Dented copper tubing, how much is acceptable?

[cranetruck]

I have a fair number of dents and some kinks in the 1/4 and 3/8 inch copper tubing along the axles on my 8x8 and was wondering how much of a deformation is acceptable. Obviously any dent or kink will reduce the (air) flow, but by how much?
The military has classified leaks, some of which are alright to live with and other ones that must be repaired immediately, is there a similar graduation system for dents in tubing?

The copper used in the original tubing is hard and the easy to bend soft variety may not be so good for this application, so replacement with all the bends may not be that easy.

I'll post a couple of pictures later.

 

[WillWagner]

I'd say I need to see some examples to judge it, but as long as it isn't kinked in half, it is only 1/4 and 3/8 OD line, so the lines are probably just to activate things so there won't be much flow there, just a need to charge a device.

 

[cranetruck]

Picture of one of the dents.
This is line #1, which is to "activate" the air brakes, no brake fluid here. The wheels lock up on a gravel road without any load, so it works, but perhaps with reduced effectiveness....
(I'm in the process of replacing the loom and keep finding these dents)

 

[cranetruck]

Replaced the line with 3/8 air brake tubing...
Still would be interesting to know if some "dents" in copper tubing are acceptable.

 

[Jones]

Your hard copper tubing may have started out life as soft but has work-hardened over the years due to vibration.
Other than obvious sharp-edged kinks (folded as opposed to dented), I replace when the internal passage is reduced to 75% or less of original size.
Even if it's just a line to actuate a component like a lock-up; I prefer crisp positive engagement and disengagement-- not sluggish, maybe-it's-in-and-maybe-it's-not operation.

 

[m16ty]

Well I dented the line on the firewall going to the governor on my deuce when I removed the engine. It's dented much more than your pics and I need to replace it but I haven't noticed problems with it being that way. Anybody that has ever removed an engine knows which line I'm talking about. I've seen alot of trucks with this line dented and I'm sure that was the cause (engine removal).

 

[WillWagner]

I'd say there no issue with the dent you have there. Run it! Bjorn, is that monster road ready yet?

 

[cranetruck]

I'd say there no issue with the dent you have there. Run it! Bjorn, is that monster road ready yet?

Yes, except for insurance/tags. The tires did worry me for a while, but having de-mounted and mounted a couple, I have gained confidence in them. Extremely tuff and almost pristine on the inside. A local junk dealer is trying to sell the 395/85r20 MVTs I got, but it may be time to put them in the classifieds here...

About the tubing, like Leonard points out, kinks gotto be the worst, since they often crack at the edges. The pressure is only 100 psi in the brake lines and I'll test the line that was removed against a new piece of tubing for flow. I have a wind speed sensor that may come in handy for this.

 

[cranetruck]

Using an air speed sensor for a sail boat, I compared the dented 3/8" copper tubing from the 8x8 to a new 3/8" plastic air brake tubing. Air pressure was 120-125 psi.

The dented copper tubing: Produced an air speed of 30.2 knots.
The new plastic tubing: Produced an air speed of 20.7 knots.

Apparently, I just down graded one of my brake lines by some 30%!
Note: The copper tubing has 4 dents and one kink in it.

I'll run the test again when I have some new copper tubing.

 

[doghead]

I think you need to measure volume(flow), not velocity to see the true effect that the dents would have on the air-brake system.

It makes sense that with the same pressure, you have higher velocity air flow. The capacity to flow volume has been reduced, with dents.

In the original application, I doubt the dents were changing the brake function, very much. I might even guess, the original design specification, was more than is needed to function well.(typical military overkill ?)

 

[bigelk50]

Great work Bjorn! Looks like you need some more copper tubing. Amazing how the little things can affect ya, that often are over looked.

 

[cranetruck]

Based on Eric's comment, I went back for more testing and found that the aim is important, if the air stream is off only a little there is an effect on the speed. I was able to get the plastic tubing up to 28 knots, so my test is inconclusive, however the dents don't appear to have much effect in this setup.

 

[rmgill]

Come on Bjorn, just like the little dings on gofl balls, the dings on your copper tubing makes the air move faster...