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The fuel injection fuel return issue


John Slade

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Chad robinson & I have been discussing fuel return issues in private messages. With Chad's permission I'm posting the discussion here in case anyone has thoughts, comments or suggestions.

__________________________________________________________________

 

John, I've pestered you with questions on your fuel system plumbing in the past, so I hope you'll tolerate another. I've been toying with ideas on various failure modes and it seems to me that the most critical with your layout is having the return solenoid fail and you end up returning to a tank you don't expect. If you're low on fuel you might not notice this with a balance shift in time to catch it.

 

What I was wondering is if there was a way to SIMPLY create a checks/balances mechanism for the return flow. Fuel pressure sensors can be expensive, so I hate to litter them about, but it might be a good solution if the return line has enough pressure near the tank to trigger a good indication. Or maybe a simple sight gauge with a trapped ball that would be pushed against one end of the gauge if fuel was flowing that way.

 

Have you given this concept any thought? Your system is extremely elegant in that it minimizes the parts involved, reduces the plumbing in the cockpit area, and allows a cross-feed, all things I'd like to do.

 

The only alternative I can come up with that keeps a mix of both worlds (I hate the facet pump idea) is to use the pumps to select the source, and use the plans fuel valve for the RETURN instead of the FEED. The manual valve would give you final control/identification of where the return goes. But I'd like to avoid this if I can address the safety issue.

 

Regards,

Chad

#1147

(Working on the instrument panel, and dreaming of the future)

I can be reached on the "other" forum http://canardaviationforum.dmt.net

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Hello Chad,

> I've pestered you with questions on your fuel system plumbing

Its not pestering. Its thought provoking. Thank you.

 

> seems to me that the most critical with your

> layout is having the return solenoid fail and you end up

> returning to a tank you don't expect.

I agree. Two issues here. Tank pressure and fuel starvation.

1. Tank pressure. My catastropic tank failure was due to a blocked vent in worst possible conditions - i.e. zero consumption, max cross return. This is very unlikely in any flight condition. Keep the vent free (I added a wire mesh cap) and I think we're safe from this one.

 

2. Fuel starvation

First prevention mode is pilot procedure. e.g. I plan to draw and return from the right tank most of the time during local flying. For long cross country I'll swap every hour, so this is the danger area. Obvoiusly I plan to keep an eye on fuel levels after the switch. This is drummed in habit anyway. Worst case I can think of is that I dont notice the crossfeed, the left tank goes dry and the right tank overflows from the vent. Engine quits. Emergency procedure item # 1 = switch on both pumps. Engine picks up again, and I have a full tank to fly home on. Can you think of a worse case?

 

> What I was wondering is if there was a way to SIMPLY create a

> checks/balances mechanism for the return flow.

I'd like to do something on this, but haven't come up with a good, inexpensive idea. My solution for now is to keep a damn close eye on it.

 

> Fuel pressure sensors can be expensive

Not too bad. I got one from Vans for < $100. You only need one on the left return, but would it register pressure on a free return?

 

> if the

> return line

> has enough pressure near the tank to trigger a good indication.

Right. I doubt that it would. Perhaps some sort of flow sensor.

 

> Or maybe a simple sight gauge with a trapped ball

Hmmm. The returns are hidden right at the back of the cockpit. You'd have to pipe the left return forward, then back again. Not a good solution. Need something that'll alert you automatically. I REALLY like my LED annunciator / voice alert system. Cheap and effective. Since you're designing you're panel, consider an LED annunciator top center built into the glare shield as I did. Take no space, costs $10 and is fun to do. (note: I have a recent picture of it in the camera. I'll post it shortly.) Also - I recently added a white print on clear tape label showing the failure items with car like icons for quick identification.

 

back to you're question...

> Have you given this concept any thought?

Oh yea, but I must admit that I'd moved on. I'm glad you brought it back to mind.

