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Quick question about fuel return line

riseric

Well Known Member
Patron
With an intended fuel injected engine, I am aware that I'll need a fuel return line.

Is one return in one tank for the whole system the usual way to go or is there a need for a return line in both tanks?

I want to order the correct amount of the needed parts soon...

If in one only, is there a prefered side, left or right??

Am I overthinking this??? :eek:

Thanks for your advice!!!
 
fuel return line is not required for all injection systems, just some. In fact, mine for example, using bendix fuel servo, IO-360

no return required.
 
You only need a return line if you're going to use a purge valve. The boost pump assembly sold by Van's or EFII has the return built in to the pump assembly. That said I ran my purge valve return to the right feed line that goes to the fuel valve with a check valve in the line to prevent fuel from running up the purge valve line. This applies only to the Lyc engines, I understand Subies and conversions need the return line.
 
Ok, so let's say an injected IO 360 Lyc from ECI or Aerosport for example, with an off the shelf "normal" fuel delivery pump/system does not need a fuel return line back to the tanks???

I just don't want to open the tanks later for this...

What is and why a purge valve???
 
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Purge valve lets you run cool fuel from the tank through the system up to the distribution spider. This is used when the engine is heat soaked from a short shut down such as fueling or passenger loading/unloading, and you plan to do a restart.

The purge valve is installed at the fuel distribution spider, in line with the hose coming from the fuel pump. You select either the run position, or bypass position as needed. Fuel will either go to the cylinders, or back to the fuel system.

The purge valve is also used to shut off the engine in an Airflow Perf setup.

As far as putting in a return line, it is easy to do while building, and you can just cap off the fitting if you end up not using a purge valve in your system.

Now, if you are looking at an electronic F.I., it may require a return line to each tank, switched with the same valve you use to select the tank.
 
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Ok, so let's say an injected IO 360 Lyc from ECI or Aerosport for example, with an off the shelf "normal" fuel delivery pump/system does not need a fuel return line back to the tanks???

I just don't want to open the tanks later for this...

What is and why a purge valve???

The ECI fuel injection system Does require a return system.

The Airflow performance can use the purge valve, but it is not required, the FM150 is designed for use without the purge valve and the FM200 with the valve.
 
In the RV world, there's really only one fuel injection system out there that really must have a mandatory return line system that dumps back into the selected tank you're feeding from... and that's the ECI system. It's a lot like the old Continental system that was used on many older Beech Debonairs and some other planes. It has a constant return flow, and needs an expensive fuel selector valve (Andair duplex valve) that also has a second section to direct the return back into the feeding tank. We installed this system on my friend's RV-8 and it was expensive to buy, expensive to install, and finicky to get the initial calibration done, but once everything was set up, it runs fantastic and makes child's play of hot starts.
 
Need to study this more...

Thanks to all for your info!!

I thought this would get me a simple yes/no answer...

The lazy part in me likes Mike's suggestion of building one in both tanks while I'm at it and use plugs if not used later.

The efficient self is thinking why put something in there that maybe won't be used...

I must confess that I didn't study any sort of fuel system yet. Will have to do that soon!!!

As for the possible return line, I would have it dump the hot fuel into the second bay from the root, is this far enough?. Is it usually dumped at the top, middle or bottom of the tank? Or does it matter?

I love the idea of the purge valve for the hot starts. Another study item...

Never stop learning here and it's great!!!
 
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Purge valve lets you run cool fuel from the tank through the system up to the distribution spider. This is used when the engine is heat soaked from a short shut down such as fueling or passenger loading/unloading, and you plan to do a restart.

The purge valve is installed at the fuel distribution spider, in line with the hose coming from the fuel pump. You select either the run position, or bypass position as needed. Fuel will either go to the cylinders, or back to the fuel system.

The purge valve is also used to shut off the engine in an Airflow Perf setup.

As far as putting in a return line, it is easy to do while building, and you can just cap off the fitting if you end up not using a purge valve in your system.

Now, if you are looking at an electronic F.I., it may require a return line to each tank, switched with the same valve you use to select the tank.

Mike, Thanks a lot for the explanation, very usefull for me, too.
Val.
 
Thanks to all for your info!!

I thought this would get me a simple yes/no answer...

The lazy part in me likes Mike's suggestion of building one in both tanks while I'm at it and use plugs if not used later.

The efficient self is thinking why put something in there that maybe won't be used...

