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Fuel pressure problems

Phantom30

Well Known Member
Guys..I need help trying to understand Van?s RV-12 fuel flow system. In looking at the plans 46...specifically the multiple bango fitting thingy where the fuel supply from the engine driven pump feeds, the supply for both carbs branch off...then the upper w/flow metering jet controls flow return to the fuel tank.

My question is....is the fuel pressure sensor take-off before or after the flow restrictor? By looking at the figure drawing...the restritor is installed controlling flow to both return and pressure sensor.

Scott..help (i?m Chasing grimlins)
 
Hi Ric - the line of the fuel pressure sensor, the return and the two carbs all come of the fuel distribution block. The restrictor is in the return line hose and only restricts return fuel back to the tank.

I'm Mark Winslows friend and he has my contact details, so please call if I can help you in any way.

Julian
 
Guys..I need help trying to understand Van’s RV-12 fuel flow system. In looking at the plans 46...specifically the multiple bango fitting thingy where the fuel supply from the engine driven pump feeds, the supply for both carbs branch off...then the upper w/flow metering jet controls flow return to the fuel tank.

My question is....is the fuel pressure sensor take-off before or after the flow restrictor? By looking at the figure drawing...the restritor is installed controlling flow to both return and pressure sensor.

Scott..help (i’m Chasing grimlins)

If everything is assembled correctly the fuel that feeds both carbs and the pressure sensor is before/upstream of the restrictor.

The restrictor is inside of the double banjo fitting on the top of the block.
The actual restrictor is inside the hose barb leg that the return hose going to the firewall fitting is connected too. If this hose assemble is installed backwards (so that the restrictor is on the pressure sensor leg) the system pressure will be very low because there is an unrestricted flow path via the return line back to the tank.

I don't remember the details (and don't have plans at home) but I think there might be a restrictor that is supposed to be removed from the bore of the banjo bolt when the double banjo fitting is added to the top.

Edit - Found it Page 46-09 at this link http://www.vansaircraft.com/pdf/revisions/RV-12/RV-12_46.pdf
Page 46-07 is where it instructs the builder to remove the pilot jet (restrictor).
 
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NOT wanting to open the flame war again--

but the restrictor in the double banjo was one of the reasons Steve and I came up with our teflon hose package. Yes, with 2 hoses that were fairly close in length, we found some builders were installing it backwards--yep with some effort since one of the hoses is shorter. So we made an attempt to eliminate that possibility.
On the same note-- the other reason we looked into this was the RTV sealing of the hose and firesleeve area at the banjo. We found several builders were PULLING the firesleeve out of the bands, AND pulling the hose (rubber at that time) off the banjo stems. This was tearing the liner of the hose, since the barbs are designed to lock the hose in place. Some builders were sealing the ends and pushing the hose back on the barbs with a damaged end of the hose. Some even had some fuel leaks after reclamping due to the torn hose liners.
That was the big reason we designed our kit package- to try to eliminate the possibility of damaging the hose. GRANTED----there were many builders that had no issues at all, and everything was fine---we have one at 3J1. It was the others that we made our teflon hose package for.

Tom
 
but the restrictor in the double banjo was one of the reasons Steve and I came up with our teflon hose package. Yes, with 2 hoses that were fairly close in length, we found some builders were installing it backwards--yep with some effort since one of the hoses is shorter. So we made an attempt to eliminate that possibility.
On the same note-- the other reason we looked into this was the RTV sealing of the hose and firesleeve area at the banjo. We found several builders were PULLING the firesleeve out of the bands, AND pulling the hose (rubber at that time) off the banjo stems. This was tearing the liner of the hose, since the barbs are designed to lock the hose in place. Some builders were sealing the ends and pushing the hose back on the barbs with a damaged end of the hose. Some even had some fuel leaks after reclamping due to the torn hose liners.
That was the big reason we designed our kit package- to try to eliminate the possibility of damaging the hose. GRANTED----there were many builders that had no issues at all, and everything was fine---we have one at 3J1. It was the others that we made our teflon hose package for.

Tom

I am not clear on why a more expensive hose is justification to prevent someone from installing a hose incorrectly, when the instructions are very clear about saying "use caution, this hose can be installed backwards", and then goes on to explain in clear detail how to double check that it is correct.

As for the RVT reason....
This hose assembly was redesigned many years ago (eliminating the RTV sealing process and any tendency for the hose to separate) so that hasn't even been an issue for a long time.
 
Scott--

"I am not clear on why a more expensive hose is justification to prevent someone from installing a hose incorrectly, when the instructions are very clear about saying "use caution, this hose can be installed backwards", and then goes on to explain in clear detail how to double check that it is correct.