 

> Your system is extremely elegant in that it minimizes the parts

> involved, reduces the plumbing in the cockpit area, and allows a

> cross-feed, all things I'd like to do.

Thanks. Don't forget the redundancy issue. Redundant tanks, pumps & filters is nice. Few single failure modes.

 

> The only alternative I can come up with that keeps a mix of both

> worlds (I hate the facet pump idea) is to use the pumps to select

> the source, and use the plans fuel valve for the RETURN instead of

> the FEED. The manual valve would give you final

> control/identification of where the return goes. But I'd

> like to avoid this if I can address the safety issue.

This would work, but you're just as likely to forget to switch as you are to get a solenoid failure :(

 

How about a simple low fuel warning on the left tank? I don't have one, but they're not too expensive or hard to install. Put it at, say 1/4 tank. If the solenoid fails, AND you're running the left tank, you'll get a warning (voice in my case) before the engine quits.

 

Am I missing anything here?

 

> (Working on the instrument panel, and dreaming of the future)

Keep on dreaming. It's the journey, not the destination (says someone who's almost there).

 

Y'know it might be a good idea to move this discussion to a public forum (canardzone.com/forum for example). We might get some good thoughts, suggestions or possible failure modes we havent thought of. What do you think?

 

Regards,

Keep thinking. Keep asking questions.

John

I can be reached on the "other" forum http://canardaviationforum.dmt.net

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John Slade wrote:

>>I've pestered you with questions on your fuel system plumbing

>

> Its not pestering. Its thought provoking. Thank you.

 

=) Then I'll keep, ah, provoking you.

 

> I agree. Two issues here. Tank pressure and fuel starvation.

> 1. Tank pressure.

> My catastropic tank failure was due to a blocked vent in worst

> possible conditions - i.e. zero consumption, max cross return.

> This is very unlikely in any flight condition. Keep the vent free

> (I added a wire mesh cap) and I think we're safe from this one.

 

I agree. This is the sort of thing that could happen if a vent clogged anyway, even without this type of setup, so the traditional means of addressing it are still OK. Double-venting helps.

 

> 2. Fuel starvation

> First prevention mode is pilot procedure. e.g. I plan to draw

> and return from the right tank most of the time during local

> flying. For long cross country I'll swap every hour, so this is

> the danger area. Obvoiusly I plan to keep an eye on fuel levels

> after the switch. This is drummed in habit anyway. Worst case I

> can think of is that I dont notice the crossfeed, the

> left tank goes dry and the right tank overflows from the vent.

> Engine quits. Emergency procedure item # 1 = switch on both pumps.

> Engine picks up again, and I have a full tank to fly home on.

> Can you think of a worse case?

 

I'm not sure, but I'll think about it. The nice part of having to deal with a return is that you can so quickly purge/prime an air-charged system. Just get ANY fuel flowing and the pressure will drive all the air out in a second or two. You might be restarting instead of letting the engine restart itself, but that's not the end of the world.

 

I suppose one thing you could do to address this issue is draw as much as possible from the tank that requires the return solenoid to be energized. That way your failure mode has you falling back to the tank with more fuel in it.

 

To break this down, the instigators of a problem that I can think of are:

1. The solenoid fails into an unintended position.

 

2. The solenoid fails during a switch. Is this a break-before-make device? It would be interesting to know if there is some middle state where fuel can flow to BOTH output ports, or if fuel could flow to NEITHER. If the device jammed mid-switch (maybe a seal breaks and jams it?), making both sounds bad because you have no control over the return and it'll flow to the path of least

resistance. But breaking both is worlds worse because now you have NO return line. Your fuel pressure gauge, if you're watching it, should be an immediate indicator that this has happened, you'll probably start running rich really fast, and all sorts of bad things can happen. I guess the biggest danger is fire if your fuel system plumbing can't take the sudden pressure surge before you kill the pump, and sprays fuel into the engine compartment.

