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Fuel system Schematics review

riseric

Well Known Member
Patron
Starting to seriously work on the fuel system, I offer my fuel system schematics to the brain pool here for comments/suggestions.

Keep in mind that it will feed a EFII system so full return to the tanks is needed.

Also, this is intended for Canada so 1 gascolator minimum is required.
I agree that in a fuel injection system, a gascolator is questionnable, but regs are regs...
I don't want one forward of the firewall nor in the cabin so I intend to install two, 1 in each wing root.

Here's the plan:
Fuel_System_Schematic_3__20141018.jpg


Two questions on top of the fuel schematic:
1- Instructions says to put a bead of tank sealant between the firewall and the forward side skins.
Would it be preferable to seal with 3M FireBarrier instead?

2-Would it be preferable to install steel fittings for the fuel lines through the firewall instead of aluminum ones?

Thanks !!!
 
Looks good to me

I am sure EFII has a diagram for a fuel system but if it was me I would put the filter before the pump.
It's too bad no one makes a gascolator that is also a fuel filter.
I know of your regs and at least you have your gascolators in the wing root.
My 8 had 2 filters,one in each wing root,

As to sealing the skin to the firewall bulkhead, the primary reason would be oil seepage into the cockpit,along with carbon monoxide and to some extent smoke.
Pro seal is perfect and even RTv could be used. 3m fire barrier is a bit much
For this application but others may disagree.

Most everyone uses aluminum fittings in the bulkhead and that is what Van recommends. FWF I would use steel in most fuel system applications, again opinions will vary and some would have you use steel and stainless steel braided hose for the entire airplane. Generally speaking, I would not deviate from what Van recommends, it has worked very well for thousands of RVs.
 
The EFII fuel system shows an (optional) pre-filter inline before the fuel pump module, as well as the 10 micron filter downstream. Looks good to me.
 
It's too bad no one makes a gascolator that is also a fuel filter.
The Andair GAS375 gascolators have a 70 micron filter element inside the bowl. The EFII FF-2 prefilter is 90 micron, so the Andair gascolator will have even better protection for the boost pump.

In general this schematic looks pretty good to me. Some comments:
1. I prefer a filter or gascolator that I can inspect (ie. drain) on each preflight. The Andair filters do this the EFII FF-1 10 micron does not. This is a personal preference.
2. I prefer a the final main filter (your FF-1) to have an internal bypass in case of clogging. Again, this is personal preference. The injection servo typically has a screen on the inlet port, but this is not intended to be a final filter. I know, I know, if the final main filter is so badly contaminated that the bypass opens, the servo screen won't keep the engine running much longer.
3. I am using a steel AN fitting at the firewall because of it's higher melting point and greater fatigue resistance.
 
Does the electric fuel pump run all the time? The reason I ask is a 10 micron filter is pretty fine and would likely cause a pressure drop across it, not a good thing if only sucking with an engine driven pump in hot weather, (can you spell vapor lock).
 
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Bummer about the gascolator requirement.

You're basically talking about a 1st/2nd generation automotive fuel injection system, so...

A pre-filter is a good idea for gerotor/roller vane style injection pumps, but most injection systems expect to see relatively 'open' filter prior to the pump and a very fine filter after the pump to protect the injectors. Reason given is that a 'tight' fuel injection filter prior to the pump can actually cause vapor lock due to pressure drop between the filter & the positive displacement pump. See the large filter area 'sock' on typical in-tank pumps in current autos. The in-tank 'sock' is also very effective in shedding potential clogs, because the foreign matter isn't trapped in a filter housing; it just sloshes off with fuel movement in the tank. You can buy automotive 'socks' on ebay for cheap, or entire in-tank turbine pumps for not much more money.

The one thing I'd look at closely in that diagram is: what happens if the main filter gets clogged? Might be low enough risk to live with it. If not, a filter on the output of each pump with the filter outputs T'd together should minimize the risk. If the spec'd filter has a very high capacity (large volume prior to the element, and a large element), then the risk of a clog might be low enough to be comfortable with one.

I'd play with 3M intumescent caulk before you actually use it to seal the firewall to the skins. I'm considering it, too, but after playing with it, I'm less confident. It's very gritty. I wonder about it's ability to stick well and seal the joint (CO) at normal temps (not worried about the fire-stop abilities). It might work fine, bu I intend to experiment with it before actual use on the firewall.

