Stuck non return valve in electric fuel pump

HI All,

I just wanted to report on a recent experience in my RV-10.

I built an RV-10 about 2 years ago and have the standard Vans electric fuel pump. I also have a return line going to both tanks through an Andair duplex selector via a fuel pressure regulator (FPR). The FPR allows me to dial in my fuel pressure exactly to what I want irrespective of usage / RPM / climbing etc, so my fuel pressure after the mechanical fuel pump to the injector is always constant, and the flow in my return line is variable and optimised for max cooling of the mechanical fuel pump. I run 98 RON ethanol free mogas that is always fresh and filtered through a Mr Fuel filter, and I have had no problems with water or debris in the fuel. I run the boost pump on TO / Landing and to prime, and have never had any signs of vapour lock.

About a week ago, I made a trip to a remote desert to drop some kit off to a friend who works in a remote safari camp. The strip there was very rough and short and the air and ground were so hot that putting the girl down was difficult. After a go around, I finally got her down and by now she was hot. Oil temp was 245 and CHT's were in the 400-410 range. After parking up I shut down and left the fuel selector on left tank (I normally switch it off).

After about 2 hours, I came back to the airplane and my normal hot starting procedure of fullest tank selected, primed with the electric pump for a few secs only and then crank while enriching mixture till she fires and runs, didn't work. The engine coughed but didn't run. Tried again, no good, after another 2 tries, with headset off now, I noticed that the priming sound wasn't right, the electric pump was running, but I couldn't hear the normal gurgling of the fuel and the fuel pressure with the pump running didn't go over 5-7 PSI.

Now I knew I had a problem and got into a panic! With over 200 miles and 8 hours of drive through bush country to the nearest town and no car around, getting help wasn't going to be easy, and I had only the very basic of tool kits with me (I normally have a bigger toolkit but I left it at base on the day). Still I decided to systematically try and diagnose and fix the issue. I had fuel in the tanks. I checked the filters, they were new and had no debris in them. removed the fuel lines to and from the mechanical fuel pump and found with the electric pump running, there was only a trickle of fuel coming out. I blew through the return lines and they were clear. With the centre console off, the pump was running and humming away on touch, but not drawing fuel through the filters. I then removed all the fuel line connections and removed the fuel pump thinking there must be some debris stuck in it. pump was completely clear and when run bare, generated plenty of suction as normal against my finger. Then the problem struck me... The non return valve that runs parallel to the fuel pump was stuck midway, and I could blow through the valve both ways. When disassembled, the plastic ball was stuck in the cage midway with no evidence of debris or any restriction. Once washed in a little bit of fuel and reassembled, it started working again normally.

I presume that the plastic ball in cage return valve allows you to prime and pressurise with the electric fuel pump (when closed) and then opens to allow the mechanical fuel pump to draw a column of fuel from the tank while bypassing the electric fuel pump. Stuck midway, the electric pump couldn't prime and build pressure and the mechanical pump couldn't maintain an air free column of fuel in the line to support a running engine.

Everything reassembled, fuel pressure shot up to 35 PSI with the electric pump on and the engine started first time. I took off and made it back home with no issues, and have since flown another 10 hours with no problems.

Anyone had an experience like this before? I personally think that in my case, that leaving the fuel selector on a tank rather than OFF on shutdown allowed vapour pressure generated in the fuel lines from a hot engine to back pressure and push the ball in the return line and stick it midway.

I learnt 3 things from this experience: Switch your fuel selector to OFF once you park up, especially when the engine is hot. Always carry a comprehensive enough toolkit with you when you fly to open up and check most things. Don't panic if you get stuck, be systematic and work through things.

Any comments welcome.

Safe flying and happy landings all

Best Amer

Those pump assemblies are pretty reliable. I suspect that having two pressure regulators inline allowed the std pump's regulator to spend most of it's time in the middle position or something different than what is seen in std installations that do not have a second regulator installed. Or, after shut down, your downstream FPR is holding pressure on the std pump, not allowing the ball to move to it's normal resting position.