 

3. The solenoid becomes clogged. Does it have the same cross-sectional flow area that a manual valve has? If so, anything that would clog it should have been picked up much earlier.

 

So I suppose the worst case is a jam of some sort. To address this, it might be a good idea to have a double-pressure (80psi?) relief valve somewhere plumbed directly to one of the tanks. You can have this with a manual valve, too, of course, but you get warnings that it might be about to happen, and you can also jiggle it to see if you can get it into one or the other states.

 

Obviously, this only applies if the device is break-before-make.

 

>>What I was wondering is if there was a way to SIMPLY create a

>>checks/balances mechanism for the return flow.

>

> I'd like to do something on this, but haven't come up with a good,

> inexpensive idea. My solution for now is to keep a damn close eye on it.

 

I've been thinking about two things. First, I might try to get some fuel pressure sensors from a junkyard on-the-cheap. Instead of wiring those to actual pressure gauges, I'd just use them with a simple interface circuit (comparator, probably $0.50 of parts) to drive a logic level on/off output that could be wired to a warning light on the annunciator panel. That is, if a side is on and fuel ain't flowing, turn on the light. And vice-versa.

The second is the above emergency-return. Let me know how your solenoid works, because it may be irrelevant.

 

> Not too bad. I got one from Vans for < $100. You only need one on

> the left return, but would it register pressure on a free return?

 

Yeah, it would pretty much always register pressure, at least atmospheric. Most of the cheaper devices are "absolute". But a comparator circuit from a 555 timer or op amp is really easy to make, and could be used to create a level-set trigger that only turns on above a certain point.

 

>>if the return line

>>has enough pressure near the tank to trigger a good indication.

>

> Right. I doubt that it would. Perhaps some sort of flow sensor.

 

It's tricky. It might have enough just past the solenoid, for instance, especially if the diameter of the return line is small enough. The pressure drop wouldn't really start kicking in until you got close to the tank. For safety, I'd be putting this right after the solenoid, maybe even on a T from the solenoid's output port.

 

> Hmmm. The returns are hidden right at the back of the cockpit. >You'd have to pipe the left return forward, then back again. Not a >good solution. Need something that'll alert you automatically. I >REALLY like my LED annunciator / voice alert system. Cheap and >effective. Since you're designing you're panel, consider an LED >annunciator top center built into the glare shield as

> I did. Take no space, costs $10 and is fun to do. (note: I have a > recent picture of it in the camera. I'll post it shortly.) Also - > I recently added a white print on clear tape label showing the

> failure items with car like icons for quick identification.

 

I'd love to see the picture. Currently, I'm planning a somewhat special top/side-view annunciator to replace several devices. The design is to create a panel with a pictorial representation of the Cozy, and various pieces of information in their relevant locations. For example, I'd have a small RPM display right where the prop is. LEDs would show fuel pump activity, and these would be located in the wing tanks on the picture. You get the idea. It would be rather large - 4"x4" or so - and would consume panel space, but I think it

would be worth it. And since it would replace several instruments I think space won't be a problem.

 

The reason behind this is that my plane will be wired with CANbus, a

communications bus designed for automotive use and all sorts of critical communications networks. My annunciator panel will be a bridge between the primary and backup busses, so it will have access to all of this data (fuel pressures, RPMs, etc.)

 

> How about a simple low fuel warning on the left tank? I don't have

> one, but they're not too expensive or hard to install. Put it at,

> say 1/4 tank. If the solenoid fails, AND you're running the left

> tank, you'll get a warning (voice in my case) before the engine

> quits.

>

> Am I missing anything here?

 

No, that third piece is a good idea. I must not have been thinking straight - I'm going to have fuel-level sensing anyway. Might as well add this. You know, another interesting way to address this is a simple wet/dry sensor in the sump. If your sump starts running dry, you can start warning like crazy before you run into an actual outage event.

 

Still beats a header tank.

