Fuel system options for fuel injection

[dust]

Are you going to have a valve to to fuel flow off?

[John Slade]

Each supply will have a manual shutoff valve for maintenance purposes only. This is not accessible in flight. The EFI fuel pumps has a check valve built in, and will not pass fuel unless power is on.

 

[Later note]

I added push pull cable control of the shut off valves.

[dust]

Although my friend absolutely hates fuel shutoff valves (never investigated a fire, but many crashes for lack of fuel flow on shutoff valves, the FAA requires them, will this setup pass?

[John Slade]

I'll let you know.

[Jim Sower]

John,

I just don't like the idea of a pump dedicated to a tank. It just feels creepy. The devistating failure mode of the original (all return to right tank) was kind of easy to spot. Thing is, I can't see any ADVANTAGE to dedicating a pump to a tank over having parallel pumps feeding the fuel rail. What do dedicated pumps buy you that you can't get from parallel pumps? OTOH, what do/can they cost you in the area of more serious failure modes?

 

With dedicated pumps, you lose the fuel in the tank served by the failed pump. How will a pump fail? If it tends to fail while it is running, you end up with a lot more options than if a pump doesn't turn on when you switch to it. Timing of a failure and the options (or lack of) it leaves you can be real important.

 

With Tracy's method, you have (pretty good?) (better?) options no matter when the failure occurs. I am very aware that I am really mind-f**king this thing. I'm just trying to make possible failures as benign as I can. I'm out of new answers.

 

How does Tracy's method substantially increase plumbing? How do dedicated pumps decrease plumbing and/or complexity?

 

Wish I had a nice tidy package for you .... Jim

[John Slade]

Jim,

>I just don't like the idea of a pump dedicated to a tank.

Strange. To me it makes more sense.

 

>can't see any ADVANTAGE to dedicating a pump to a tank over having >parallel pumps feeding the fuel rail.

I guess we all have our hangups. Mine seems to be redundancy.

 

>What do dedicated pumps buy you that you can't get from parallel >pumps?

What good is a parallel pump when you have a line leak and they're both sucking air, or if you have a line or vent blockage or contamination.

 

OTOH, what do/can they cost you in the area of more serious failure modes?

 

>With dedicated pumps, you lose the fuel in the tank served by the >failed pump.

True, but my engine will still be running while I find a place to put her down. Timing of a failure and the options (or lack of) it leaves you can be real important.

Timing is only a big issue if you're in a situation where all the fuel from the other tank is already gone. With a 1/2 hour reserve or better this should never be serious a problem. This is critical to you because you're so anal about getting to last drop of fuel.

 

>I am very aware that I am really mind-f**king this thing.

Its worth the effort. OTOH I think we've been around this circle a few times. There are pros and cons to every system.

 

>How does Tracy's method substantially increase plumbing?

It just seemed that way to me. Physical constraints made it hard to T the line before the pumps, then T it back again. The way I'm doing it now everything seems balanced, logical and simple. Its hard to explain, but this way just "feels right".

 

>Wish I had a nice tidy package for you

Well..., thank you Jim. Some other time perhaps.

 

Unless someone else has something new and constructive to add that hasnt already been said I suggest that we bring this thread to a close while I get on with the installation. My next post will include a parts list and pictures of the installed system.

 

But before I go.....

 

Just to confuse the issue I was at my local hydrolics supply store today picking up some AN fittings. The guy seemd to have everything so, to stump him, I asked for a small, lightweight, 12V normally open, continuous duty three way solenoid valve. Sure, he said, and plonked one down on the counter. $76. Body is anodized aluminum. It directs input to one port when energised, and to the other when the power is off. Cool. I think I'd better think it out again....

 

John

[niceez]

Big J,

 

I think I would want to know more about the valve and it's possible failure modes.

[John Slade]

You will. I'll be testing the s..t out of it and will report back.

As far as I know the main failure mode is that it doesnt energise. Result = return fuel goes to default tank.

[John Slade]

An update for anyone following the saga of my fuel system.

