[pczar3]

After reducing about a 40 inch piece of stainless tubing from aircraft spruce into a single 10 inch piece that finally worked I decided to take on one of the fuel lines. I have... make that "had" a new expensive imperial bender from ACS and tried to make the first bend. A loud snap and some words not to be repeated here is all I could here ringing in my ears! I spoke to ACS because the bender is listed as okay for stainless but when I went to the Imperial site it is not listed for stainless What do you folks use for bending tubing? The stainless is the 3/8 304 seamless with a .035 wall. Is this the wrong material for the FWF? If it is the correct stuff, what benders are you using? I already had the one break and those that look more suitable are much more expensive.
I was a mechanic for Chevy in my early years and never had trouble like this which leads me to my original question... what am I doing wrong?
Thanks,
Paul

 

[flion]

There should be NO tubing forward of the firewall (some exceptions are injection tubes or pushrod covers). Fluid lines should all be flexible. Aft of the firewall, it should be aluminum tube.

 

[Wayne Gillispie]

I used 5052-O from ACS in 6' lengths.

The only place I have ever used stainless and it was 1/4" was helicopter hydraulic servo lines. They have 3000 psi on them. I use Parker tubing benders, separate one for each size.

 

[Walt]

There should be NO tubing forward of the firewall (some exceptions are injection tubes or pushrod covers). Fluid lines should all be flexible. Aft of the firewall, it should be aluminum tube.

If that was true then why does Lycoming provide a nice SS line for the prop governor

 

[RV8R999]

no way! Only lines going from fixed connection points off the engine directly to the engine must be flexible because of vibration. Otherwise any other line can be tubing.

 

[TS Flightlines]

what was

the bender that you broke? Ive got a 370 and a 470, and bend .035 & .049 stainless with no issues. What part of the bender broke??
Tom

 

[flion]

If that was true then why does Lycoming provide a nice SS line for the prop governor

I did say there were exceptions. However, my prop governor line is not stainless, it's flexible. So is the line from my fuel servo to the spider. And there are also primer lines and probably other examples. As RV8R999 said, lines off the engine to fixed locations must be flexible. I would also point you to the ongoing debate about the brake lines; many feel the tubing is too susceptible to cracking and replace them with flexible lines. I stand by my statement; the kit comes with aluminum tubing for fixed lines but flex lines are recommended FWF.

 

[pczar3]

470

the bender that you broke? Ive got a 370 and a 470, and bend .035 & .049 stainless with no issues. What part of the bender broke??
Tom

Hi Tom, I just bought the 470 and the adjustable handle stops broke. I don't need to get into the flame war on tubing vs. flex. I used the stainless between the firewall bulkhead fitting and the gascolator, just like the Piper I fly. I just ran into a problem because the ACS site says the 470 will do stainless and the Imperial site does not have it listed in their product selector for stainless but the web page does! This was with the .035. 304 seamless.
Paul

 

[TS Flightlines]

wow-

no flame war Paul----just interested in how yours broke and mine hasnt.
Tom

Hi Tom, I just bought the 470 and the adjustable handle stops broke. I don't need to get into the flame war on tubing vs. flex. I used the stainless between the firewall bulkhead fitting and the gascolator, just like the Piper I fly. I just ran into a problem because the ACS site says the 470 will do stainless and the Imperial site does not have it listed in their product selector for stainless but the web page does! This was with the .035. 304 seamless.
Paul

 

[flion]

Sorry, Paul, when you asked in the first post if you were using the right material, I took that as a more general question. I don't feel that anyone has flamed me and I hope no one feels I've flamed them. As for using stainless for fixed lines or how to bend them, I can't help you - I don't have experience with stainless lines other than the hand-bent lines from my FI spider. And despite my comments about flex lines forward the firewall, I don't see a problem with a hard line to the gascolator; it's worked in lots of production aircraft.

 

[pczar3]

Handle position?

no flame war Paul----just interested in how yours broke and mine hasnt.
Tom

Not sure other than I may have been putting too much pressure on the handle and not on the stainless tube to help it around the mandrel. I was using it with the handle in the "up" position to bend past the 90 degree point and both of the locking ears left! I'll figure out how to get them bent for inside the fuselage because I prefer to have the stainless over the soft aluminum in areas where big feet can reach them.
Thanks again,
Paul

 

[Noah]

To answer the OP's original question, stainless tubing comes in different hardnesses - fully annealed (aka dead soft), 1/8th hard, 1/2 hard, and full hard, IIRC. In order to be able to bend the tubing, you need to make sure you bought something other than full hard, preferably fully annealed or 1/8th hard. You can not bend full hard stainless, it has been drawn to the point where it has very low enlongation before failure. Full hard tubing is made to be straight, never bent. Drawing, or work hardening the tubing increases its yield and ultimate strength, but decreases ductility and elongation.

Sounds like you bought full hard tubing to me.

 

[Lars]

Agree with Noah. Unfortunately ACS lists 304SS tube, both welded construction with .028 wall, and seamless with .035 wall. But they don't list hardness. Because of that, when I wanted some I went to the aviation department of McMaster-Carr, who does list such details. The 3/8" OD x .035" WT annealed tube I bought from them was easy to bend with my 470 bender.