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Tip: Electric fuel pump setup
Ok here is the text describing the installation and operation of Fuel sysytem.
The usual disclaimers.....This is how i did my system..I have no idea of your skills at creating your own system so I want it understood loud and clear that In no way accept any responsibilty for you attempting to do something similar.. I have an electric pump set in each wingroot with no mechanical pump. This was an attempt at providing a ?hydraulically correct? pumping solution for use with auto fuel, maybe even auto fuel containing ethanol. This system overcomes the potential issue with Vapour Lock by placing the pumps at the low pressure point of the system and also avoiding heating of the fuel by heat conducted through the engine block or by placement in a hot environment, namely on the engine side of the firewall. My system is for a FI?d engine, but a much simplified version can be used with a Carb by simply placing a Facet fuel pump in each wingroot. In this case no pressure reducing valve would be required. The carb version of this system has been running in my Zodiac for 500 or so hours and the FI?d in the RV7a for almost 300 without failure. FI'd system: Each pump set is comprised of a NAPA pump (Part #2P74028), Pressure relief valve from Airflow Performance, a filter (upstream of the pump), a manifold welded together from fittings from my local hydraulics shop (you can also find fittings to thread together, welding is a more compact way to achieve the same thing). A check valve (Andair from Vans) is placed inside the cabin in each feed line to the "Vans selector valve". Note even though I had QB tanks it was not difficult to plumb the extra returns to the tanks?I plumbed the pressure relief back to each tank, and the purge valve discharge back to the right tank. In order to fit everything in the wing roots I put flop tubes in both tanks?Oh Darn, guess I?ll have to do aerobatics now..:) . But you can imitate the same thing with solid tube if you really don?t want to hang in the harness. The selector valve uses the 4th port so it becomes a simple on/off valve. The two feedlines from each wingroot pump set join together in a Tee..directly below the on/off ?selector valve?. In practice the valve is never oprated. For TO and landing both pumps are run together, and tank switching is done by running the appropriate pump?Leaving the opposite pump off?Its dead simple in practice. Make sure each pump is wired independently!!! That means a separate switch and separate fuse/wiring for each pump?No muti function switches which would be a single point of failure. The two Andair check valves prevents cross feeding from one tank to the other. The FI system is all AFP but will work equally well where the servo is OK with constant fuel pressure. The following message will contain the pics. The only thing you can?t see is that I tapped out the ends of the fuel pump to 7/16ths UNF (for a standard #4 ORB fitting) this replaces the standard #3 ORB (at 3/8ths UNF)?.This is easily done on a drill press. Make sure to stuff some shreds of paper towel down the pump to stop shards of metal getting in the pump. My filters are the cheap paper kind (metal jacket) but I will probably replace those with a sintered bronze filter (Summit racing) if I have to switch to ETOH fuel. I also have a final filter in each feedline but to be honest this is overkill..well as long as a pump does not break a chunk of rotor of it is. Thats the basic system and I'm delighted with it. Frank Pics to follow |
Pics
[img=http://img370.imageshack.us/img370/2636/short115ws0.th.jpg]
Aww looks like it will only let me post one pic per reply |
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Don't even mention the multiple uploader...cus that didn't work either
[img=http://img301.imageshack.us/img301/2897/short121df7.th.jpg] |
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ZZZZZZZzzzzz....
I Could have welded up a new manifold faster than this..:)
[img=http://img301.imageshack.us/img301/7386/short124qm6.th.jpg] |
Thanks for the pictures--that looks slick.
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Hi Frank,
at the time you wrote this I was about to send you PM about details of your system. I wonder why this didn't get more comments even on other threads I've seen some interest towards your system -- which you flawlessly seems to promote. :D I didn't catch everything from the text/pics you wrote so I wish you would have time for some more details. Let others see what I've in my mind as well in case some others are lost as well. The engines (as I've said many times) are probably most weakest part of knowledge of building RV and therefore I'm keen to understand the choices and reasons why they are done. You said that you didn't have mechanical pump at all. Does this mean that either one of your electric pumps is running all the time? Do you have dual battery? If electric pump fails (pressure drops) does engine keep running until you have time to switch another pump on? As you have no mechanical pump I assume your only return to the tank comes from relief valve at the root of the wing? Just referring to the RV installation pictures of ECi engines at section 7.1 http://www.eci.aero/exp/RV6,7,9.pdf. Would you have similar plumbing diagram of your system? I didn't catch the fuel valve thing as well as pictures doesn't show them at all. As you say that it's practically not used at all so why have it in first place? But it is located between T-tie and throttle body if I've understood correctly. If one tanks runs empty and both electric pumps are turned on what goes to the engine (air or fuel)? which brand and model of engine did you have? You already mentioned that FI was AFP's. |
Answers
The engine is an IO360..A Mattituck to be precise...But to be honest the engine doesn't care...Both the AFP and the Bendix fuel systems are happy with constant fuel pressure and this is what this system provides.
Your right in as much as the electrical design of the pumping system is as critical as the plumbing...I.e the pumps must be wired independantly. I also have a duel alternator setup..I have an SD8 on the vacuum pad..Single Battery (My old carbed Zodiac used a dual battery with the same set up). Why is there a valve?...No other reason than to provide a placebo for the DAR..Well thats a bit harsh,..I would turn it off prior to crashing!..Other than that its not used. Its plumbed as an on/off valve..it is NOT a selector valve. The only return in practice is the return at the wingroots, except for the purge valve to flush hot fuel back to the right tank prior to a hot start..Actually works pretty well! What happens if you run a pump dry?..I don't know I've never done it..Nor do i intend to!..Those roller vane pumps use fuel as a lubricant so running them dry sounds like a bad idea. An airlocked pump won't pump air, simply because the pressure it will generate will be no where near what the opposite pump will do when pumoping fuel..I highly doubt you would get any air going to the engine. Remember you run BOTH pumps for TO and landing, the fuel pressure does not change if you run one or both pumps. The engine quits pretty instantaneously if you turn both pumps off, the Dynon alarms maybe half a second before everything goes quiet. Your questions are a little curious to me as I can't see how you would ever be in a stuation where both pumps are not running..The only unknown for me in flying this system is a freak lightening strike..I don't honestly know what would happen in this case. Yes one or both pumps are running all the time just as it is in your car.. If you were cruising along and the pump quit...so will the engine..But the engine will never stop turning unless you pull it up into a stall, so the enigine quits, flip on the other pump and carry on flying. If a pump quits on TO/landing you won't even know. Experience has shown that a full vapour return like that shown on the Titan engine is not required from a fuel vapourising perspective. Hope that helps. Frank |
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