I have a set of Schmidt diesel injection lines on my p pump 24v and three of them have cracked now they are about 4 months old now and one of them cracked #6 on a real tight bend and I thought well no bigger called them they made me pay for that line and said if I sent the old one back they would credit the money back no big deal but now in the last week while I was waiting for the line to come in two other lines cracked this time it was on long straightway the truck runs great otherwise. I bought the mild steel lines the small diameter but they should not bust on me?? I think it is a defect in the lines themselves

 

Did you install all of the clamps that hold the lines together? There will be a lot of vibration if they aren't properly installed.

 

Yes all the clamps are installed and none of them vibrate like they did on my old 93 when I took the clamps off and lost them all.. oops. The cracks are long ways on the lines split open not around and broken in two like if the clamps were gone. Cuz that's how they broke on my 93 it was totally different this cracks are like they split open from too much pressure but my injctors are fine truck runs great I'm calling Schied right now

 

I assume you never bent the lines instead of totally removing to mess with the injectors.
Bending is a sure fire way to cause them to crack.

 

I just bought the lines and put them on the truck I never bent them other than to bend them just a little to keep them out of any kind of bind I just bent them enough keep them from touching each other and so I didn't have to hold pressure on them any way to screw the nuts on there just so they weren't in a bind or touching anything

 

This is a pressure fatigue failure. It happens because the hydraulic pulsations inside the lines are fatiguing the line and the hoop stress initiates a crack that looks like an overcooked hotdog-- right down the length of it.

A bending fatigue crack will crack perpendicular to the line. A parallel crack is pressure fatigue (hoop stress).

The fuel lines you bought are cheap and improperly engineered for the application.

Usually, this failure results from simply using a cheap material, or the surface finish on the ID of the tubing is not fine enough.

The factory VP44 lines are highly engineered pieces, believe it or not. You can't just use some parts store mild steel lines and get the results you want. You'll need a high-quality alloy, bent to tight tolerances, stress relieved and heat treated.

I was the product development engineer for the HP fuel lines on the 2010 ISX, so I learned a bunch about plumbing for fuel at injection pressure ranges.

JH

 

So should I just buy new stainless lines?

 

Stainless lines have a much worse track record than the mild steel. Generally its the larger size stainless that cracks, very rarely do you hear of the .078" mild steel fail. I had a leak on one of my lines, but no cracks. I'd call them and get a new set of lines from them. I'd still recommend mild steel though.

 

Stainless has less ability to flex with hydraulic pressure over mild steel. Hardness and work hardening is an issue with stainless.

 

My lines are .78 mild steel! What's wrong with them? I did not reduce the injector pop pressure but at the same time I didn't think I HAD to I will tho if yall think I should. I know 2 people personally that have 24 v p pumps and neither are running low pop injectors but both are running stainless lines and have no problems

 

I did not want the big lines because they make the truck lips and this is a daily driver n supposed to be 12 v reliable but it really has proved to. E a pain in the wazoo! I certainly hope its not JUST me with these problems

 

Isn't there a rep for shied diesel that looks over these forums?

 

Call them and see what they'll do for you. If you've had three crack and they are relatively new, I'd think they might help you out with getting them all replaced. Pop off pressures won't cause the lines to crack, the peak injection pressures are roughly 4 times higher than the POP.

Bigger lines don't cause a lope on a p-pump like they do on a VP. I've got .093" lines on my dually now, and it runs buttery smooth, with the exception of the ridiculously sensitive throttle.

 

Banks, I also suggest you call Scheids, from time to time bad batches of material slip through, and knowing their reputation, they will want to know about this failure, yours are likely not the only ones failed or going to fail.

 

I called them and they said send ny old lines back to them and they would give me credit back to my credit card for the lines but I still have to pay shipping both ways. And they always break on a Friday seems like. So I have them overnight and sat delivery is like 150 bucks I send the old ones back snail mail but this one at a time stuff is getting old I'm 4 new 1 good and one that I welded and is currently not leaking but tomorrow is a new day yet