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Fuel Filter

Scott Hersha

Well Known Member
Need some advice on where to find an acceptable fuel filter(s) for my new to me RV4. I have an O-360-A1A with a Sensenich prop. I just bought this airplane, and I?m in the initial phases of ?making it mine?. The airplane has two Phenix Industries inline fuel filters (Aircraft Spruce) mounted in the aft end of the center tunnel and angled upwards toward the fuel selector valve. These filters are fairly large - about 6? in length and maybe 1.5? in diameter, one for each fuel tank. I?m having unusual fuel flow readings from my GRT FF servo, and the fuel pressure also fluctuates some times. I think these rather large diameter fuel filters, mounted the way they are, are cavitating, allowing air to enter the system and collecting in these filters after drainback. Downstream of the filters is the fuel selector valve, electric fuel boost pump, Flo-Scan fuel flow transducer, engine driven fuel pump, and finally the carburetor. I would like to install a couple smaller inline filters in the cabin wells adjacent to the center tunnel, mounted horizontally, which would put them below the normal fuel level in the associated wing tank, one for each tank. I want to get something that is compatible with an aircraft O-360 installation and maybe has a bypass function in case of clogging. I would need a small cleanable filter with cylindrical stainless steel mesh filter that is no more than about 4-5 inches in length so they fit in the side compartments. Any advice, please let me know.

If anyone thinks there may be other issues, please let me know what to look for. I?ve checked all fuel line connections, thinking I?m sucking air from somewhere, but everything seems fine. These filters have not been in the airplane for long.

The airplane is almost 15 years old, has 285 hours on it since new, engine and airframe, and the previous (2nd) owner put 15 hours on it in the one month he owned it. I think he did the fuel filter(s) ?upgrade?. It runs fine, but the fuel flow has me wondering what?s going on. I can find peak EGT, but the fuel flow might fluctuate from .5 gph (@170 KTS!!) to as much as 13 gph.. fuel pressure sometimes get weird too. Makes me think there?s air in there somewhere, but I might be wrong.

If you can recommend a fuel filter replacement, or anything else, please let me know.

Thanks....
 
Scott
Congratulations on getting another RV. I am so glad to see you flying again.

Our Fish Fry Fly-in is this Saturday. Try to come over if you can.

Traci and I would love to see you and your wife again!!

Respectfully,
Darren & Traci Kerns
RV7 N599DT
KFRH
 
I use this one.

https://motorsports.flowezyfilters.com/?v=7516fd43adaa

74 micron

Series 3000

it is mounted upstream of the pump and fuel flow meter. fuel flow meter is downstream of the pump.

*******************

I suspect your fuel flow meter for the wacky readings.

I also suspect your airspeed indicator, 170 kts?

It should be 171 kts.
 
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If you have a look at the size of the hole all the fuel must pass through in the Fuel flow sender, you will understand why it should be downstream of the fuel pump. Sucking fuel through that small orifice is a much bigger problem than sucking fuel through the filters. Vapour lock will show up as loss of fuel pressure between the inlet of the fuel pump and the major restriction. So push fuel through the fuel flow sender rather than suck.

Fuel pumping issues will show up as low fuel pressure and fuel flow irregularities.

Bevan
 
concur

With Steve and Bevan:
A. The unit I used is about the same size as Steve's - getting any smaller for a rebuildable unit with low flow restriction appears to be unobtanium -as is any unit with a 'bypass'.
B. Flow meter needs to be downstream of your mechanical fuel pump, or readings will not be consistent. The flow/ pressure to the carburetor/injection system is what you are looking for - not elsewhere in the system.
 
Thanks Steve. I think that?s what I had in my first RV8. It might be a little too long to go where I wanted to put it (them - 2) so I will check. The current filters and whatever I end up with are upstream of the fuel selector, electric fuel pump, and fuel flow transducer on the cold side of the firewall.
Bevan - Not sure how I would mount the fuel flow sender on the hot side, downstream of the engine driven pump in my carbureted engine. I?ll have to look and see if that?s possible, but I think GRT recommends keeping the FloScan on the cool side.
 
Thanks Ben...... apparently it can, and should be put forward of the firewall, and downstream of the mechanical pump. I?m sure there?s a way. I?ll need a new fuel hose setup, which is fine since I was going to replace all the FWF hoses anyway. Good call.
 
Tom,
Not sure yet, I?ll be checking the planned setup soon. I?m currently involved in moving the pilot seat aft about 2.75? (big job), which involves several structural considerations. Should be done with that mod by this weekend and then it?s on to the fuel delivery setup/changes. I?ll be calling with an order for fuel and oil hoses for my RV4, including the new fuel flow transducer location. I?m sure it?s doable - only concern is two more fuel line connections in a hot engine compartment that could possibly leak. But that?s what I did on my fuel injected RV8 and it worked fine.
 
Ok, this fuel filter post has me thinking. My 7A has been flying since 2012. I can't remember anything about a fuel filter. Did I miss something. I'll go and have a look at the plane tomorrow. Is this something in the manual? If I don't have one, should I? I understand the purpose and all but can't believe I'd miss something like a fuel filter.
 
Summit Racing Equipment has a good selection of in-line fuel filters with AN connections in -6 and -8.
 
Dan,
That filter is similar to what I have now, and I have two of them - one for each tank, and the way they are mounted might be causing me some errors in fuel flow indications. Or maybe not. It might be just because of where the fuel flow transducer is located - upstream of the mechanical fuel pump, which Ben mentioned in an earlier post is in the wrong place. I was looking for a smaller filter to mount horizontally in a more convenient location. The two filters I have are Phenix Industries inline filters sold at Aircraft Spruce (among other places) and they are about the same size as the AFP filters you pictured. The thought among my KHAO RV buddies is that air can be getting into the mix because the filters are mounted on an upward angle near the fuel selector and high relative to the level in the fuel tanks. My plan is to redo all of that, and relocate the FF transducer downstream of the mechanical pump.
I purchased this RV4 about 3 weeks ago, and have a few things to fix before I start the big job - instrument panel upgrade.
 
Paul,
If you have a gascolator in your RV7A, you don?t need to also have a separate inline filter. The gascolator does the filtering...
 
Dan,
That filter is similar to what I have now, and I have two of them - one for each tank, and the way they are mounted might be causing me some errors in fuel flow indications. Or maybe not. It might be just because of where the fuel flow transducer is located - upstream of the mechanical fuel pump, which Ben mentioned in an earlier post is in the wrong place.

I flew with my red cube between the electric pump and the engine driven pump for about 600 hours, then moved it to the hose between the servo and the divider. The initial location worked fine at high flow rates, boost pump off, but the latter is much superior in terms of accuracy at low flow rates, or with the boost pump running.

The two filters I have are Phenix Industries inline filters sold at Aircraft Spruce (among other places) and they are about the same size as the AFP filters you pictured. The thought among my KHAO RV buddies is that air can be getting into the mix because the filters are mounted on an upward angle near the fuel selector and high relative to the level in the fuel tanks. My plan is to redo all of that, and relocate the FF transducer downstream of the mechanical pump.

I'd relocate the pump first.

There are RV applications with those filters horizontal, and apps with them vertical, per plans. Both work. Plus almost every filter traps a little bubble of air; look at a few of the glass or plastic ones, stopped or running. Doesn't hurt anything, unless an upstream issue is feeding air into the filter, and that's not the filter's fault
 
Paul,
If you have a gascolator in your RV7A, you don’t need to also have a separate inline filter. The gascolator does the filtering...

I prefer a fuel screen (70 micron or so) placed upstream of the electrical boost pump.
 
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