Fuel Filter Placement?

[Scruffmeister]

I'm struggling with placing the fuel filter to my OS 55AX on my Wot4 Mk2 ATRF, the best I have come up with is shown in the picture below. Is this OK? The things concerning me are:

• How tight a corner can you safely make with the fuel feed to the carb?
   
• Does it matter that the tube is being raised above the top of the tank (the filter being the highest point)?

If anyone has any photos of "known good" installations I could see it would be very helpful.

(I'm running a two-line system for simplicity as not planning on fitting the cowl)

Thanks in advance.

 

Edited By Scruffmeister on 20/06/2014 21:16:38

[Adrian Smith 1]

The position is fine but I would shorten the fuel tube at both entry points into the filter by some margin in case the efficiency of the glow fuel flow is impaired. Hope that helps.

[Scruffmeister]

Thanks Adrian, but doing this will cause some fairly tight curve in the tube - so to the other part of my question, how tight a curve it OK for decent flow?

[john stones 1 - Moderator]

I would have a couple of filters on my fuel container...pump, and not use one on a model, Scruff

John

[Former Member]

[This posting has been removed]

[Myron Beaumont]

I fit a filter on the line to the engine from the tank just in case something comes from the exhaust pressure line into the tank .Then again I have another filter in the feed line from the main fuel bottle . Belt & Braces I suppose .Never had any probs anyway!

Thinking about it ,why dont I put another one between the exhaust nipple & the tank .Food for thought ?

Edited By Myron Beaumont on 20/06/2014 21:49:51

[Scruffmeister]

Thanks all - I actually believe that no in model filter could be a good option. Couple questions:

• Couldn't particles from the muffler pressure line could enter the tank and then the carb if there is no filter?
  
• Do you use a normal (unfiltered) metal clunk in your tank, or is your clunk actually some kind of filter (felt, etc.)?

Thanks!

[Myron Beaumont]

Scruffmeister

Cross post - we both thought of the exhaust/tank filter line .

[Scruffmeister]

I think the hybrid of one between the muffler and the tank (pressure line) is an interesting solution - as long as the fuel is filtered during filling this seems like a nicely closed system.

Does anyone actually run in this mode? Any reasons why it's a bad idea?

Edited By Scruffmeister on 20/06/2014 22:07:34

[john stones 1 - Moderator]

I don't use a filter at all on model, never have problems Scruff

I have one on pump line and one on line inside fuel container.

John

[namustang1a]

If your not using a slec tank you could use a filter clunk,(a sort of brass cone thing.

I tend to use them on 4/ as there int much room between carb and fire wall.

Ian

[Martin Whybrow]

I filter the fuel before the pump in the model box so the tank should be full of clean fuel; I also use a Sullivan double filter in the line between the tank and carb.

If you think about it, if there's enough junk in the fuel to block an inline filter, without the filter it will certainly block the needle valve.

[Rich too]

Posted by Adrian Smith 1 on 20/06/2014 21:28:15:

The position is fine but I would shorten the fuel tube at both entry points into the filter by some margin in case the efficiency of the glow fuel flow is impaired. Hope that helps.

Exactly, shorten and just run the tubing around the cylinder/engine case, it will be fine.

Rich

[Peter Miller]

No filter in the line, just in the filler. If it is in the fuel line it can get clogged and cause a lean run. Of course you can prevent that with a filter in the filler line but then you don't need one in the line to the engine do you?

I can never understand why people think that they are going to get crud through the line form the exhaust to the tank.

A) just what is going to come out of the engine that would be big enough to be stopped by any filter? Some fine black carbon? That is already in the engine and is not going to cause any damage.

B) THERE IS NO AIR FLOW FROM THE SILENCER TO THE TANK. THE TANK IS A SEALED SYSTEM. The total air flow through the line to the tank in each flight is the volume of the tank. For a 6 ounce tank that is about 160cc spread over ten minutes.

Now just what could that flow of 16cc of gas per minute carry up a line?

[Scruffmeister]

Thanks Peter and everyone else. That's very good information... I'm going to give it a try with no filters in the model - I'll let you know if it goes badly wrong but sounds like this is a perfectly well understood mode of operation!

[Engine Doctor]

Hi . You should use a filter as bits of dirt etc will get into and block carb . The best option I have found is the sintered filter clunk. It replaces the standard clunk and will not allow any air leaks etc . Also use one on the filler pump to pre filter the fuel when filling the tank. Ripmax and Dubro supply them .

[Braddock, VC]

A few observations, firstly most manufacturers of "quality" engines recommend an in line filter for fuel as well as two on the suction and discharge of the fuel filling pump.

Second the sintered clunk sounds like a good idea but if it's made of brass, if you use nitro in your fuel sooner or later it will cause corrosion on the brass bits, for this reason I wouldn't use one.

For the same reason I only use aluminium or plastic pipes in the tank. I had a run of corroded brass or copper fuel pipes where they passed through the rubber bung of the tank, pipes fractured and were covered in verdigris. I know someone will say but there are brass components in my engine's carbie, can't answer that just the voice of bad experience speaking. I suspect it's something to do with the cumulative effects of exhaust gas via the pressurisation from the silencer.