I must confess that I didn't study any sort of fuel system yet. Will have to do that soon!!!

As for the possible return line, I would have it dump the hot fuel into the second bay from the root, is this far enough?. Is it usually dumped at the top, middle or bottom of the tank? Or does it matter?

I love the idea of the purge valve for the hot starts. Another study item...

Never stop learning here and it's great!!!
I have the ECI fuel injection setup with return lines to each tank. I have the Andair dual valve with returns to each tank. However, unlike Neal mentioned, I had zero problems installing or 'calibrating' the valve. There actually was NO calibration at all so not sure what he was referring to. My experience was, install it and run lines to it. . . done. The valve was a bit more expensive than the normal Andair valve but worth the difference in price.

In reference to calibration I will say this about the return line installation in terms of calibration; I am running the GRT EFIS instrumentation. To get the fuel flow to register accurately required me to install two (2) red cube fuel flow sensors. One for the line running from the tank to the fuel pump, one from the pump back to the tank. There is a calibration for the EFIS to accurately reflect the amount of fuel being returned to the tank. For this reason alone I think it wise to run return lines to each tank if you intend to use any of the EFIS systems that monitor fuel flow.

The ECI plans I built from had me run the return line to the furthest most outboard bay of the tank along the rear baffle and through the Z-brackets. They have since changed that configuration and have a much easier install that has a fitting on the inboard access plate and running into the tank from there. If I were doing it again I would run the return to that access plate through a bulkhead fitting and then run a short tube through the top of the first rib into the second bay inside the fuel tank. It would be a much simpler installation.
 
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Return line

All good advice so far and I see that you are curious about various options for the fuel system.
If you have not yet done the tanks, I would definitely install a fitting in each tank to have all the options available when you do decide on the fuel system later in the build.
Simply install 1/8" NPT drain flange on the upper side of the inboard tank baffle
on each side. The same flange used for the fuel drain on the bottom of the wing. Having one of these will allow you to install a plug or later a return line if you wish.
As others have pointed out most fuel injection systems do not require a return line but you may want one if you know all the benefits of such a simple fuel system modification.
In my RV-10 I have a constant flow return line which allows me to use mogas without worry of vapor lock. In addition I can select the source of fuel and separately, the tank for fuel return. Only one fuel meter is required since the measured fuel is upstream of the return fuel. It adds a bit of complexity but a whole lot of options that others don't have when it comes to using mogas.
Don't worry about all this just install the flanges for now and leave your options open.
 
I have the ECI fuel injection setup with return lines to each tank. I have the Andair dual valve with returns to each tank. However, unlike Neal mentioned, I had zero problems installing or 'calibrating' the valve. There actually was NO calibration at all so not sure what he was referring to. My experience was, install it and run lines to it. . . done. The valve was a bit more expensive than the normal Andair valve but worth the difference in price.

In reference to calibration I will say this about the return line installation in terms of calibration; I am running the GRT EFIS instrumentation. To get the fuel flow to register accurately required me to install two (2) red cube fuel flow sensors. One for the line running from the tank to the fuel pump, one from the pump back to the tank. There is a calibration for the EFIS to accurately reflect the amount of fuel being returned to the tank. For this reason alone I think it wise to run return lines to each tank if you intend to use any of the EFIS systems that monitor fuel flow.

The ECI plans I built from had me run the return line to the furthest most outboard bay of the tank along the rear baffle and through the Z-brackets. They have since changed that configuration and have a much easier install that has a fitting on the inboard access plate and running into the tank from there. If I were doing it again I would run the return to that access plate through a bulkhead fitting and then run a short tube through the top of the first rib into the second bay inside the fuel tank. It would be a much simpler installation.

2 cubes not necessary if you install one cube between the servo and spider.
 
2 cubes not necessary if you install one cube between the servo and spider.
In my situation the cube(s) were installed on the cold side of the firewall. Perhaps they could have been mounted elsewhere but since that was the final location I chose, I had to install two. Your comment merits consideration for a new builder. Just something for builders to think about when they go to working out all the decisions on such things. In my case I chose the location I did for the purpose of isolating the sensor from excess heat and vibration it would have lived in had it been mounted on the hot side of the firewall.
 
fuel return line

Hi Eric,

Stop by and I can show you the purge system. I also have an extra andair fuel valve I can let go very cheap. :)

Mickey
 
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