Fuel pressure regulator on return line setup

Hi All,

Just making an enquiry if any of you have used an adjustable fuel pressure regulator on your return line setup.

I have put in a return line on my RV-10 using the Andair duplex valve in the hope to run some mogas in the future. I am having fluctuating pressures during my test flying. Sometimes I think I have opened the return line valve too much and sometimes not enough as the fuel pressure is up and down. When I switch on the electric pump the pressure surges and I am not happy about it being very high, as it puts a strain on the pipes and fittings and encourages a leak.

I was thinking of installing an adjustable fuel pressure regulator and tuning it to about 20 PSI, that way the fuel pressure after the mechanical pump supplied to the injectors, is at a constant pressure all the time, and everything else can go in to flow back in the return line to the tank, taking some heat away from the fuel pump as it goes. When you then engage the electric pump you would get a lot more flow and the same pressure that you had dialled in before of 20 PSI.

Any comments, suggestions, advice ... etc

Thanks

Amer

I will offer a very simple answer....

Be very careful when designing / modifying the fuel system for an aircraft.


Fuel system issues is one of the highest causes of engine stoppage in experimental aircraft.

I suggest you ask your self a few questions. Start with "Are you making a design change that is fixing something that has proven it self to be a problem?"

+1

What he said^^^^^

amerkarim said:

Hi All,

Just making an enquiry if any of you have used an adjustable fuel pressure regulator on your return line setup.

I have put in a return line on my RV-10 using the Andair duplex valve in the hope to run some mogas in the future. I am having fluctuating pressures during my test flying. Sometimes I think I have opened the return line valve too much and sometimes not enough as the fuel pressure is up and down. When I switch on the electric pump the pressure surges and I am not happy about it being very high, as it puts a strain on the pipes and fittings and encourages a leak.

I was thinking of installing an adjustable fuel pressure regulator and tuning it to about 20 PSI, that way the fuel pressure after the mechanical pump supplied to the injectors, is at a constant pressure all the time, and everything else can go in to flow back in the return line to the tank, taking some heat away from the fuel pump as it goes. When you then engage the electric pump you would get a lot more flow and the same pressure that you had dialled in before of 20 PSI.

Any comments, suggestions, advice ... etc

Thanks

Amer

Click to expand...

So for what it?s worth, I?ll add my 2 cents. If you have an EFI/EFII, high pressure, continuous fuel flowing system, you?ll need a fuel pressure regulator, but with a standard aircraft type of fuel injection system where you typically wouldn?t incorporate a return line, then I?d say a fuel pressure regulator isn?t called for. I think a very small metered (1/8?) fuel return line is all you need.

Correct me if I?m wrong but I?m assuming that the main thing you?re trying to accomplish is to have the ability to flush out any hot fuel and vapors that could cause hot-starts or vapor lock? If so, I think a simpler way to design your fuel return system would be to incorporate a small 1/8? metered return line to just one of of your tanks. You could control it with either a manual on/off valve or an electric on/off solenoid valve/switch. I actually think a solenoid valve would be the cleanest/simplest way to do it.

Designing this way you accomplish what your wanting it to do, which is to get rid of that hot fuel and vapors and you?ll have the safety aspect of a very simple setup that that won?t affect the fuel pressures and required fuel delivery to the engine....even if you were to forget to close off the fuel return line valve.

My buddy actually has a setup like this on his -7 and it works like a charm. He was having really bad vapor lock issue but when he designed in this simple return line setup, all of his vapor lock and hot start issues went away.

Mark

I agree with Scott----I'd certainly check with the manufacturer of the system and see what their recommendations are for fuel pressure. The SDS and EFII systems have regulators in the return sides.

Tom

I'll add that the EFII fuel pressure regulator also utilizes manifold pressure to adjust pressure slighly with their regulator.

Regulator system detail

HI All,

Many thanks for your replies, many points taken and understood. But isn't vapour lock and or hot starting common and potential serious problems? Please allow me to expand a bit on my system and suggestions:

I have the standard stock fuel system, not EFI or anything special.

I already installed a return line. it is an AN6 teflon and stainless braided line. I have a tee that comes off the mechanical fuel pump. One arm off the tee goes to the engine and pressure gauge. The other goes to an adjustable valve or stopcock, and then to the return line. This goes via the Andair duplex valve back to the tank that the feed is coming from.

I have been experimenting with the adjustable valve or stopcock. When I open it, I get more flow going back to the return line, that is good for temps and the fuel pump is noticeably cooler reducing my chance of vapour lock and making my hot starts easier, but my fuel pressure drops. When I close it, I get less return and the pump is hotter but fuel pressure is higher etc etc.

The question is how much to open this stopcock ??? Too much and the pressure is low, too little and the pressure is high and the pump is hot.

"Put it in the middle stupid !!!" Yes I hear you, but ...

I have also noticed that during flight the fuel pressure fluctuates normally, and when I put the electric boost pump on, when coming in to land, or when slowing down and when I think I might get vapour lock, or when clearing hot fuel out of the system for a hot restart, the pressure surges and becomes very high, presumably because of the restriction in the stopcock / return valve and now 2 pumps are running, not just one. This can be alarming to me, as I don't want a pipe to burst or start to leak or to generate very turbulent flow. In my experience, when things change rapidly you can develop a problem.