In the newer models, the bypass and pressure regulator function are built into the same valve. Suggest you contact Don at AFP to discuss the installation of a second FPR unit and how this relates to your installation. I doubt it was a one time occurence and should expect to see it again. You have added backpressure to an otherwise integrated system, so not surprised that it is not functioning as designed.

Larry

Impressed that you were able to smartly troubleshoot the problem in the field. Many would have been struck. Impressive job.

What is the boiling point of the fuel you are using. How is it effected by these extreme temperature conditions and may it have caused the start of your fuel event?

Vans sells Air Flow Performance fuel pumps which, I believe, use a gate valve. Not a ball check valve. If they now use a ball valve call them. They are a wealth of knowledge and may have some ideas. Does this ball just float in the fitting or is there a spring to lightly seat it. What is the ball made of. The fuel type may have effected it.

George Meketa

Thanks for your comments guys

My installation of a second FPR in the return line was prompted by some episodes of what seemed to be lean running on take off when first test flying. Previously I had an AN fitting going to the return line and a machined restrictor with a hole in it. I found that as the hole got smaller, through testing, the engine ran better on take off and high power, fuel pressure values became more stable, but I was worried about the possibility of vapour lock on approach and landing with such a small amount of return fuel cooling the fuel pump and lines through that tiny pin hole.

So I thought to myself "fuel usage is a dynamic process, you use more on take off and less in cruise, so the return should be dynamic and allow less cooling fuel through when needed for the engine on take off and more on landing and approach when power is reduced". The obvious solution to me was to put a FPR in the return system. Now the return would be variable depending on the engine usage, while still maintaining stable optimum fuel pressure at all times. Once fitted, all my engine fuel problems and worries went away, until now it seems...

I think because I left the fuel on a tank that vapour pressure in the return line may have pushed the ball back, but then without a return line, wouldn't that happen as well? In any case, I have been back to that desert twice since. Landed in the same heat with everything super hot and this time put the fuel selector to OFF and on return a few hours later, very fortunately, everything was ok and starting was easy.

I wish I had taken photos. I cannot remember seeing a spring in the check valve system. I can just remember a cylindrical cage and a plastic white ball loose in the cage. Perhaps there has been an upgrade to swing style valve rather than a ball. I emailed Don about it but he hasn't got back to me yet.

I confess that I would be reluctant to change the system that has worked for me thus far, apart from this little hiccup. Where I fly it can be super hot and air temps can be as hot as 40 degrees on the ground, when taking off from short dirt strips and at 6,000 ft AMSL in those temps, things get hot very fast and vapour lock is a real danger. Getting Avgas can be hard and the cost is 4x what my unleaded fuel costs me now. I haven't checked the boiling point of the petrol I am using, I will ask the fuel company and see what they say.

Thanks again for your comments

Safe flying and happy landings all

Best

Amer

amerkarim said:

I found that as the hole got smaller, through testing, the engine ran better on take off and high power, fuel pressure values became more stable, but I was worried about the possibility of vapour lock on approach and landing with such a small amount of return fuel cooling the fuel pump and lines through that tiny pin hole.

Click to expand...

Don't know what FI you have, but the bendix unit provides a very stable fuel delivery from around 12 PSI up to about 50-60 PSI of fuel pressure. I would be somewhat concerned that you have restricted flow to the servo with the side affect being better running engine due to leaning. On my 320 with FP prop, I have to pull the red knob out about 1/2" - 1" on T/O's at 800 MSL otherwise I lose some power due to being overly rich. I suspect the servo is set up to deliver the fuel needs of a CS prop-based engine, which would be much higher at T/O. I usually have to richen the mixture a bit as I level off my climb and the RPMs go up. I use EGT to determine the fuel need.

If in fact, you are artificially reducing flow in the servo with your second FPR, that could set up other issues down the road. Much better to lean via the red knob when necessary. Hopefully Don will give you some insight/guidance.

I remember that Don did some testing and ran his pump at very low flow rates (i.e. most fuel was reciculating in the pump) and he found that temps did not become objectionable for over 45 minutes. I don't believe that a separate recirculation path is required at the pump. I have a separate recirculation path from the servo to the tank, with a discrete valve, to help deal with hot fuel from heat soak. I find this a requirement with mogas and high ambient temps after a fuel stop.