 

> Y'know it might be a good idea to move this discussion to a public > forum (canardzone.com/forum for example). We might get some good

> thoughts, suggestions or possible failure modes we havent thought

> of. What do you think?

 

Not a bad idea, I was just hoping to avoid another flame war. 90% of the responses to this (admittedly recurring) topic are "just use a header" or "just use a facet transfer pump". I didn't want to waste time on that. =)

 

Regards,

Chad

I can be reached on the "other" forum http://canardaviationforum.dmt.net

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Hi Chad.

Interesting stuff.

> I suppose one thing you could do to address this issue is draw as > much as possible from the tank that requires the return solenoid

> to be energized.

On a long cross country this would be good procedure. On short local flights, just use the fuel from the non energized side.

 

> 2. The solenoid fails during a switch. Is this a break-before-make > device?

I think I checked this when I got it, but I'll remove it and check again. This is important information to have.

 

> It would be interesting to know if there is some middle state

> where fuel can flow to BOTH output ports, or if fuel could flow to

> NEITHER.

right. I'll check and let you know.

 

> 3. The solenoid becomes clogged. Does it have the same

> cross-sectional flow area that a manual valve has?

Yes. It's pretty big. No problem there, I think.

 

> I've been thinking about two things. First, I might try to get

> some fuel pressure sensors from a junkyard on-the-cheap. Instead

> of wiring those to actual pressure gauges, I'd just use them with

> a simple interface circuit (comparator, probably $0.50 of parts)

> to drive a logic level on/off output that could be wired to a

> warning light on the annunciator panel. That is, if a

> side is on and fuel ain't flowing, turn on the light. And vice-

> versa.

Sounds like a good idea.

 

> I'd love to see the picture.

I'll send a link when it posts

 

> Currently, I'm planning a somewhat special

> top/side-view annunciator to replace several devices.

Sounds excellent! Sounds like a potential product!

 

> a simple wet/dry sensor in the

> sump. If your sump starts running dry, you can start warning like

> crazy before you run into an actual outage event.

How is that done?

 

> Not a bad idea, I was just hoping to avoid another flame war.

You won't tend to get flamed in the forum. People are much more open, and the "old ones" havent figured out how to access the new medium yet. :)

 

With you're permission I'll post our emails on this and see if we can get some useful input.

I can be reached on the "other" forum http://canardaviationforum.dmt.net

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>>Currently, I'm planning a somewhat special

>>top/side-view annunciator to replace several devices.

>

> Sounds excellent! Sounds like a potential product!

 

I've been tinkering with visual information to display. Some things like RPM are easily represented there. Things like fuel pressures/flows could be done that way too, but might be harder to "scan". But I also intend to include warnings such as gear up/down, etc.

 

>>a simple wet/dry sensor in the

>>sump. If your sump starts running dry, you can start warning like

>>crazy before you run into an actual outage event.

>

> How is that done?

 

About what you'd expect. You have a separate fuel level sensor in the sump, just not a complex one. A simple air gap capacitor, could be two sheets of aluminum with some insulating spacers, mounted about 2/3 up the wall of the sump. If there's ever air there, you're about to run out of fuel. A comparator, which again is all of a $0.50 circuit, could be used to trigger a logic 0/1 output to drive a warning light, buzzer, voice warning, or any combo of the three.

 

>>Not a bad idea, I was just hoping to avoid another flame war.

>

> You won't tend to get flamed in the forum. People are much more

> open, and the "old ones" havent figured out how to access the new

> medium yet. :)

>

> With you're permission I'll post our emails on this and see if we

> can get some useful input.

 

I'd be grateful.

 

Regards,

Chad

I can be reached on the "other" forum http://canardaviationforum.dmt.net

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<... I hate the facet pump idea ...>

You might want to revisit that notion. Examine it as rationally as possible with an eye toward risk analysis and management.

