Return line

Paul Austin · #1 10-26-2008, 05:34 PM

Hi just a quick question about return line on fuel injected engines do all fuel injected engings need a return or is it just some particular setups and if so can it be plummed back into the supply line before all the valves and pumps.

Chappyd · #2 10-26-2008, 06:23 PM

I'm pretty sure it is particular set-ups. I know one for sure, I think ECI's system does require a return line. My set up does not. I'm using the experimental from Vans, IO 360 M1B, with I think it's a silverhawk? Sorry to be fuzzy on the details, but it's been a while since I looked at it

I do recall looking into it at the time I was researching different options. I beleive my set up will require a "hot start routine" that may have been different had I put a return line in. I'm using Van's stuff and plans. I may experiment on my next experimental

There is some good reading in here if you get the right search term.

Try fuel injection set up

flion · #3 10-26-2008, 07:19 PM

And to the left, Airflow Performance's setup does not require a return. So, it depends on the system. If you haven't built your tanks yet but are angling for a FI system, I'd plumb for the return so you have some flexibility. In my case, FI was a last-minute thing, so I was glad not to have to go back and do a return.

David-aviator · #4 10-26-2008, 07:33 PM

Quote:

Originally Posted by Paul Austin

Hi just a quick question about return line on fuel injected engines do all fuel injected engings need a return or is it just some particular setups and if so can it be plummed back into the supply line before all the valves and pumps.

With Airflow Performance a bypass is needed to regulate fuel pressure at the electric pump. The mechanical pump on the engine needs no bypass. The pumps I have are capable of 100+ psi so pressure regulation is a required part of the system. This is accomplished with a valve that opens at whatever pressure it is rated. The AFP system requires 25 psi. I believe electric fuel pumps in general aviation need a pressure regulating bypass (except the low pressure Facet pump, it runs at 6 psi).

With my set up, the bypass fuel goes back to the supply tank via the 6 port Andair valve. An optional method with the standard 3 port valve is to set up a "loop" whereby the bypassed fuel is plumbed to the inlet fuel line and immediately returns to the pump. This works fine with many installations but has a down side in that this circulating fuel can heat up. If the electric pump is used only for take off and landing this may not be a big deal but it does leave one with unpressurized fuel to the engine driven mechanical pump forward of the firewall in a very warm environment when the electric pump is off. Unpressurized fuel will vapor lock much sooner than if it were under pressure. For this reason I have decided to run an electric pump continuously as with the Subby installation and in fact have elected to keep both pumps as installed. The only change to make this work is a bypass around the pumps with a check valve to provide for gravity feed to the engine pump should electric fail. Injection electric fuel pumps generally do not provide for flow through when off.

This is off topic, but there is a neat feature with AFP - the purge valve at the spider divider. This mechanical valve relieves pressure in the system after shutdown and returns any residual hot fuel to the supplying tank or the incoming line at the valve. This valve should do away with any hot start issues in that fresh relatively cool fuel will be available any time for start.

David-aviator · #5 10-26-2008, 07:38 PM

Quote:

Originally Posted by flion

And to the left, Airflow Performance's setup does not require a return. So, it depends on the system. If you haven't built your tanks yet but are angling for a FI system, I'd plumb for the return so you have some flexibility. In my case, FI was a last-minute thing, so I was glad not to have to go back and do a return.

Patrick, if you check the plumbing of your system you will find the bypass valve is plumbed back to the inlet line. There is no other way to regulate the pressure.

Walt · #6 10-26-2008, 08:03 PM

Bendix does not need a return; AFP should have one which is used with the purge valve and needs 1 line back to either tank; ECI must have a return and the 2 port Andair valve to return unused fuel back to the same tank being used from.

flion · #7 10-26-2008, 08:50 PM

Quote:

Originally Posted by David-aviator

Patrick, if you check the plumbing of your system you will find the bypass valve is plumbed back to the inlet line. There is no other way to regulate the pressure.

Yes, but that is not the same as a return to the tank, which is what I felt was being asked. Van's FWF for FI has the bypass plumbed back to just downstream the selector, as you mentioned - no need for a return to the tank.

By the way, my AFP manual suggests just dumping the purge over the side. I haven't actually needed to use the purge for a hot start yet, but I expect that the loss would be minimal if you are quick on the valve when the engine starts. That's not the voice of experience speaking; I'm trusting AFP on this.

Don at Airflow · #8 11-04-2008, 05:18 PM

By the way, my AFP manual suggests just dumping the purge over the side. I haven't actually needed to use the purge for a hot start yet, but I expect that the loss would be minimal if you are quick on the valve when the engine starts. That's not the voice of experience speaking; I'm trusting AFP on this.[/quote]

Wasn?t here last week so I am getting caught up on e-mails and such, but there?s some incorrect information here. Airflow Performance DOES NOT recommend dumping the purge return overboard. READ THE MANUAL. We recommend teeing the purge return to one of the tank feed lines. You can run the purge return to a tank but it?s not necessary. The boost pump does not require a return to the tank either. In fact we don?t recommend it as the fuel system has to be sized to flow 37 GPH on the suction side of the boost pump. Simply tee the boost pump relief valve to the inlet of the boost pump feed line. Also a simple selector valve (left, right, off) is all that is required for an Airflow Performance fuel injection system. You don?t need an expensive 6-port valve (we get that question a lot).

Don

flion · #9 11-05-2008, 04:11 PM

I stand corrected. I checked my manual (not that I doubted Don, who has been very helpful with my questions in the past) and didn't find that anywhere. I wonder where I got the notion from? Anyway, I will be plumbing a return. (I have to say, though, that I haven't used the purge valve much and, in the couple of hot starts I have done, very little fuel was lost as I closed the valve once the engine fired. I lose more fuel checking the tanks for water.)