I want a fuel system that gives me a steady constant fuel pressure, whichever pump I run (mechanical, electrical or both together) while maximising return so the mechanical and electrical fuel pump are kept cool with plenty of fresh fuel passing through them.

There are compact and very light aluminium adjustable fuel pressure regulators that are used in racing cars, that have 4 connections: AN6 Input, AN6 return to tank, AN6 fuel to engine, and an atmospheric port AN4 (to compensate for altitude). They have an adjustment dial that allows you to dial in any fuel pressure from 10 PSI to 100 PSI in ? PSI increments.

When fitted, despite fluctuations in the pump pressure (mechanical or electrical), the fuel pressure output to the engine will be regulated to a constant value that you can pre set. All the rest of the fuel flow will now go into the return line without turbulence, maximising the return flow and keeping everything cool. The atmospheric port will maintain the fuel pressure you have set relative to the outside air pressure so that fuel pressure is constant and what you pre set at any altitude.

The regulator is aluminium, has a bracket to mount on the firewall and comes with its own teflon stainless braided hoses. The materials within the regulator are ethanol, methanol etc safe so it should be fine to use with mogas or avgas.

Has anyone tried using these, or what are your thoughts on the idea of fitting one?

Thanks in advance, sorry for the long message.

Amer

Amer,

I strongly recommend you not do this.

Add a simple purge valve if you have a hot start problem (I never did with the IO-540). If you really must have a fuel return line that is always flowing gas, make it out of 1/8? stainless or such to limit flow to about 1gph. This was the ?if everything else fails? vapor lock solution for Ellison throttle body injection systems.

Carl

Amer,

I understand that you?re not only trying to avoid vapor lock, but you?re also worried about the health of your fuel pumps along with being concerned about your fluctuating fuel pressures.

Regarding the fluctuating fuel pressure, I won?t really comment on that. Without seeing it first hand I?d really just be guessing. However, the fuel return line subject is a little more straight forward. Like myself and others have suggested, keep it simple and use a small 1/8? return line to purge the hot fuel and vapors back to your tanks.

Think about it this way: With your setup you really don?t need to actually control fuel pressures as would be required with an EFI/EFII configuration.....your system is already designed to handle that. The EFI/EFII systems require a constant fuel pressure (45-50 psi) in the fuel rail because that?s what the electronic solenoid injectors need to operate properly. Once again, you don?t need this.

In your case, you only need something in place to purge out that hot fuel and vapors, and that?s where the small 1/8? purge line comes in. Basically, you want something that?s simple and if you were to forget it open it wouldn?t affect the required fuel needed to keep your engine running.

The fuel pressure regulators that?s used with any high pressure systems like an EFI/EFII requires that a vacuum line coming from the intake manifold be connected to the regulator so that MAP can be measured. This allows the fuel pressure regulator to keep the rail pressures constant as the vacuum pressures fluctuate. Once again, you don?t need all of this fancy stuff. All you need is that simple little 1/8? return line that?ll allow you to purge out those hot vapors and actually allow your system to work as it?s designed to.

Like I?d mentioned before, I think an electric, in-line, solenoid valve would be the way to go. I?d have it wired to a three position toggle switch...(OFF/Electric fuel pump on/Electric fuel pump on and purge valve open). I?ll let the experts advise you on weather to get something that?s turn key or how to design your on....heck, I?m just a shade-tree mechanic so take everything I say with a grain....(uhhhh ?a box?) of salt!!

Mark

What is the mode of this regulator when the feed line pressure is LESS than its preset minimum? It could be that fuel pressure in the feed line is what controls the position of the regulator. In this case it seems like you would have an open line back to the tank through which your engine driven pump might try to suck air. This seems like the bad thing others are aluding to.

If the regulator valve is sprung fully closed until line pressure exceeds the set point then maybe this won?t happen. Keep in mind that with the engine pump ?sucking? pressure in the feed line upstream of that pump will be less than ambient, so that also might affect the position of the regulating valve.

Just my thoughts to help you understand the problems that these other arguably more knowledgeable responders might be concerned about.

Sorry for appearing dramatic, but I find this thread to be truly SCARY!

I too am in league with earlier posters who advise to "DON'T DO IT." But I will go a bit further to suggest what you should do.
You should contact the fuel injector manufacturer technical support and describe what you are experiencing (or trying to prevent experiencing), describe your non-standard fuel plumbing set-up, and follow their suggestions. Also talk through what is, and how to prevent 'vapor lock' with them.
I did a quick web search and found that at least one manufacturer offers a purge valve set-up that mounts on top of the engine to clear vapor lock from the fuel spyder, you might institute this type of solution for hot starts.
In the mean time, if you go flying CLOSE THAT VALVE!

As Scott said:
"Be very careful when designing / modifying the fuel system for an aircraft.

Fuel system issues is one of the highest causes of engine stoppage in experimental aircraft.

Thanks All,

Makes more sense to me now.

Where I fly it is hard to get decent avgas and it is very expensive when you get it, so a lot of flying will be with mogas that is easily available and cheap (Shell V Power 98 RON), outside air temps can also get to 40 degrees centigrade, hence my apprehension about vapour lock and installing a return line to start with.

I like Mark's suggestion of a reducer sitting in my AN6 return line with a 1/8" orifice to allow just enough flow to get bubbles and vapour out. I also have a non return valve that I will fit just before the return line plumbing to stop air coming back the other way. Let me have a go and see what happens.

Many thanks again and happy landings

Best

Amer