Everything is now installed. Pictures and installation details can be seen at http://kgarden.com/cozy/chap21b.htm

The solenoid valve draws about 2 amps when energized. It works as advertised so far. Currently the pumps and solenoid each have they're own switch, so I'm able to flip the fuel back and forth from one tank to the other.

Jim - you'll be pleased to note that with the wiring this way I can get at every last drop of fuel in the plane.

Unless anyone has any comments on the installation, the next update on this should be after I fly with it. Thanks to all for the interest shown and helpful input.

John Slade

[niceez]

Looks Good John,

 

I hope it works well and lasts a long time. I guess time will tell. I personally would like to know a year after you have been flying how well it works. I have some reservation about fuel filters after the pumps. I know auto's do it that way but they also have a sock filter in the tank just ahead of the inlet for the pump. I also realize you have screens in each tank but I am here to tell you "much stuff" will get by those screens. Would have also like to have seen a gascolator at the lowest point. Guess I'm old fashion but we just do things different in aviation. I'll get over it though if you have great success:)

 

-Dale

[John Slade]

Dale,

>I have some reservation about fuel filters after the pumps.

I'm told that for high pressure fuel injection systems using fine filters, its better to have the pump pushing the fuel through the filter rather than sucking through it. I'm keeping an eye on the filters and will monitor fuel pressure.

 

>Would have also like to have seen a gascolator at the lowest point.

I agonized over this one. I would have needed one on each side and there was no easy way I could see to put them ahead of the pumps without moving the pumps to a less ideal position. I was persuaded by the argument that there's so little fuel in the system that I'll be burning new fuel from the tank well before take-off. Secondly, I'm told that because of the glass tanks, EZ's rarely see water, even at the front fuel strainer and lastly - I have a backup system - the chance of water in both at the same time is slim. I'll also keep a close eye on this issue.

 

Thanks for the input.

John

[John Slade]

An update on my fuel system design....I discovered a failure mode that wasnt mentioned in our discussions and deserves serious attention.

 

Imagine this senario. You've forgotten to switch tanks during a two hour flight. You now have 30 gallons in one side and 10 gallons in the otehr. You also forgot to remove the vent cover on the full tank. You're on a long decent and decide to switch the return to balance the fuel load.

 

Guess what's going to happen. Scientists might say you create a vacuum. You're fuel pressure drops as the pump begins to suck on a vacuum, probably making the engine run rough, but the pump is powerful enough to keep pumping fuel. The tank (read airfoil) will begin to collapse under the negative pressure. After a few minutes you hear a craking sound as the composite sandwich fails, and the front part of you're strake implodes, totally destroying the airflow on one side.

 

Sound unlikely? Take a look at the attached picture. It happened to me, thankfully on the ground. I'm currently repairing the strake. The full story is at http://kgarden.com/cozy/chap21b.htm#collapse

See the entry titled "EFI Fuel Pumps Suck"

 

The fix:

1. Drill relief holes in you're vent / vent cover.

2. Put a screen over the vent to prevent mud daubers etc.

3. Make presence of vent covers in the cockpit part of the preflight.

 

Other than the fact that you'll have fuel starvation, I dont think this would be a problem with a central sump / gravity feed system. Just goes to show how you can introduce unexpected failure modes when you deviate from the straight and narrow.

[Tommy T.]

I don't know if you have considered this but Parker Mfg., maker of all different kinds of valves, fittings etc. make many different multi-port vaves, one of which is a six port specifically intended for use in fuel systems which require fuel return to same tank. Search Parker valves and send for a catalog which gives enough details you can evaluate any of their products for use. I used one of their three way on my Varieze in place of the killer plans valve.

[John Slade]

I hadn't heard of Parker, but I did consider an Andair 6 port valve. I didnt like the idea of running all those pipes up to the seatback. The expense was also a negative. How much are the Parker valves?

 

I like the idea of being able to draw from one tank and return to the other. This gives you the ability to draw on that "last drop" of fuel should the need ever arise.

[Tommy T.]

