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[Opinion] Which fuel filter(s) and where to place them?

RVFan671

Well Known Member
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So I am trying to install some systems right now and have some questions and seeking inputs. Some key information about my plans are that I intend to almost always use non-ethanol mogas but I also want the capability to run fuel that contains ethanol. I think I've settled on dual electronic ignition (SDS CPI 2 is plan for now) and mechanical injection. I intend to install a (Newton) duplex fuel valve with return lines. I'm building all my lines out of PTFE AN6 including returns.

So what filter or filters should I use for my planned mechanical injection and where to place them? The plans are calling for a single AFP filter (74 micron) in the tunnel. This seems easy by just following plans but for those who have flying planes is it a nasty smelly mess each year opening and cleaning these up? I've got the access panels already installed so it isn't going to be terrible getting to it here.

But then I'm seeing where some are installing wing root filters (dual) which gives redundancy and supposedly less mess cleaning the filters. But here I am seeing a lot of tight bends on the AN6 and that gives me a little pause with the fact that I will not be running 100LL very often. Am I right to worry about this?

What about under the seat / near the gear legs where the lines go through the brackets holding the lines? Is this a good location? Is it hard to get into here each year for cleaning?

In the wing root and under seat example, I think I'm seeing more along the lines of 30 or 40 micron filters being used. What level of micron is required or preferred and why? Is mechanical injection happy with 74 and less change of clog compared to a 30/40?
 
So I am trying to install some systems right now and have some questions and seeking inputs. Some key information about my plans are that I intend to almost always use non-ethanol mogas but I also want the capability to run fuel that contains ethanol. I think I've settled on dual electronic ignition (SDS CPI 2 is plan for now) and mechanical injection. I intend to install a (Newton) duplex fuel valve with return lines. I'm building all my lines out of PTFE AN6 including returns.

So what filter or filters should I use for my planned mechanical injection and where to place them? The plans are calling for a single AFP filter (74 micron) in the tunnel. This seems easy by just following plans but for those who have flying planes is it a nasty smelly mess each year opening and cleaning these up? I've got the access panels already installed so it isn't going to be terrible getting to it here.

But then I'm seeing where some are installing wing root filters (dual) which gives redundancy and supposedly less mess cleaning the filters. But here I am seeing a lot of tight bends on the AN6 and that gives me a little pause with the fact that I will not be running 100LL very often. Am I right to worry about this?

What about under the seat / near the gear legs where the lines go through the brackets holding the lines? Is this a good location? Is it hard to get into here each year for cleaning?

In the wing root and under seat example, I think I'm seeing more along the lines of 30 or 40 micron filters being used. What level of micron is required or preferred and why? Is mechanical injection happy with 74 and less change of clog compared to a 30/40?
There is a low micron count filter in the servo itself. No need for anything smaller than 74 upstream .
 
My 2c, use the large AFP filter in the tunnel, 74 or even 100 to reduce suction losses, consider using larger supply 1/2 fuel lines for the same reason.
 
I've used tunnel mount (RV-14A), wing and under seat in my 10. (Started with wing and changed to under-seat) All three have their advantages and disadvantages.
Tunnel, fairly easy to get to but gets a little crowded with the electric boost pump or in my case pumps. Minimal number of added 90's but some needed.

Wing Root, as you mentioned more 90's needed and for me at least had to take off the top and bottom wing fairing to get good access. I was not comfortable just taking off the top wing root fairing to clean the filters. I run the slightly larger capacity Walbro pumps and was concerned with higher pressure drops possibly causing issues. Since the wing root fairing butts up fairly close to the fuselage one needs to be very careful not scratching the paint.

I ended up switching to under the seat after using wing root access. Takes all of 5 mins removing the seat stop sliding the seat back and then removing the 8 ? access screws to get access. Very easy. To capture any gas spill just place a paper towel under the cut-off valve and filter. I also changed my fuel cut off valves to something slightly more industrial. For filters I used the Andair stainless pleated filters (62 micron) Others have used the Holley stainless pleated filters and they are also very nice just require fittings to adapt to flare.

If you are looking for a duplex valve, I have a very nice Andair (FS 2020) never used (I was going to use it for the 15) shoot me an SMS.
 
There is a low micron count filter in the servo itself. No need for anything smaller than 74 upstream .
Do you have to clean this filter each year? I'm only familiar with my carb 360 so FI is new to me, hence my lack of knowledge about an downstream filter.
 
Which pumps are these? In your sig looks like you're running EFI so I was wondering if these are compatible to what I need to run for mechanical injection or not, and where you got them.


Any photos?


They are the Walbro GSL-392 and no you would not use these for mechanical injection but could use there BPM-1 that uses the Walbro pump (pretty bullet-proof).

I'll try and get the specs for the valve; they are used on midget racers in the US. Since they are mounted inside the cabin I wanted something a little more industrial.
 
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Do you have to clean this filter each year? I'm only familiar with my carb 360 so FI is new to me, hence my lack of knowledge about an downstream filter.
Yes, that should be cleaned every year. It is a last defense filter, so normally sees little debris, but can fill up quickly when things start to go wrong in the system. You should examine the qty of debris that comes out as that can tell you of problems brewing in your fuel distribution system.
 
74 is fine for the mechanical injection. A big element is better. Auto gas is pretty stinky compared to 100LL, so I'd be inclined to see if the wing root location is practical.
 
Any photos of the under the seat filter and valve set up?
Would there be any value to a belly access panel?
I'm just at the stage of riveting the floor ribs to the belly skin, so it would be "easy" to add it now, if helpful...

Thanks,
Brad
 
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Any photos of the under the seat filter and valve set up?
Would there be any value to a belly access panel?
I'm just at the stage of riveting the floor ribs to the belly skin, so it would be "easy" to add it now, if helpful...

Thanks,
Brad
This is a pic before final close-up. Shut-off valve can be safety-tied open. Takes 5 minutes to slide the seat all the way back. (Rear seat stop mod needed) I would not cut exterior access panels in the belly.

Screenshot 2026-01-28 195128.png
 
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