Charlie
 
I'd play with 3M intumescent caulk before you actually use it to seal the firewall to the skins. I'm considering it, too, but after playing with it, I'm less confident. It's very gritty. I wonder about it's ability to stick well and seal the joint (CO) at normal temps....

Sounds like you bought the latex base home improvement store caulk. Wrong stuff.
 
Does the electric fuel pump run all the time? The reason I ask is a 10 micron filter is pretty fine and would likely cause a pressure drop across it, not a good thing if only sucking with an engine driven pump in hot weather, (can you spell vapor lock).

With the EFII setup there is no engine driven pump. The electric pump runs all the time; the second is there for backup. I don't think vapor lock is much of a concern with this system; it's designed to push fuel to the engine. I'm strongly considering it myself.
 
I have a dual pump EFII fuel pump module for sale in the classified section:) Robert sells good filters for before the pump and after the pump that work well for his system.

I also have a single Andair gascolator that worked fine for me firewall forward. I had it placed low enough that the drain fitting protuded slightly below the cowl. I eliminated the spring loaded drain fitting in favor of a plug however.

Randall
 
Yep; couldn't find the other stuff locally. Should I/we try to find the other?

Yeah, if you want to use it on your airplane. "Fire Barrier 2000+" is the correct sealant. Spruce has it, as do industrial supply houses on the net. Here's the Product Data Sheet:

http://multimedia.3m.com/mws/mediaw...E666666--&fn=3MFB_Silicon_Sealant_2000+_cg1.p

It also comes in an "NS" version, meaning "non-slump". Same material, more thixotropic.

Returning to the application discussed here, I'd probably use a thin fay seal of tank sealant between the skin and firewall flange as instructed, wiping away all I could see after assembly. Later I'd come back and lay in a fillet of Fire Barrier 2000 as necessary to seal all the holes between flange tabs. If desired, a fiberfrax felt insulation layer can be installed under stainless foil, and the foil edge is buried in another fillet.

 
Fuel system schematic:

First comment is "use what works" meaning what has been proven. Your pump will be running at a constant pressure/flow rate, so it will be running at a higher fuel rate than you will use at a maximum engine demanded flow. This means you should pay attention to the pressure drop between the tank and pump inlet (measure it). There is no engine pump there, so if the electric fails you have no pressure. Automotive places the pump (or "a" pump) in the tank to reduce inlet pressure and there is a coarse filter there to protect the pump, and the fine filter (like yours) is downstream. If you had one in each tank, then you have some redundancy.

If you choose to keep the single pump, just be sure to measure the pressure drop from tank to pump with all piping etc in place. This will give you a idea of how much margin you will have for vaporization of fuel enroute.

Why? The recirculating system will heat the fuel in the tank, it is part of the process. Meaning - it will be higher than non recirc systems and should be considered in the vaporization margin.

Again - this is a suggestion with some basics, but use what has been proven with numbers.

Fireseal - I choose DanH, he HAS done the testing.
 
Gear pump and fuel valve

When I was Crew Chief on a Supersports racer and we put in the first SDS fuel injection to be used at Reno, I found a possibly unique problem. We used a very large positive displacement pump (geared) for the racing pump and a vane pump for backup. Fuel flow in the fuel rail was 90 GPH at 38 psi when the engine was off. At full power we ran 70" boost and over70 GPH equivalent gas and methanol.

When I put in the plumbing for the system and switched tanks the first time with the gear pump running (on the ground) the fuel pressure headed to infinity because the fuel valve return passage closed and the supply remained open in the valve. Blew the pressure sender and developed leaks where there were none!

Ended up with a relief valve in the discharge line plumbed back to the return line to one tank. Always hated it because if it did not reclose completely the engine would go very lean. Could not convince the pilot to use the vane pump whenever he needed to switch tanks, but the relief never malfunctioned while I was involved with the racer
 
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EFII fuel system

Gascolators are not required or desired with anything but a carburetor.
Our kits come with both a screen pre filter that goes before the electric pump and a 10 micron post filter that goes after the pump.
Please refer to our fuel system drawing in our installation manual.
This can be found linked on our Customer Area Page:
http://www.flyefii.com/customer_projects.htm

Robert
 
Thank you for all replies

I'd like to thank all that replied.

I know that these subjects can be a hot debate.

