PTFE Fuel line near exhaust

[lr172]

I would like to route my -4 fuel line from the servo to the spider up between the #1 & #3 cylinders (it currently runs up the back). I have a vertical sump with a vetterman exhaust. I need to run the -4 line between the sump and the exh cross-over pipe right in front of it. I have about 1.5" of clearance. The fuel line is a PTFE type with integral firesleeve. the hose will cross the exh pipe at a 90* angle

I can make a little stand-off to keep the hose about 1/2" away from the pipe. I can also wrap the hose with heat reflective material and/or additional firesleeve. Will this be enough to keep it from melting? Any other ideas to protect it? I can make a heat shield, but the hose will be touching the heat shield, so not sure it helps.

I appreciate any guidance or suggestions you may have.

Larry

[bret]

I have interest in your question also....how close is safe? Where's our fire wall flame thrower tester? Dan.......want to play with gasoline and high pressure?

[DanH]

I wouldn't do it. The problem is not so much a matter of melting the hose, but rather, constant vapor bubble problems. The fuel in the hose between the controller and the fuel divider is NOT at pump pressure, but at metered pressure. For example, if your idle fuel flow is 3 GPH, you would have 18 lbs per hour, and the charts say that equals 0.5 PSIG nozzle pressure. So, line pressure at that location would be 0.5 plus the spring pressure in the divider (can't remember at the moment; maybe one lb). Think you might boil some fuel at 1.5 psi?

My own is a lot more distant, but it's still insulated (over the integral fire sleeve) with some fuzzy firesleeve, and the nearest pipe has a big radiant heatshield.

[Raymo]

Tom of TSFlightlines has done several like you suggest. I plan to do the same, with his lines and assistance.

Give him a call.

[bret]

That is one shiny intake tube, I see you!

[lr172]

Originally Posted by DanH

I wouldn't do it. The problem is not so much a matter of melting the hose, but rather, constant vapor bubble problems. The fuel in the hose between the controller and the fuel divider is NOT at pump pressure, but at metered pressure. For example, if your idle fuel flow is 3 GPH, you would have 18 lbs per hour, and the charts say that equals 0.5 PSIG nozzle pressure. So, line pressure at that location would be 0.5 plus the spring pressure in the divider (can't remember at the moment; maybe one lb). Think you might boil some fuel at 1.5 psi?

My own is a lot more distant, but it's still insulated (over the integral fire sleeve) with some fuzzy firesleeve, and the nearest pipe has a big radiant heatshield.

Thanks Dan. I was considering this to reduce heat in that line (still have moderate idle issues). This routing would reduce my hose length by 8-10" and would put more of it in the cooler upper plenum air. Hard to say if the 1-2" of exposure to high heat would be worse than 3' of exposure to the 200* air near the firewall. I suppose that pipe is running 800-1000* at the point of contact with the hose.

Maybe I'll just stay with what I have.

Larry

[Raymo]

Originally Posted by lr172

Thanks Dan. I was considering this to reduce heat in that line (still have moderate idle issues). This routing would reduce my hose length by 8-10" and would put more of it in the cooler upper plenum air. Hard to say if the 1-2" of exposure to high heat would be worse than 3' of exposure to the 200* air near the firewall. I suppose that pipe is running 800-1000* at the point of contact with the hose.

Maybe I'll just stay with what I have.

Larry

I should clarify that the ones Tom has done may not be the same as your setup. Still worth the free call.

[woodmanrog]

In certified aircraft, the minimum distance a fuel line should be from an exhaust pipe is 3 inches. You could use a heat shield attached to the pipe to insure the fuel in the hose doesn't get hot enough to cause vapor lock.

[JonJay]

Your fighting Vertical sump with cross over exhaust. I believe the only option will be to the back if it is a Silverhawk servo. While it is advantageous to keep this line as short as possible, routing it out the back, up and through the back of the baffle might be the best compromise.

[TS Flightlines]

Larry---integral firesleeved hose is wonderful. BUT, you still need to use good practices to protect the cover from direct heat, like laying it on exhausts, or very close. Heat shields certainly help.
The spec is 15 minutes fire proof, and 5 minutes fire resistant. personally---I'd see what options you have for re-routing away from the heat.
Tom