 

<... use the pumps to select the source, and use the plans fuel valve for the RETURN instead of the FEED ...>

Sounds like you have a pump for each tank. How do you access the fuel in the tank corresponding to a failed pump?

 

The issues that are most important to me are:

1. Minimize the plumbing (particularly valves), and have NO plumbing in the cabin if it can be avoided.

2. Have a simple, easy way to assure myself that late in the flight all the fuel in the airplane is in the tank I am drawing from.

3. Main pumps (and filters) should be parallel and interchangable - in case of failure, flip one switch and I'm back in business.

 

I am able to do ALL this with NO valves (electric or manual). Three toggle switches does the whole job (two main pumps and a facet pump). Fuel transfer from the Left tank via the Facet pump to Right (feed and return) tank can be easily automated to prevent the main failure mode (over filling feed tank). The only failue that renders fuel unavailable is failure of the transfer pump, and that would become evident while I still had plenty of fuel in the "draw" tank - plenty of time to divert.

 

Absent moving parts, there are no prominent failure modes. Fuel management is very simple and easy (periodically run the transfer pump for a minute or two (which can be easily [semi] automated).

 

KISS .... Jim S.

...Destiny's Plaything...

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Why not eliminate the faucet pump entirly?

 

T the return to both tanks.

 

The pumps will controll indepentant supply. The return will find it's own way.

 

This is completly pilot independant (eliminating fuel managment issues, a big killer) redundant, independant, stops over filling, lowers parts count, is simpler and weighs less.

 

Or did I miss a fail mode?

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<... Or did I miss a fail mode ...>

I think you did. You are presumably drawing from one tank and returning gawd knows where. How do you influence much less control where your return fuel goes? Late in the flight, been on top of WX most of the way, unanticipated headwinds, getting low on fuel. Which tank do you select? How do you keep the return fuel from going to the other one? How do you avoid crashing from fuel starvation 20 mi from home with 5 gal of gas in the unselected tank? Bottom line, you have no way ensuring that the fuel is where you need it.

 

<... double throw valve for 50 bucks ...>

Where you gonna get a duplex valve for $50? The cheapest one I've heard of was three or four times that.

...Destiny's Plaything...

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Where you gonna get a duplex valve for $50? The cheapest one I've heard of was three or four times that.

More likely 10 times that. BUT, dust picked one up for $50 I believe. I think he has mentioned his supplier several times before and actually mentioned this part in particular. It is a salvage part. I've seen the two of them he has. They are big, but they do the job.

Mike LaFLeur - Cozy MkIV #1155
N68ML
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Oh I see. You assumed we were running on one tank.

 

Both fuel pumps running, backups at the ready, so if one is lost there is no emergency.

 

Barring long periods in uncordinated flight one will have equal fuel in each tank. This also means we dont NEED to know where the fuel is. (this observation has nothing to do with weather or not we should)

 

If there is an event involving one system I now have split capacity in two redundant systems, naturly, without pilot input.

 

Sorry I was not clear.

 

Did I miss a fail mode?

 

P.S.

MT; Turns wont shift fuel. Uncordinated turns will. But I like the connection idea too. Acts like one big tank, which kind of kills the two independant systems idea. Independant is good for the just filled up a tank and dont trust it idea. I think one should test a new tank on the ground, but I never see that advocated. So I dont bring it up. So lets keep that between us.

P.P.S.

Incorrectly positioned fuel valves kill. If their is no valve, then no one dies of the valve.:rolleyes:

seriously tho... If a system can be redundant for emergencys and not need pilot input before hand, why not buid that. But I declare that off topic. Create a thread for fuel injection systems. This is just for return issues.

:rolleyes:

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<... run a thin open line under the fuselage, between the two tanks that balances the two systems like a water level ...>

<... Barring long periods in uncordinated flight one will have equal fuel in each tank ...>

More accurately, "... one would expect equal fuel ..."

