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  #1  
Old 10-18-2014, 05:13 PM
riseric's Avatar
riseric riseric is offline
 
Join Date: Oct 2011
Location: Québec, CNV9
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Default Fuel system Schematics review

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:


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 !!!
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  #2  
Old 10-18-2014, 06:37 PM
N427EF N427EF is offline
 
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Posts: 1,564
Default 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.
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  #3  
Old 10-18-2014, 06:57 PM
Scott Hersha Scott Hersha is offline
 
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Location: Cincinnati, OH
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Default

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.
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  #4  
Old 10-18-2014, 07:07 PM
terrye terrye is offline
 
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Location: Vancouver, BC, Canada
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Default

[quote=N427EF;926168]
It's too bad no one makes a gascolator that is also a fuel filter.
[quote]

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.
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  #5  
Old 10-18-2014, 07:11 PM
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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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Last edited by Walt : 10-18-2014 at 07:15 PM.
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  #6  
Old 10-18-2014, 07:42 PM
rv7charlie rv7charlie is offline
 
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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
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  #7  
Old 10-18-2014, 09:23 PM
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DanH DanH is offline
 
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Quote:
Originally Posted by rv7charlie View Post
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.
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  #8  
Old 10-18-2014, 10:22 PM
rv7charlie rv7charlie is offline
 
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Yep; couldn't find the other stuff locally. Should I/we try to find the other?
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  #9  
Old 10-19-2014, 06:38 AM
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rmartingt rmartingt is offline
 
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Quote:
Originally Posted by Walt View Post
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.
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  #10  
Old 10-19-2014, 08:07 AM
Randy Randy is offline
 
Join Date: Jan 2005
Location: Sedona Arizona
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Default

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
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