[szicree]

My understanding is that the hose from the mech. pump to the carb is just that, but why not use metal tubing with flares at each end?

 

[rrd1_99]

Subject to breakage..

All lines forward of the firewall should be flexible, as the vibration and relative motion of the engine will work harden any metal tubing, causing failure and that would be a bad bad thing with a fuel supply line.

Roger Barnes
-9A slow QB
La Grande Oregon

 

[szicree]

But this line runs from the engine to the engine. Furthermore, fuel injector and primer lines are hard.

 

[RV6_flyer]

Fuel injection lines are Stainless Steel. Copper is used for primer lines and they are typically replaced at overhaul time because they get brittle and will crack. Yes they can be annealed but typically it is just easier to replace. Primer lines typically will not stop the engine when they fail. They fail and will typically suck air making the cylinder lean or if they are under pressure, the fuel is a small amount and then all you need to worry about is the FIRE from the fuel on the HOT exhaust and engine.

BEST practice is to avoid the use of hard line and use hose from the fuel pump to the carb. It is done that way on fuel injected engines.

 

[scard]

Many of our tubing materials, just being attached in a vibratory environment, even without obvious major movement, will still fatigue at a surprisingly rapid rate.

 

[n5lp]

I vote for flexible line

In may of this year I had a failure of a rigid aluminum line between a fuel flow transducer, mounted on the engine mount and the fuel pressure transducer located on the firewall, nearby. http://www.vansairforce.com/community/showthread.php?t=29683
There was a crack right at the edge of the sleeve of the fitting. I replaced the rigid line with flexible line.

All I can come up with is that the distance was enough for some vibration to cause the failure. For the long run to the carb I would only use flexible line.