 

Nice theory, but along with coordinated flight it presupposes exactly identical fuel paths, exactly identical air leaks in filler caps, etc. My Velocity has wing tanks gravity feeding into a 5-gal sump from which fuel is drawn to the engine. Starting with 25-30 gal each side, at the end of the trip, left to their own devices, there is a 5 gal assymetry that I can't do much about. Like, I'm burning sump fuel, the right tank is empty and the left tank has 5-7 gal in it that won't gravity feed into the sump unless I fly along in a full rudder deflection crab for a while to pile the fuel up against the side of the fuselage. I've been fighting this ever since I got the airplane. Some days it's manageable, some days it isn't. As far as emptying strakes evenly is concerned, gravity is not nearly as reliable as you have been led to believe.

 

If you do the math, you'll discover that a 5-gal assymetry can be caused by a very VERY small difference in pressure in the two tanks. Like about 0.03 - 0.05 psi. It doesn't take much of a filler cap leak to dump enough of the vent pressure to make a .03 psi difference between the tanks.

...Destiny's Plaything...

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Thats an interesting difficulty. I would see that as a fuel feed issue. I dont see it as a fuel injection return issue.

 

So assuming we can get fuel out of the tanks...

 

You have a strong point on the assmetrical flow.

 

Lets assume that the T will be lower than the "blowing fuel out" level by a margin. That way when one tank is near full the head pressure starts to kick in. This gives us a natural auto leveling action toward the top of the tank. Then we can get back to the point where we don't NEED to know what the fuel is doing. If there is an assmetrical flow we dont care. If it all flows to one tank (say Right) then when it gets to the point where is starts to fill to the T it will all flow into the left, due to the head on the right.

 

Did I miss a fail mode? Or are we agreed we don't need a faucet?

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Originally posted by LargePrime

Did I miss a fail mode? Or are we agreed we don't need a faucet?

I think you missed several. The issue with MY Velocity (and a number of others) is that gravity flow to the sump doesn't work well. Like I start with full tanks and as I'm flying along (with ball centered) one tank gradually empties quicker than the other. Usually the Right tank empties first (leaving 8-10 gal in the Left tank). The next thing, the sump draws down to where the low fuel warning comes on (Left strake still has maybe 8 gal). Low sump light means I've got maybe 20 minutes of fuel left, but nearly an hour in the strake that won't transfer. I went to 3 or 4 forums, listened to all the ideas, heard from many folks who had similar problem and had or had not been able to solve it. I managed to take the edge off it, but it did NOT go away altogether. In the chocks, the strakes will eventually even out flowing from one to the other through the sump like a water level (may take a number of days). In flight, that will NEVER happen.

 

You're right that it's a fuel feed issue. It does however, support the notion that a "T" (a gravity fed 7-gal sump is about a prominent a "T" as you are likely to find) does not assure you of symmetrical flow through both branches.

 

<... Lets assume that the T will ...>

Let's observe at this point that the math probably isn't being done and some details are falling through the cracks.

 

<... one tank is near full the head pressure starts to kick in ... natural auto leveling action toward the top of the tank ...>

My earlier post quantified your "head pressure". Five gal of fuel in a Cozy represents maybe an inch and a half of "head" which translates to about 0.03 psi "head pressure".

 

<... we don't NEED to know what the fuel is doing ...>

I'll regard that as an unfortunate choice of words.

A nearly (but not quite) perfectly sealed gas cap will dump several times as much pressure as is represented by 5 gal of "head" - leaving you with "... several times five gallons of fuel ..." that you cannot understand why it won't gravity feed, even though your "T" is "... well below ..." the fuel level in the tank.

 

<... If it all flows to one tank ... when it gets to the point where is starts to fill to the T it will all flow into the left, due to the head on the right ...>

You'd think so. But it doesn't always happen that way. Lots of folks thrashing their brains out trying to figure out why that just doesn't happen the way it should.

