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Fuel line test

UNCRV

Active Member
On the Rv12is I wanted to get an idea of what the community thought on this topic. I decided to test a couple of the fuel lines before I went much further on the build so I capped three ends and put a pressure gauge in the system as well as a valve and inflated the system to 50 psi. I found several leaks using dish soap and tightened those connections and pumped the system back up. After 24 hours it lost 10 psi. Is this acceptable or do I need to chase this down?
 
After I figured out the problem with this was the cheap pressure gauge I got the res of the lines installed. Is there any problem with pressurizing the entire system with the fuel pumps installed using air (minus the tank which is out of the plane at the moment). I don’t see why it would cause a problem with the pumps but wanted to check here first.
 
At a minimum

Have someone with a fire extinguisher stand fire watch for you. There's a recent, well known case for such.
 
I did leak down pressure testing and bubble testing with air on my -8 plumbing from the from the tank connection fittings to the firewall. It’s probably the best way to find small leaks. I was unaware of the fire danger. Look forward to hearing about that.
 

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Fuel line pressure testing........

.........inflated the system to 50 psi. I found several leaks using dish soap and tightened those connections and pumped the system back up. After 24 hours it lost 10 psi. Is this acceptable or do I need to chase this down?

I believe testing hose/line pressure to twice what you expect the system to handle is sufficient. That would be 20 psi for a fuel line as most will only see 10 psi in service.
 
I did leak down pressure testing and bubble testing with air on my -8 plumbing from the from the tank outlet fittings to the firewall. It’s probably the best way to find small leaks. I was unaware of the fire danger. Look forward to hearing about that.

Did you have the fuel pumps installed? That’s the only thing I was curious about potentially damaging.

Was this fire using air or was it using fuel? I’m curious about that as well
 
Yeah, sorry. Tend to scan versus read for detail these days which is not appropriate obviously, Read "pressurize with fuel pumps..." and skipped forward. Known by several names such as "in-service leak testing" in industrial world. My apologies.
 
Fuel pump installed. Limited pressure to 30 psi but I have an AFP FI fuel pump. I found a leak in the pump!
Leak testing is an art. It’s hard to define an acceptable leak rate. You are looking for bubbles that take 10 minutes to form 2mm diameter in pure water. Using a real leak detection fluid like “Snoop” helps because it forms small bubbles faster that look like fuzz. It’s not hard to get it tight enough that the pressure remains unchanged for days and you can see the pressure rise and fall with temperature.
 
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I believe testing hose/line pressure to twice what you expect the system to handle is sufficient. That would be 20 psi for a fuel line as most will only see 10 psi in service.

I could be mistaken but I think the 12is runs about 45 psi. With 4 lines installed with several fittings And pumped up to 50 psi I had a 2 psi drop over about two months which could have been from temperature drop also. However now I have added about 4 more lines plus multiple other fittings and the pumps and filters so wanted to check all that too.
 
I have 912ULS, so not familiar with 912iS engine or fuel system. I did however locate a stubborn leak in my fuel tank with use of ACDelco 1148963 Multi-Purpose Fluorescent Leak Detection Dye and a powerful UV flashlight. Worked a charm….
 
Happy to see the VAF team testing your fuel systems this way.

Fuel pump installed. Limited pressure to 30 psi but I have an AFP FI fuel pump. I found a leak in the pump!
Leak testing is an art. It’s hard to define an acceptable leak rate. You are looking for bubbles that take 10 minutes to form 2mm diameter in pure water. Using a real leak detection fluid like “Snoop” helps because it forms small bubbles faster that look like fuzz. It’s not hard to get it tight enough that the pressure remains unchanged for days and you can see the pressure rise and fall with temperature.

This is not the only pump that has leaked. I used 30 psi and have been promoting this test method for 5 yrs or so. It is really the best way to find the leaks. Pick your best detector fluid!

To the OP question about leak down overnight. It should be really small like a couple psi, if 10psi then you likely still have a leak. Always be sure to bench test the fuel pump assembly as much as practical . . . the fewer joints to test in situ is just a time saver.

Be sure to torque your 3003 tubing B-nuts not just tighten them, they can be over torqued, damage the flare, and result in a possible failure point in the future.
 
This is not the only pump that has leaked. I used 30 psi and have been promoting this test method for 5 yrs or so. It is really the best way to find the leaks. Pick your best detector fluid!

To the OP question about leak down overnight. It should be really small like a couple psi, if 10psi then you likely still have a leak. Always be sure to bench test the fuel pump assembly as much as practical . . . the fewer joints to test in situ is just a time saver.

Be sure to torque your 3003 tubing B-nuts not just tighten them, they can be over torqued, damage the flare, and result in a possible failure point in the future.

I finally found the leak was in the cheap crappy pressure gauge after pulling my hair out. Changed the pressure gauge and magically the leak disappeared. Ended up making two new lines on the interior side of the firewall because I was afraid I damaged the flair over tightening them. After removal I looked at them with a loupe and the flair looked ok but gave me more piece of mind. I have been tightening them to 75 in/lb since that point. After this it held within 2 psi for almost two months for that section of tubing. Funny how on a car I would put all this stuff in and not think twice about any of it but when in the air and you are depending on it to not fail it makes me think very long and hard about each step. I want it to be as safe as possible for myself and family.
 
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