To summarize, my question about the tank sealant vs. the 3M Fire Barrier (the real stuff) was because I was concerned about fumes in the cabin IF there was a fire, even small, FWF. Tank sealant is great to seal out FWF fumes, CO or oil seepage but I doubt its heat or fire resistance???

Dan, your suggestion pleases me, thus I will go that way.

The steel vs. aluminum fittings. Everything going through the firewall like cables or wiring should be protected with steel or stainless steel pass-throughs. Why not the fuel lines? Especially if all fuel lines FWF are steel braided...

Robert, I studied thoroughly your fuel system diagrams.
I fully agree that a gascolator is of questionable utility in a fuel injected system. But I can't win the fight with Canadian rulings that require one, even with fuel injected systems...

Not wishing to have one FWF, or in the cabin, I think it best to put 2, one in each wing root. They have a 70 micron filter which will block any big debris from the tanks, fulfilling the mission of your 90 micron pre-pump filter. The gascolators will be reachable through the wing fairings for pre-flight drainage and their filters will be easy to maintain or change.

Again, many thanks for the suggestions and debate

best
 
Eric,

I put an Andair gascolator in each root, no filter in the cockpit. I also added a mini inline fuel valve (from Summit racing) at the Andair input so I may remove the gascolator's fuel bowl with a full tank of fuel.

Everything fits in the wing root including a return line.

Bevan
 
I fully agree that a gascolator is of questionable utility in a fuel injected system. But I can't win the fight with Canadian rulings that require one, even with fuel injected systems?
I am not aware of anything in the Transport Canada regulations and guidance material related to amateur-built aircraft that requires a gascolator. As near as I can tell, this gascolator ?requirement? was cooked up by someone in the Minister?s Delegate-Recreational Aviation organization.

It might be useful to find a type-certificated aircraft with fuel-injected engine that does not have a gascolator as part of the design, and point out to MD-RA that this was accepted by Transport Canada. Then politely ask them to provide a reference in the Transport Canada regulations or guidance material related to amateur-built aircraft that would require a gascolator on your aircraft.

If anyone can provide a suggestion for a type-certificated aircraft with fuel-injected engine that does not have a gascolator, I could dig into the POHs in our reference library to attempt to find evidence to substantiate this.
 
Call on Canadian fellow

Kevin, thank you for your contributions here in general and on this (gascolator) subject.

There are numerous posts and threads that can be found here on this Canadian, or should I say MD-RA "requirement". All mention the need to have one, carb or FI.

To follow on Kevin's offer, can I enroll all my fellow Canadians to put our ressources together and find a type-certificated aircraft with fuel-injected engine that does not have a gascolator?

If in fact such an aircraft exists in Canada, and with the help of Kevin it could be demonstrated that a gascolator is NOT mandatory, I'm pretty confident this "requirement" could be satisfactorily dropped.

What da y'a think??

(I did start a thread about this in the Canada section)
 
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Fuel system

I just finished my installation of the fuel system for my -10 using the EFII schematic. I installed a 100 micron filter in the supply lines that run beneath the seats and the post filter just after the dual pumps. Originally I had aluminum fitting through the firewall but decided to change them to steel, for piece of mind. Very clean install with the andair duplex valve.

I ordered the pressure regulator because I wanted to see how it fit on the firewall and was surprised at how small it was...

Robert over at FLYEFII has been a great help all along...
 
EFII reliability

The single ECU EFII systems are extremely reliable, however the majority of our systems go out these days as dual ECU setups. Customers tell me that they consider the redundant systems to be cheap insurance. I can't really argue with that.

We fully bench test everything before it goes out. All the parts in the system are the best components available. The wire harness is built very well. This has all added up to a system with an extremely good track record.
Robert
 
There is a relatively simple way to provide an emergency way to keep the motor running with an EFI system failure.

All EFI should have redundant fuel pumps and redundant power supplies. Therefore the fuel rail is guaranteed to be pressurized in any emergency. By tapping into the rail and going to a solenoid (redundant if you are paranoid) and then to spray nozzles in the throttle body, a set fuel flow can be assured. (Use two nozzles, one on each side of the throttle body to get even fuel distribution.)

The motor will run at a single power level and the pilot will have to find the right throttle position to match the fuel flow using EGTs. This would be done on the ground if possible or in early flight testing. The motor power can be reduced for landing by switching the solenoid off and on quickly.

We used this system in the Supersports racer I was involved with. Fortunately it was never used in for real. The SDS EFI was perfect the entire time I was involved.
 
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