As for the RVT reason....
This hose assembly was redesigned many years ago (eliminating the RTV sealing process and any tendency for the hose to separate) so that hasn't even been an issue for a long time."

We didnt do it to keep someone from installing the hose backwards, even though YES is was clearly labeled, but guys were doing it anyway. Big reason was to use a teflon hose to eliminate the rubber hose liner deterioration that was happening at the time with the fuel additives. Guess thats why Rotax went to teflon for the carb hoses, and I assume thats what the new Rotax fuel hose assembly is. Is the VA216 assembly now rubber or teflon? And is the gascolator to fuel pump hose still rubber, or is it now teflon?

YES the RTV thing was many years ago---circa 2011, and YES it has been rectified.

Again----not wanting to get into a flame war here.

Tom
 
We didnt do it to keep someone from installing the hose backwards, even though YES is was clearly labeled, but guys were doing it anyway.

Ok, but it seemed like that is what you said.....

but the restrictor in the double banjo was one of the reasons Steve and I came up with our teflon hose package. Yes, with 2 hoses that were fairly close in length, we found some builders were installing it backwards--yep with some effort since one of the hoses is shorter. So we made an attempt to eliminate that possibility.




I believe the updated version VA-216 is teflon.

The gascolator to engine driven fuel pump hose is part of the engine as supplied by Rotax. The current version is teflon
 
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If everything is assembled correctly the fuel that feeds both carbs and the pressure sensor is before/upstream of the restrictor.

The restrictor is inside of the double banjo fitting on the top of the block.
The actual restrictor is inside the hose barb leg that the return hose going to the firewall fitting is connected too. If this hose assemble is installed backwards (so that the restrictor is on the pressure sensor leg) the system pressure will be very low because there is an unrestricted flow path via the return line back to the tank.

I don't remember the details (and don't have plans at home) but I think there might be a restrictor that is supposed to be removed from the bore of the banjo bolt when the double banjo fitting is added to the top.

Edit - Found it Page 46-09 at this link http://www.vansaircraft.com/pdf/revisions/RV-12/RV-12_46.pdf
Page 46-07 is where it instructs the builder to remove the pilot jet (restrictor).

Thanks Scott...couldn?t figure where the restrictor was located...

Now, too add a mechincal pressure port for 0-10 psi gauge too verify sensor reading...but starting to suspect ?crap? is pugging the bango fittings.
 
Ric---install a temporary TEE just before the pressure sender. That way you can read both pressures at the same time.

Why do you suspect '****' plugging the banjos? Are you seeing bits of black residue in the hoses?
Be sure to let us know!
Tom
 
Ric---install a temporary TEE just before the pressure sender. That way you can read both pressures at the same time.

Why do you suspect '****' plugging the banjos? Are you seeing bits of black residue in the hoses?
Be sure to let us know!
Tom

Now, really stumped. Put a mechanical gauge in place of psi sensor. Flow tested (using aux pump) at feed to new mechanical pump (got 1/2 gal in 90 seconds) which equals 20gal/hour....should be plenty🙄

Pulled bango fittings top/bottom to check for pluggage....none. Ran engine..got same results @ 5200 rpm sucked pressure down to less than 1 psi.

Pulled fuel tank return line loose @ fire wall...plugged to stop flow...restart engine...same results. I?m stumped....help?
 
I may have misunderstood your last post. Was the drop in pressure present on the mechanical gage too? Have you tried disconnecting all the hoses and blowing them out with air? Any chance the red cube is plugged?
 
Electrical fuel pressure sensors are notoriously inaccurate. Mechanical gauges can not be trusted either unless their accuracy has been verified. To check the accuracy of the mechanical gauge, remove it from the airplane and attach clear plastic tubing about 10 feet long. Fill the tubing with water so that the water level is 83.2 inches above the gauge input port. The gauge should read exactly 3 psi.
 
Rich;
"Put a mechanical gauge in place of psi sensor".
I'm seeing that Ric put the gauge in place of the sender, and not in conjuction with it. Was showing the same 1psi result as what his Dynon was showing. SURE---having the gauge plumbed with a tee just before the sender would allow you to read BOTH the mechanical gauge and the Dynon from the same source to compare the readings. My FLAWED LOGIC says that if they are different with the gauge being higher and possibly more correct, then a faulty sender is a good candidate.
If they read the same, then check the hose and the source location.
If necessary, check it at the pump discharge port to verify the pressures.
IF the pressure is 'normal' at the pump, then there is some sort of anomaly between the pump, through the system to the gauge/sender location where you originally take the pressure readings. If the pump pressure is also low, then check the supply from the gascolator to the pump.
It is NOT beyond the realm of possibility that the supply hoses 'could' be partially collapsing under the suction of the pump, IF they are the rubber hose, and IF the pumps suction is sufficient enough to develop enough force to partially collapse the hose.

