-4 or -6 Return Line?

[DanH]

The SDS manual specifies AN-6 return lines from the duplex valve to the tanks.

However, the Andair duplex valve supplied by Vans (Vans part # FS 20x20-3) comes with 1/4" NPT upper ports and 1/8" NPT lower ports, which suggests AN-6 feeds and AN-4 returns.

So, either I run -4 returns, or find a source for the swappable port fittings so I can change them to -6.

What have other EFI users been doing here? Application is an RV-7A.

 

[FinnFlyer]

I would imagine there's only two significant factors here:
Fuel pump current draw
Fuel pump wear

And those factors (in addition to more or less restrictive return lines) are influenced by how much time you spend near full power compared to lower power and idle.

What does the restriction in the fuel pressure regulator look like?

Finn

 

[rocketman1988]

I used

I used -6 return lines.

You also may be in luck; I have a few -6 straight nipples for the FS-20 valve left over. I swapped them for elbows during the build.

Let me know if those might work for you...

 

[DanH]

I used -6 return lines.

You also may be in luck; I have a few -6 straight nipples for the FS-20 valve left over. I swapped them for elbows during the build.

Thanks Bob. Tell me about the Andair elbows. Are they internally curved or have some other flow advantage compared to AN822 elbows in straight ports? Or do they merely shave some width from the assembly?

 

[Paul Thomas]

The 2020 is listed on andair website as being 3/8 return but can be ordered however you want it. I'd imagine you can swap the fittings. Van must special order them that way.

 

[Ralph Inkster]

Would be better if the return circuit was -6, but I did a SDS conversion on a F1 IO550 with -4 returns & Ross OK’d it. Works fine.

 

[rocketman1988]

Thanks Bob. Tell me about the Andair elbows. Are they internally curved or have some other flow advantage compared to AN822 elbows in straight ports? Or do they merely shave some width from the assembly?

The elbows are NOT sweep elbows.

The only reason I changed from the straight ones is that it made the plumbing MUCH easier in my -10 tunnel, and yes, it shaved the width.

I have had no issues with the elbows.

Let me know if you want to try the straight -6s

 

[airguy]

I swapped the fittings and went with -6 on the return lines, I didn't want any backpressure.

 

[DanH]

Let me know if you want to try the straight -6s

Thanks much, but I'll need elbows in this application, thus Andair elbows or 1/4-NPT female.

Anyone stock Andair hardware on this side of the pond?

 

[[email protected]]

I did -4 returns on an SDS conversion over a year ago and it works fine.
on an 0-360 RV-6A
Art

 

[Mark33]

I did the FS2020 valve with the AN-6 supply and return lines.

 

[dmattmul]

Return lines

In the chemical process industry typical designs called for larger supply lines to the pump than discharge. Recently Andair came out with their FS2520 rated now at 300 hp (From the FS2020 at 200 hp) and the only modification, larger supply lines (AN8) same return lines (AN6). The issue is supply side suction is limited to what the pump can pull and cannot exceed (theoretically) - 14.7 psi where the discharge can exceed 100 psi (Have not looked at the Walbro pump curve recently) Cavitation is the killer of pumps. We would at times to correct an issue choke down a discharge to reduce the flow rate and eliminate cavitation until we could weld in larger supply lines. Getting liquid to the pump is critical. What the pump does with it just produces higher pressures that it is meant to pump. From memory the pumps used by both companies can easily produce 30 GPM at 40 psi, it's insuring the pump feed does not have much pressure drop is key. At elevated altitudes and lower vapor pressures of lower octane fuels only makes this worse but it's the supply side that is the issue. My guess is Ross for this application would be ok with AN4 output from the pump. If this was a 540 doubtful.

By the way Andair takes months (6 to 8) to ship a valve after you pay for it but can ship fittings the same week. I've known customers who received their new fittings in less than 10 days. Better to call them early our morning and talk to them than an e-mail.

 

[Mel]

Thanks much, but I'll need elbows in this application, thus Andair elbows or 1/4-NPT female.
Anyone stock Andair hardware on this side of the pond?

Dan, I also have 3 fittings left over from my current project. They are AN-6 and mount to the valve with 4 screws.

 

[DanH]

Dan, I also have 3 fittings left over from my current project. They are AN-6 and mount to the valve with 4 screws.

Thanks Mel. I'll need 1/4-NPT female if I switch.

 

[rodeja]

Thanks much, but I'll need elbows in this application, thus Andair elbows or 1/4-NPT female.

Anyone stock Andair hardware on this side of the pond?

Hey Dan if you end up ordering them, they come real quick. Not at all like the valve.

 

[TS Flightlines]

Dan---we use -6 supply and returns, and use the FS2020 valve with the Andair EF20 elbows, and not the NPT fittings with AN adapters. Space is the biggest reason. WE have the clients order this combination directly from Andair.

We use it on both the SDS and EFii duplex systems in all the airframes. We did one on Krea Ellis' RV10 with a Newton valve that worked out just fine.

Note---a little birdie said that a certain crazy little guy in SC was designing some fuel valves-------but you didnt hear that from me---
Tom

 

[DanH]

Note---a little birdie said that a certain crazy little guy in SC was designing some fuel valves-----

Darned good idea. In South Carolina, crazy little guys respond to email and answer the phone.