Larry

Hi Larry

I have an airflow FI, working range is 18 to 45 PSI I think.

My FPR is fitted after the engine mechanical fuel pump. There is a 4 way tee that comes off the pump. 1 arm comes from the mechanical pump, 1 goes to the FI, one to the fuel pressure sender and the last to the return line via the FPR. The FPR now allows you to dial in what pressure you want in the line supplying the FI. I have set my pressure to 25 PSI, so all flow above 25 PSI goes into the return line taking heat with it. Now my fuel pressure is constant in all stages of flight, TO, cruise, approach, taxi, irrespectice if the boost pump is on or not. In fact putting the boost pump on just trebles my return line flow as my pressure will always be what I have dialed it in to (25 PSI). This system makes hot starts easy as well as you just turn the boost on without touching mixture and it washes the whole system cool with fresh fuel and returns it to the tanks.

My worry is not the heating of the fuel and vapour lock in the electric pump, but in or after the mechanical pump, in the line to the FI.

I have a similar setup to yours, its just that yours has a manually operated valve for purging hot soaked fuel to the tanks on hot days and for hot starts. Mine is a similar return system to the tanks, but mine is working all the time, it has a variable flow rate that is inversely proportional to the engine's fuel consumption.... when the engine uses more fuel for climbing or TO, power is more, the return flow is automatically reduced to maintain the dialied in pressure (25 PSI) and the mechancal fuel pump gets a bit hotter.... When I am in cruise or approach, power is less, the engine is using less fuel and everything is much cooler due to the automatically increased return flow of fuel to the tanks, carrying the heat away with it. This system in my mind will reduce my chances of getting vapour lock because the optimum amount of fuel is always circulating the returning to the tanks carrying away the heat that causes vapour lock.

My comments about leaning during my testing phase were because originally I had a fixed orifice in my return line and I think I made it too big. on TO, I was now starving the FI so I was running lean and things were getting hot and rough.

I am much happier with my new system now. So far, it seems to have solved my problems. My fuel pressure is always 25 PSI and my mechcnical pump must be cooler with optimised return flow. If you are running mogas then I recommend thinking about installing an FPR into a retun line yourself.

Best

Amer

A few questions:
Have you verified that at full throttle, full rich, you?re getting about 24 g/hr fuel flow to the engine?
I am guessing that your 98 RON gas is about 94 pump (R+M/2) octane, and about 90 Motor octane? If you?re running the Lycoming IO540D4A5, you know that this is less than the minimum Lycoming spec?
What octane additives are in this fuel? Any chance they may be attacking the plastic ball valve?

Hi Bob,

Yes my fuel flow on full power full rich is about 24 GPH.

The mogas I am using is 93 AKI ethanol free. I get it fresh from a trusted gas station and filter it before putting it in the plane. I have never had an episode of bad fuel from there and the engine runs smooth and cool with it. No pinking, strange noises, or evidence of detonation. I run ROP always, and have no interest in trying to run LOP with the fuel price as it is, and the extra speed I get ROP. Also I am then safely out of the danger zone for detonation.

I use aeroshell AD oil 100 or 120 depending on what I can get, with camguard, and change the oil every 25 hours. I have 1 standard mag and 1 Electroaire ignition system. My mag drops are well within limits. On a tarmac runway with no flaps at sea level, 2 on board, full fuel and no wind, I get airborne in about 12 seconds. My cruise is about 155 to 160 KTS WOT, but then I have big bush tyres for the rough strips that I go into, and no wheel pants.

I don't know what additives the fuel has in it, but I just know my engine likes it. I have tried other types of mogas and the engine wasn't as smooth. I have also used 100ll and there wasn't much difference between that and this fuel I am using now. 100ll was just very hard to get where I am, and 4x the price.

The plastic ball was perfectly smooth, glossy and shiny. There was no evidence that the fuel was doing anything to it.

Best

Amer