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Go Back   VAF Forums > RV Firewall Forward Section > Fuel Injection Systems
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  #1  
Old 11-02-2022, 05:48 PM
SledDog SledDog is offline
 
Join Date: Nov 2010
Location: Lac du Flambeau, Wisconsin
Posts: 22
Default Airflow Performance Purge Valve Return Line Location

My Thunderbolt IO-320 arrived and has an Airflow Performance purge valve installed. I understand the need for the purge valve and how to plumb it for an RV-9A. A big thank you to Tom at TS Flightlines for answering my noob questions. Also, thanks Kyle at Airflow Performance. I am trying to find the best location for the purge valve return line bulkhead. From what I have read on the forum, higher is better to prevent fuel from flowing freely into the hot side of the firewall through a damaged return line. If you installed an AFP purge valve, where did you locate the firewall bulkhead?

Thanks for any information, advice, pictures, or general comments.
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  #2  
Old 11-03-2022, 12:21 AM
Bevan Bevan is offline
 
Join Date: Sep 2007
Location: BC
Posts: 1,736
Default

Quote:
Originally Posted by SledDog View Post
My Thunderbolt IO-320 arrived and has an Airflow Performance purge valve installed. I understand the need for the purge valve and how to plumb it for an RV-9A. A big thank you to Tom at TS Flightlines for answering my noob questions. Also, thanks Kyle at Airflow Performance. I am trying to find the best location for the purge valve return line bulkhead. From what I have read on the forum, higher is better to prevent fuel from flowing freely into the hot side of the firewall through a damaged return line. If you installed an AFP purge valve, where did you locate the firewall bulkhead?

Thanks for any information, advice, pictures, or general comments.
My return line firewall pass through fitting is located right next the other one that brings fuel to the engine which I believe is the Vans standard suggested location (lower center firewall near the fuel pump).

For better or worse, the other end in the tank is located at the highest forward point in the inner most bay. Not sure if this is best or the only way but itís what was recommended to me at the time and has worked well so far. 370+ hrs.

Bevan
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  #3  
Old 11-03-2022, 01:20 AM
rv8ch's Avatar
rv8ch rv8ch is online now
 
Join Date: Feb 2005
Location: LSGY
Posts: 5,009
Default

Same as Bevan - very close to where the fuel comes in on the firewall.


Quote:
From what I have read on the forum, higher is better to prevent fuel from flowing freely into the hot side of the firewall through a damaged return line.
Not sure I understand your concern about the damaged fuel return line FWF - that line only sees fuel flow at startup and shutdown. Take care to use good quality fuel line, route it carefully, support it where needed, ensure that it's on tight, and check the b-nuts regularly.
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  #4  
Old 11-03-2022, 02:05 AM
planenutz planenutz is offline
 
Join Date: Jan 2005
Location: Arrowtown, New Zealand
Posts: 86
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On my RV-6 I have the Purge Return pentrating the firewall at a position quite high on the right side of the firewall, just under the horizontal angle. I took the return line through the firewall then placed it parallel to the fuel vent line all the way to the tank. This allows you to brace the two aluminium fuel lines together for mutal support. Fuselage/Wing Root penetrations are beside each other, as are the tank penetrations.

As an aside - I ended up placing a decal on the instrument panel next to the fuel pump (and a second decal next to the fuel valve) recommending the right tank is selected for purging prior to hot starts. Reason - During the test phase I purged the system prior to a hot start with both tanks full to the brim with the left tank selected. Fuel in the right tank ended up venting out and made a bit of a mess. Not a huge issue... just something I'd not given a lot of thought to prior to it happening.
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  #5  
Old 11-03-2022, 09:07 AM
SledDog SledDog is offline
 
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Location: Lac du Flambeau, Wisconsin
Posts: 22
Default I think the bulkhead is below the fuel tank level.

Thanks, everyone, for replying. This is helping a lot. Here's my dilemma: I do not have a dedicated fuel return installed in my tank. According to Airflow Performance's installation manual, I should install a tee in the fuel feed line.

Here's the AFP schematic:


If I locate the return bulkhead fitting next to the fuel supply fitting (location 'C'), I think this will place the return line bulkhead below the full fuel level. If the purge valve return line or bulkhead is damaged on the forward side of the firewall, fuel could gravity feed freely into the engine compartment with no way to shut it off. Location 'B' may be above full fuel level. Location 'A’ is above full fuel level but creates a return line routing challenge behind the firewall.

Here's OP-32 and I have marked the three purge valve return line bulkhead locations I am considering:


Again, thank you so much for responding. I'm sure I am either over thinking this or just misunderstanding something. I'm also sure other builders have resolved this issue...if it is an issue.
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Last edited by SledDog : 11-03-2022 at 09:43 AM.
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  #6  
Old 11-03-2022, 12:02 PM
n816kc n816kc is offline
 
Join Date: Jan 2005
Location: Winter Haven, FL
Posts: 293
Default Purge tie in

I originally had mine tee’d into the fuel feed, found it introduced air bubbles into the system (at least that’s what we came up with) resulting in rpm surge when it happened. Changed it to the vent line and the issue went away. You can pump fuel out the vent with An overly long purge, but that isn’t necessary
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Last edited by n816kc : 11-03-2022 at 01:24 PM.
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  #7  
Old 11-03-2022, 01:48 PM
planenutz planenutz is offline
 
Join Date: Jan 2005
Location: Arrowtown, New Zealand
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As the purge retun is on the right side of the engine you would probably be better with something close to location A.

Using your picture, mine goes through the firewall below the "2" in the "VA102" printed on the schematic, but on the underside of the horizontal angle. This brings it closer to the vent line.

The reason I ran the line back to the tank was to get rid of the warm fuel and vapour so that fresh cool fuel can be introducted, avoiding recirculation of the hot fuel back to the engine. Adding a bulkhead fitting for this input into the tank was no hassle.
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  #8  
Old 11-03-2022, 02:02 PM
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Walt Walt is offline
 
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As noted above definitely better to run it back to a tank.
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  #9  
Old 11-03-2022, 02:22 PM
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rv8ch rv8ch is online now
 
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Perhaps add a valve between the purge valve and the connection to the return tank.

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  #10  
Old 11-03-2022, 03:14 PM
N427EF N427EF is offline
 
Join Date: Oct 2005
Posts: 1,696
Default return valve

A return valve is what I installed.
It solves your concern over a damaged fuel return line, I assume you are thinking of an accident scenario where your return line would uncontrollably spill fuel from the tank to a firewall forward location?
If you install a valve you can pretty much install that bulkhead fitting anywhere you please.
You can plumb your return fuel to either tank or both as in my installation.
I used Vans provided fuel valve for the return and an Andair for the supply side.
This approach also allows you to transfer fuel from one tank to another if you so desire.
If all you need is a return for your purged fuel, you can simply open the valve for purging and close it off after.
This set up is a great start if you later decide to use mogas and want to accommodate a constant flow return system.
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