Break.

I'm gonna go with -6. This install is for another fella, not me, so I make it a point to stick with manufacturer's instructions. Ross likes -6.

I did poke around for some flow equations and calculators. The pressure drops for two equal lengths of tube at the guesstimated volume were surprising to me...like roughly 10x greater for -4 vs -6, potentially three or four psi. It's impossible to quantify accurately because of variations like how may 90's are in the flow, but -6 appears to make it a non-factor.

Thanks guys.

 

[rv6ejguy]

One more data point from just a few days ago. Customer working on atmo 550 Lancair said Andy Findlay used -4 for return in his racer- 120 GPH, worked fine so should be ok at a lower flow rate . Avoid drilled 90s if you can and try to use mandrel 90s if you have a bunch of them.

The orifice in the Borla FPR is around .180-200 IIRC.

 

[TS Flightlines]

Dan-----the ID of the AN side of this is .288. The ID of the flange side is .381.
We've used them exclusively on all our duplex systems, except the Newton Valve system we did for Krea Ellis' RV10.

Tom

 

[DanH]

One more data point from just a few days ago. Customer working on atmo 550 Lancair said Andy Findlay used -4 for return in his racer- 120 GPH, worked fine so should be ok at a lower flow rate . Avoid drilled 90s if you can and try to use mandrel 90s if you have a bunch of them.

Oy vey.......

 

[Toobuilder]

Keep in mind that the more fuel the engine uses, the less is returned. Get to a high enough GPH and the return would be zero. Or put another way, the highest return demand is with the engine at idle, and only diminishes with more throttle.

 

[Mark33]

I managed my plumbing little different from most. I “T’d” the fuel supply line into the return side of the FPR, so I’m immediately returning the unused fuel into the FPR and back to the tank(s), so I have dead-head fuel from the regulator to the fuel rail and injectors. This configuration works well and my fuel pressure stays very stable regardless of MP or throttle manipulation and I’m using AN-6 fittings throughout. The FPR is just basically bleeding off the unused fuel.

 

[DanH]

I managed my plumbing little different from most. I “T’d” the fuel supply line into the return side of the FPR

There are many possible configurations, all of which result in the same fuel pressure at the injectors.

Subject here is the return line, red in all the diagrams below. If it is too restrictive, fuel pressure rises at low flow rates, creating a potential for rich idle.

Break.

Mark, if I may, perhaps it would be a good idea to mount the regulator on a nice firm bracket. As pictured, you have a shaker (the hose to the engine) connected with a significant arm (the tee fitting assembly) to a mass (the regulator), which is suspended (again with significant arm due to fitting stack up) on aluminum bulkhead fittings. Set aside the use of aluminum bulkhead fittings for fuel, located above the exit where we can expect the highest temperatures given an engine compartment fire. As configured they are a questionable choice due to fatigue. Might run a hundred years, might not. A bracket would improve the odds.
.

 

[Mark33]

There are many possible configurations, all of which result in the same fuel pressure at the injectors.

Subject here is the return line, red in all the diagrams below. If it is too restrictive, fuel pressure rises at low flow rates, creating a potential for rich idle.

Break.

Mark, if I may, perhaps it would be a good idea to mount the regulator on a nice firm bracket. As pictured, you have a shaker (the hose to the engine) connected with a significant arm (the tee fitting assembly) to a mass (the regulator), which is suspended (again with significant arm due to fitting stack up) on aluminum bulkhead fittings. Set aside the use of aluminum bulkhead fittings for fuel, located above the exit where we can expect the highest temperatures given an engine compartment fire. As configured they are a questionable choice due to fatigue. Might run a hundred years, might not. A bracket would improve the odds.
.

Good eye, and thanks for the tip Dan. Yeah, I’ve ran it this way for about two years now without any noticeable problems, but it’s getting a little bit of a re-do and firming up as we speak. Like you said, it could work just fine like this forever, or could break tomorrow. That fuel supply line going up to the fuel rail(s) is secured to the engine mount, so there’s very little if any movement there. However, I’m still redoing the way I have the FPR mounted and firming that area up.

Also, in reference to your attached picture, mine is basically configured like “B”. That single fuel supply line goes up to a “T” which then supplies fuel to each rail on either side of the engine. In my opinion, by immediately returning the supply fuel “at” the regulator, such as “B” and “C” depicts, shortens and simplifies the return fuel side more so than other other configurations, which may help with reducing fluctuations in fuel pressure.

 

[scsmith]

Excuse the thread drift, but on Mark's set-up, I am a little concerned about the flex hose to the engine connecting with a swivel-elbow. Vibration and inertial loads can unscrew the swivel-elbow fitting. - unless the hose is clamped to a hard point a short distance away, like to an engine mount tube.

 

[FinnFlyer]

Excuse the thread drift, but on Mark's set-up, I am a little concerned about the flex hose to the engine connecting with a swivel-elbow. Vibration and inertial loads can unscrew the swivel-elbow fitting. - unless the hose is clamped to a hard point a short distance away, like to an engine mount tube.

Read post #24 again!

"That fuel supply line going up to the fuel rail(s) is secured to the engine mount, so there’s very little if any movement there. "