

Not sure if this constitutes a "foot in mouth" observation but my aircraft is in the RAA 19 (kit built) category, which I believe means that it is essential an experimental aircraft. Most of these aircraft fly with the old metal & glass screw together filters - prone to leaks, heavy, bulky and relatively expensive (they do work & the filter tube/media can be cleaned or replaced).

After I found the Hengst type filters (there are other manufacturers but I believe Hengst is the only one with a clear body/casing) I discovered the aircraft maker specifies the same filters for their factory built version of my aircraft - happy coincidence.

Scott, if an alternative filter is available in Australia, there is no reason why you can not explain the situation to the manufacturer & request a written authorisation for the alternate filter. Of course they are not obliged to do so but most will, as long as the new filter meets or exceeds the specifications on the original.

cscotthendry · July 15, 2016

Hi ScottNot sure if this constitutes a "foot in mouth" observation but my aircraft is in the RAA 19 (kit built) category, which I believe means that it is essential an experimental aircraft. Most of these aircraft fly with the old metal & glass screw together filters - prone to leaks, heavy, bulky and relatively expensive (they do work & the filter tube/media can be cleaned or replaced).

After I found the Hengst type filters (there are other manufacturers but I believe Hengst is the only one with a clear body/casing) I discovered the aircraft maker specifies the same filters for their factory built version of my aircraft - happy coincidence.

Scott, if an alternative filter is available in Australia, there is no reason why you can not explain the situation to the manufacturer & request a written authorisation for the alternate filter. Of course they are not obliged to do so but most will, as long as the new filter meets or exceeds the specifications on the original.

Skippy:

Yes, I was originally told by the aircraft dealer that I could definitely NOT substitute BUT, today I spoke to him again and he is now saying that if it has the same root part number and the same specs then it can be substituted. All this happened after I posted. So yes, it seems you are correct.

BTW, not quite sure which bit you were referring to about the foot in mouth.

skippydiesel · July 15, 2016

Scott - make sure you get the authorisation in writing for your aircraft logbooks . You may also need to lodge a copy of the authorised modification with RAA.

facthunter · July 16, 2016

Just to clarify about filters blocking it's the fineness of the filter that causes the blocking I'm referring to. That was the reason for the backflushing in short periods in the example I quoted as the filters were fine "mesh", in that example, and very large in size (and cost).

I have never advocated removing filters unless to change them and It may have to be more frequently in some cases. We aren't trying to "refine" whatever is in the lines. We are trying to protect the engine and to make sure it keeps running in flight. If the filter can block quickly it becomes another hazard, which is apparently the case often. Nev

skippydiesel · July 16, 2016

Nev - All true.

I apologise for making fun of your irrigation example

In my humble fuel related opinion;

THE most important thing (after correct type/grade) is that the fuel you put in your tank should be free of contaminants.
NEVER assume that the fuel about to enter your tank is clean.
USE A FILTER FUNNEL (or similar devise) to make sure this is so.
Down steam (in line) filters will have very little work to do, if you just take the time to ensure the fuel is clean in the first instance.

facthunter · July 16, 2016

Yes that's so. Even the most perfect engine won't work without enough or degraded fuel. The high pressure pumps for single rail diesels, can't cope with impurities, particularly water even emulsified. Carby bowls should be examined for sediment too or a low part of the fuel line run flushed now and again, under pressure. My emphasis was that superfine filters can block quickly. The filter should be designed for the particular job and have enough capacity to cover normal ops and test (or replace) at intervals that cover the safety aspects of flying adequately. Nev

skippydiesel · July 29, 2016

Hengst, In Line, 8mm IN/OUT, Gauze Fuel Filters

Part No - H103 WK (90 degree fitting one end)

Part No - H102WK ( straight)

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