Rotec TBI and fuelpump

[runbjo]

Hi all, I have a few questions regarding the design of my fuel system with a CAE 3300 and Rotec TBI MKII:

1) I know the TBI can run of gravity feed, but I would still like to have an electric pump as well. I have been recommended the Facet Posiflow #60245 http://www.facet-purolator.com/cat_part_finder.php. I have seen other builders are using the "cube type" version of the Facet pump. Please feel free to share experience and advice.

2) As for the design and layout, should I plumb the system with the E-pump in series with the engine driven one? Alternatively, install the E-pump in a paralell circuit with a check valve downstream to prevent backflow when switched of ?

3) The Facet E-pump has automatic pressure limitation and pressure range is only 1,5-4 PSI. Will a fuel return line (as with EFI systems) be required with this setup?

As always, your feedback is highly appreciated.

Kind regards

Rune Bjørkelid
www.flyfabrikken.com

[lpaaruule]

Hello Rune,

I'm no expert, but I can tell you some things I've heard, and what I've done.

I have a Jabiru 3300 with a Rotec TBI MKI. I wanted to install an electric pump so I could use it during takeoff, but otherwise just use gravity feed. I ended up using the engine driven pump in series with the electric pump for the following reasons:

1) Another builder suspected that during takeoff, the electric pump had too much restriction (when off) for gravity feed to supply enough fuel to the system. So, if the electric pump failed, the engine might not run well, or might stop.

2) At full fuel, there is enough fuel pressure with the gravity feed system, but as the tank empties, some have said the engine runs lean -- possibly too lean. Again the electric pump could solve this, but as said previously, what happens if the electric pump fails.

3) I decided that I wanted to run a vapor return line, and with that, you need some sort of pump running all the time.

4) I wanted the fuel pressurized to prevent vapor lock/ burps. This also requires some sort of pump to run continuously.

I haven't tested my system, but it is very similar to many non-Sonex systems out there except for my addition of the vapor return line. So I'm not re-inventing the wheel, or doing something unheard of. My vapor return line has a restriction fitting with a 1/32" hole. I didn't to go with a 1/16" hole as that would require too much fuel flow just for the return, so it's more of a bubble remover.

I'm using the cube type electric fuel pump. I'm going off memory here, but I think it will go to 6 PSI

I can't say that installing the electric pump in parallel with a check valve is wrong, but it adds to the complexity. I don't know what the added value would be to this. If you wanted to run without the engine driven pump, then having a check valve in parallel with the electric pump might provide a less restricted flow.

I don't think you'll need a return line from a pressure standpoint because the Rotec pressure regulator should be able to handle 4 PSI. If you were using the Bing carb, I think you would have had to limit it to 3 PSI if memory serves me.

Again, I haven't tested my fuel system yet, so my design may change.

[Brett]

I did this with my Aerovee fuel system,,, fuel pump and one way valve with gascolator on the other side. Use gravity except for priming and startup.

http://sonexboomer.blogspot.com.au/2016 ... build.html

[fastj22]

I have the Rotec, no pump, gravity fed, Jab 3300 and have no reason to install a fuel pump. It works just fine. I see no benefit to introduce more complexity.

[runbjo]

Hello all and thanks for your feedback and contribution to my discussion :)
I understand that there is different opinions on the subject of having an electric pump or not. Some would like to have one, and some get along just fine without. My reason for opting to have one is the added redundancy during takeoff and landing, and the occasional aerobatic manouvers. Still, optaining the added redundancy without increasing the complexity and introducing other portential sources of failure is always a balance act.

What currently seemes to be the preferred solution for my project is an electric pump in paralell with the engine driven one. We'll either buy a pump with a built in non-return valve or add one downstream of the pump. Further, I will also install a return line with a restriction fitting. This may prevent vapor locks. Size of restriction will probably be decided based on testing. Thaks for the tip on that Ipaaruule :)

Attached is a basic sketch of what I have in mind.

Kind regards Rune

[WaiexN143NM]

Hi rune,
Keep us posted on your progress. We installed a rotec mark 1 on our jab 3300 waiex. We did some flow tests on the facet electric cube pump installed, but it was too much restriction, so we took it off.we are running gravity feed with all lines firesleeved and insulated, and flying in the tucson heat. We've had a couple stumbles in the engine when coming back from a flight, parking at self fuel, then taxi back to hangar and engine got heat soaked. Never in the air.
We passed our set up and suggestions to john gillis, he hasnt had any trouble either.
Good luck!
WaiexN143NM
Michael

[fastj22]

Hello all and thanks for your feedback and contribution to my discussion :)
I understand that there is different opinions on the subject of having an electric pump or not. Some would like to have one, and some get along just fine without. My reason for opting to have one is the added redundancy during takeoff and landing, and the occasional aerobatic manouvers. Still, optaining the added redundancy without increasing the complexity and introducing other portential sources of failure is always a balance act.

What currently seemes to be the preferred solution for my project is an electric pump in paralell with the engine driven one. We'll either buy a pump with a built in non-return valve or add one downstream of the pump. Further, I will also install a return line with a restriction fitting. This may prevent vapor locks. Size of restriction will probably be decided based on testing. Thaks for the tip on that Ipaaruule :)

Attached is a basic sketch of what I have in mind.

Kind regards Rune

Your diagram is very similar to the one I drew up while waiting for delivery of my Rotec. I even have all the parts. But I decided to go simple first and just do the gravity feed to see if it worked. It did. So I decided to let it go through the winter and wait until the summer heat to see if it still worked. Got a few burps one really hot day so I put my burp tube back on, and haven't had a problem since. Go with what you want to do. Having fuel cycling through the system continuously will definitely stop the burps.

[sonex892.]

Hi Rune
I have retained the bing on the 3300. So it's not the Rotec. It has a float bowl so doesn't suffer from burping. What you are intending to do is very similar to what I have, One electric backup and one mechanical pump. This may or may not be some help.
I have an electric facet pump on the cockpit side then through the firewall to Gascolator, to mechanical fuel pump, to Bing carburetor. The 2 pumps are in series. I use only the mechanical pump 100% of the time. The electric facet pump is my only backup. It will pump through the mechanical pump and the mechanical pump will suck through the electric.
The mechanical pump is also a restriction to flow. Looking at your schematic I would not expect to see a usable fuel flow with gravity feeding unless you also add check valves in parallel with both pumps.
Here is my fuel schematic
Steve
Sonex 892

[lpaaruule]

Just got the electric fuel pump wired up. Here is a short video of my vapor return line in action.

http://youtu.be/T36-qAfTW_o

As you can see, even with a 1/32" restrictor orifice, there is still quite a bit of flow.

I performed a preliminary fuel flow test with the electric pump running, and still got 15.7 gal/hr at the TBI even though a good amount of fuel was going to the vapor recovery line. During the last gallon of the test I realized that the primer button wasn't in all the way, so next fuel flow test I expect more.

I think I might make the vapor return orifice a little smaller. Perhaps around 1/48".

[WaiexN143NM]

Hi all, paul,
What mfgr. And model electric pump are you using? We had a facet pump, i'll have to look up the model number. Great to hear your model has little restriction. We are open to modifing our system if something looks better/safer. Weve never run our tank low because of cg concern. May be safer with a pump , with lower gravity head pressure when running the fuel tank level lower.

Thanks paul,

WaiexN143NM
Michael