Third make the filter as accessible as you can, so you can check if there's a build up of crud, for all the filters in the world on your filling system won't stop you picking up bits of dirt or grass from the ground if you drop the filling pipe after you've filled the tank.

Finally, I always fit the filter the opposite way round to the way you have it in your photo, don't know why think it goes back to some dubro ones I bought which showed them fitted that way back in the year dot.

[john stones 1 - Moderator]

The filter in the picture is not a very good one to begin with. You have a clean tank and fuel lines, if you have a filter in your fuel container and your pump line, Why on earth do you need one on the model ? If its filtered it's filtered

John

[Former Member]

[This posting has been removed]

[Peter Beeney]

Whilst I would very much tend to agree with what Peter is saying, THERE IS NO AIR FLOW FROM THE SILENCER TO THE TANK. THE TANK IS A SEALED SYSTEM., some practical evidence does however suggest that there might be some slightly exceptional circumstances……

My own operational technique regarding fuel is pretty basic. After having had some aggravation with in-line filters in the early days I soon gave up on these. I still use an home made squeezy bottle for model tank filling and I just filter the fuel into the bottle through a piece of kitchen paper towel. There are no other filters. This has worked fine for me for many years. If there is any suspicion, though, that anything might have possibly found it’s way in anywhere it all goes back in the main container and is re-filtered.

Certainly on one occasion a while back some material, which I suspect were tiny pieces of carbon, (but not carbon dust), was finding it’s way into the tank and on from there into the needle valve via the exhaust pressure tube from the silencer. I poggered for a while about the reason as to why this was happening and eventually came up with a plausible answer, but the as to how it was happening might go something like this:

The expanding exhaust gases pressurise the air though the tube into the fuel tank and therefore it moves forward very slightly. Any foreign body in this air will move with it. When the exhaust pressure relaxes as the piston continues on the induction stroke the pressure in the silencer then becomes slightly negative so the air moves back again; but because this is not quite so vigorous the movement is not quite so far. Then this cycle happens all over again many times and thus there is slight but steady progression forwards. Certainly one stoke would not be noticed very much, but how many do you get in say half an hour’s running? At 10k it’s a 166 of them a second…

I soon cured my hassle with a filter in the pressure tube. Exactly as Scruffmeister has it in his photo. There is a small piece of metal mesh inside, and I cut a small piece of foam rubber to fit exactly in the larger compartment, no gaps but it’s not compressed either. This worked 110%, it stops everything getting through except clean fuel; or as in my case, clean air. In my experimenting with foam and fuel, the foam seems totally impervious to any methanol based fuels. If I needed to install a filter in the carb. line this is how I would do it, rightly or wrongly, I’m sure it would work for me. But it is amazing how dirt and hayseeds and anything else can sometimes enter what would appear to be sealed containers!

Methanol will attack brass components, sometimes quite quickly and aggressively. Hot rods and others that use methanol in performance cars and the like replace any brass in the fuel system with other material, but a brass and petrol mix is totally benign, hence the use of brass bits and pieces in carburettors for all time. Methanol is alcohol based, castor oil vegetable based, petrol, paraffin, diesel and mineral oil are mineral based. Nitromethane I believe is a derivative of nitric acid, there is a lot of oxygen in it, so it might well pickle ferrous metals to some extent; but as far as I’m aware, it’s not particularly harmful to non-ferrous materials or rubber seals etc.

In my case this was a one off - normally I never get anything in the tank from the exhaust other than exhaust gas. I’m sure the air does move slightly forward but not enough for me or anyone else to notice it.

PB

Edited By Peter Beeney on 22/06/2014 14:50:43

[Max50]

This is mine. Same as yours. OS 55AX. Works and fly's well with no problems. Also filters fuel going into the tank.

[Max50]

Forgot to say mines a WOT4 Mk3 with the 55.

[Steve Hargreaves - Moderator]

I'm with the filter it before it goes into the tank guys. I don't have an inline filter in any of my models....I can't remember the last time I had a carb blockage.

[Engine Doctor]

The sintered clunks are I believe made from bronze and are far superior to gauze or felt filters .They are also made from stainless steel but not for our use at the moment unless anyone knows differently. I fit them in all my models including the petrol jobs. My glow models use either 10% or 20% nitro . The ones in the filler tank show no signs of corrosion or green discoloration after some years of immersion so obviously no problem . Whatever the engine manufacturers recommend they dont fly the models that get air leaks in the fuel line and go dead-stick ! So its continued use of sintered clunks for me. As said aluminum pipe are a must these days as the modern brass degrades very quickly with our nitro fuel.

[YakMad]

I agree sintered clunks are the way to go, not only do they filter the fuel but they also stop air bubbles being sucked into the fuel line because of the very large surface area of the filter. OS make sintered clunks for their glow engines if you have any worries about corrision, I have never suffered corrision problems with any of the sintered clunks I have and I use alot of 20% nitro fuel. I also have a filter inside my fuel container which I use to fill the tank in the plane, I would never use an in-line fuel filter, I spent too many sessions trying to sort out blocked and leaking in-line filters.