John, I think I paid $35 for the three port valve. I would think the six port is less than $100. T2

[marbleturtle]

... I may have just fallen off the turnip truck, but what about connecting the two tanks with a fuel line like a water level? Make it just large enough for fuel to tranfer but not so large that one tank "dumps" into the other in a slow turn. One side fails, the other still draws fuel by gravity. You loose redundant fuel supply in case of water fouling... but how much fowling effects one tank and not the other? Just a thought.

[Jim Sower]

John,

If your problem is dirt daubers or forgetfulness stopping up your vent system, there's a simple (and not too expensive) solution common in Velocitys. I have a low pressure check valve "T"d into my vent. As long as there is positive (ram air) pressure in the vent plumbing, the valve is closed. If the pressure in the vent line goes negative, the valve opens and the tank is vented to cabin pressure. There is a failure mode. If there is a sufficient vacuum in the cabin to implide the strake, you're in the same situation you describe, but you won't care as much The valve itself could be built for about $.15. Just take two pieces of different size neopreme tube and insert 1/4" of the little one into the big one. Get a cork or light weight sphere that fits loosely in the big tube and drop it in. Attach to the vent system. Gravity will seal the ball against the little tube. Just a little bit of suction will unseat it. If you want to splurge, small check valves are available all over for pocket change. Like automotive PCV valves, smog pump burp valves, and most likely skads of perfect solutions at McMaster-Carr

 

Just a theory .... Jim S.

 

PS We have a contract. Inspected the house last Friday. Came home to 18" of snow on the 250' driveway. More motivated than ever to "... get the hell outta' Dodge ...". Now, if some kind soul will just buy our house in the Catskills, we're off to Crossville.

[John Slade]

>but what about connecting the two tanks with a fuel line like a water level?

Not a bad idea, but if both vents are blocked you still have a problem, and I'd rather not complicate the system with any more plumbing.

 

Jim's check valve suggestion also has merit but, again, doesnt solve anything if the vent is blocked ahead of the valve. The valves also introduce new potential points of failure. However, I think this is may be the best answer. Where are the check valves on you're Velocity, Jim?

 

My inclination is to try to prevent and/or detect the original problem rather than engineer around it.

 

1. put a screen over the vent exit

2. drill a small relief hole an inch or so up the vent tube

3. make damned sure the vent covers are removed before flight

4. put an alert on the fuel pressure reading

 

Blocked (or covered) vents will surely cause a problem on any canard. Do any other canard drivers have thoughts or experience with this issue?

[Jim Sower]

John,

The vents on my Velocity start under the belly just forward of the firewall, go up the cabin side of the firewall to the top of the turtle back and back down the edge of the turtleback to the strake. The check valve(s) are at the top of the turtle back. As for your concerns:

 

<... My inclination is to try to prevent and/or detect the original problem rather than engineer around it ...>

I'm not sure I understand the distinction between preventing a problem and engineering around it

 

<... put a screen over the vent exit ...>

Prevents dirt daubers. Does nothing for memory lapses

 

<... drill a small relief hole an inch or so up the vent tube ..>

Defeats the purpose of ram air pressure in the tank. Will not help with a serious dirt dauber. You don't know how far in he will go, but you can bet it will be more than an inch.

 

<... make damned sure the vent covers are removed before flight ..>

Locate the vents close together, plug them both with a single unit, fasten a large banner to the plug and make "banner/plug in hand" a checklist item.

 

<... put an alert on the fuel pressure reading ..>

Waaaay too much fuss and technology. Pole vaulting over rat turds again

 

Blocked fuel vents will cause a problem on ANY AIRPLANE. The fact that we don't read a lot of problem reports indicates to me that there are simple, reliable, cheap solutions. We need only avail ourselves of one of these

 

Just a theory .... Jim S.

[marbleturtle]

>>but what about connecting the two tanks with a fuel line like a water level?

>Not a bad idea, but if both vents are blocked you still have a problem, and I'd rather not complicate the system with any more plumbing.

 

I was talking about the issue of fuel balance between the tanks in case the return line didn't equal out for the selection of both tanks. If you get both vents blocked, you're on your own.