... and so forth ...

When we do the math, we discover how very small are the numbers we're dealing with and how it makes tiny influences and imperfections in the system that we don't notice and can't measure loom very LARGE.

...Destiny's Plaything...

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I am keeping a EYE on the Fuel Flow Issues.........

 

What we need on this forum, is a Tool similar to the "Experimental Panel Builder" Here: http://www.epanelbuilder.com/

 

But with "T's" and Valves, Fittings, and pieces of Fuel Line.....Any one know how to build such a site?

 

One could see, what the other is talking about, then expand on that idea.

 

Other than that, Keep up the chat. And take your time, I have quite a while, before I will need to implement this.

 

:confused:

Joseph@TheNativeSpirit.Net

I am Building a Jo-Z IV StarShip.

 

What Do YOU Want?

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Okay how's this...

 

Run fuel equalizing line between the lowest points of the tanks. Add pressure equalizing line between highest points of the tanks. Add check valves from each tank to sump. One line for fuel to the injector rail, one feed back to a T fitting and where the fuel ends up doesn't matter because both tanks self level.

 

Will that work? :D

This ain't rocket surgery!

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Originally posted by marbleturtle

<... Run fuel equalizing line ... Add pressure equalizing line ... Add check valves from each tank to sump ... one line for fuel to the injector rail .. one feed back to a T fitting ...

What is this going to do to your parts count? What manner of trouble shooting issues will all this raise? What might be the failure modes of all these check valves and equalizing lines and all? Will the check valves ALL unseat EXACTLY THE SAME when presented with .02 psi head pressure to equalize? What if the equalizing line just doesn't equalize? What do you start looking at with all those parts and components? Wish I knew.:(

 

<... and where the fuel ends up doesn't matter because both tanks self level ...>

Gawd I hope so. All this fuss and bother it ought to do somethin'! Just what is not clear to me at this juncture.:confused:

 

<... Will that work? ...>

Damned if I know. I've described as best I can how tiny infulences and assymetries generated really BIG problems for me and some others. I hope it works for you better than it did for me. Forwarned is forarmed.

 

Keep us posted on the results ....

...Destiny's Plaything...

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What do you start looking at with all those parts and components?

Parts Count?

 

Add two static fuel tubes, one static T return tube.

Subtract mechanical 3 way 6 port selector valve.

Check valves? I thought you were already using those so I threw them in the mix. I don't really see the need for them yet. I don't like the idea that they could stick closed.

What if the equalizing line just doesn't equalize?

One Wide Open tube between both sides for air pressure, one for fuel... laws of physics say it must.

I hope it works for you better than it did for me.

Well... this is not the system you have. :D At this point I'm not saying it will work. I'm looking for valid reasons why it will NOT work.

 

I am looking at this design because I plan on running a fuel injected engine and two standard tanks with a center sump tank. If I can toss out the 3 position 6 port selector switch running 6 fuel lines into the front cabin (or return fuel selector, or check valves to the sump, etc.) and simplify the system in the process, then I think its a design worth persuing. :cool:

This ain't rocket surgery!

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I know, I know, same story repeated and repeated, BUT, many are willing to plumb hot engine oil to a heater in the front near you peetses, high preasure air conditioning lines to the same place and don't want to use a simple double throw valve to controll the fuel, because of a few AN fitings and the remote possibility of a leak

 

the reason that the used double throw valves are so cheep from the salvage yard is that there is no demand for them, they just keep working and are rarely replaced, the items that have demand actually go for 1/2 new cost. My buddy bought a used prop control switch, elec controlled prop, for 75 buckos and a new one, available in a week was 150.00. the darn switch was 45 years old!

 

enjoy the build

 

dust

maker wood dust and shavings - foam and fiberglass dust and one day a cozy will pop out, enjoying the build

 

i can be reached at

 

http://www.canardcommunity.com/

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  • 3 years later...

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