Ric didnt say whether or not his test was WITH the boost pump running or not. Since the plans call for the pump to be running all the time, I would assume his test was with the boost pump on. So--again FLAWED LOGIC, you would think that IF the boost pump were producing proper discharge pressure, then the fuel pressure supplied to the mechanical pump would be 2.5-5 psi ( or whatever it is). IF it is NOT ( as measured at the supply port of the mechanical pump) then obviously there is an issue with the supply system. Tank, tank vent, cabin lines, boost pump, flow transducer, gascolator, supply hose. Easiest test would be to open the fuel cap and create a large vent. Rerun the test and see if anything changes. IF everything operates normally, then FLAWED LOGIC would tell me to look at the vent system, and repair/update as necessary and retest.
IF the vent test yielded the same low pressure results, then there is something in the supply side.

IF the measured pressure was with the boost pump OFF----then recheck it with pump ON and see if the pressure rises. IF it doesnt, then check the boost pump pressure. Just because it may be running, doesnt mean it's producing the necessary pressure.

By systematically point by point testing and restesting you will find the problem. YES its time consuming but much less expensive than guessing and throwing a bunch of parts at this and seeing if that fixes the problem. Doing so may in fact 'fix' the problem for a while, but if you havent found the actual culprit, then it will occur again.

OH----I mentioned the rubber hose collapsing under suction. I dont KNOW that this is occurring. I DO KNOW that once in years past it occurred in an automotive application, where the rubber hose looked fine, until you took it off and looked through it. Guy was supposedly street racing and mixing octane booster and it literally eroded the liner to the point where the nylon braid was beginning to show. YEP===lots of debris in the filter. He thought it was bad fuel.

So---sorry for the long explanation, but troubleshooting this shouldnt be as difficult as it seems. YES, by all means, its a pain, and painstaking.

Tom
 
I may have misunderstood your last post. Was the drop in pressure present on the mechanical gage too? Have you tried disconnecting all the hoses and blowing them out with air? Any chance the red cube is plugged?

Rich....unless i?m Completely out to lunch, the flow test @ feed to engine MECH pump which measured @ 1/2 gal=90 secs....which equals 20 gals/hour flow; eliminates issues to that point.

The MECH psi gauge showed same as electrical sensor (just wanted to varify readings).
 
Fuel pressure from the electric pump is dependent on restrictions to flow. Not much restriction results in not much pressure, even though the flow rate might be 30 gallons per hour. The pressure out from the engine driven fuel pump is dependent on the internal spring. If that spring is weak, then pressure will be low. Not saying that is the problem, just explaining how it works.
 
Not to steal his thunder, but today at the airport I met a friend who was working on the problem with Ric. The mechanical fuel pump outlet fitting was obstructed by what looked to be shredded plastic or rubber. I suggested taking apart the old fuel pump and seeing if the diaphragm is intact. I hope Ric makes a report to Van?s or ROTAX. I?d hate to think there is a bad batch of fuel pumps in the fleet.
 
Not to steal his thunder, but today at the airport I met a friend who was working on the problem with Ric. The mechanical fuel pump outlet fitting was obstructed by what looked to be shredded plastic or rubber. I suggested taking apart the old fuel pump and seeing if the diaphragm is intact. I hope Ric makes a report to Van’s or ROTAX. I’d hate to think there is a bad batch of fuel pumps in the fleet.

Rich..thanks to Julian and Mark, problem found And “Miss Betty-Jeanne” is breaking the sound barrier again��. I am replacing fwf fuel lines/fittings with Aircraft Specalty’s set-up; also, will inspect the fuel pump and fuel lines to find out what the heck the shavings are...really weird where and how they plugged the an fitting....really glad we kept the plane close to field once fuel pressure started acting squirrely. Could have caused an off field landing.

Edit: Findings will be reported to Van’s; and if fuel pump is cause, full reporting to Rotax thru official channels.
 
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Ric,

Glad you found the problem. The pics Julian showed me were scary. Looked like almost total blockage.

I have the TS Flightlines after market fuel system. If you want to drop by the hangar and take a look before installing drop me a PM. The TS Flightlines instructions are very good, but it never hurts to see one in place.

Rich
 
NOTE---Since Steve at Aircraft Specialty and I worked on this project together, the hose packages are the same. So if you purchase it from Aircraft Specialty, or TS Flightlines, you are getting the same kit. Believe me its AWESOME to be working with a partner company, than to do it alone. Sharing of data is good for ALL of us!!
Tom
 
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