Cast iron out, plastic in

[Woodywhite]

I've got a 1960 18' Traveler with the original cast iron waste lines that have started to leak at the waste tank. Rather than repair, it seems a good time to replace the whole system. Reviewing the past posts, it seems like converting to PVC is a reasonable change. Given the age of my little trailer, it tends to bounce a bit so I'm concerned about vibration prematurely aging the plastic. Any of you have trouble with plastic waste lines instead of iron? It would be nice to lose a little weight (not just the traveler...) as long as cracking/leaking isn't an issue.

Thanks,
Bob

[Ultradog]

Your waste lines are probably galvanized steel and not cast iron. Some of the joints may be CI though.
Not that that matters much.
Others here could probably tell you more about the effects of road vibration on pvc but I would think you would have few, if any problems with it.
Keep in mind that the best way to avoid vibration fatigue is to not allow things to vibrate. An extra pipe strap or two to keep the pipe/s immobile would solve any potential problems.
The same thing holds true on power steering and hydraulic lines on tractors. They will fatigue and fail quickly if not properly secured. But using all the OEM brackets and securing devices will insure many years of trouble free operation.

[andreasduess]

The lines aren't cast iron - it's too brittle and too heavy. They are most likely steel.

[lewster]

I have never seen PVC used as a waste line in an RV. All of the current OEMs use ABS from the waste tanks to the outlet valves. 3" for black tank lines and 1-1/2" for grey.

[crispyboy]

Originally Posted by Ultradog

Keep in mind that the best way to avoid vibration fatigue is to not allow things to vibrate. An extra pipe strap or two to keep the pipe/s immobile would solve any potential problems.

I would be careful about making things too rigid - the piping needs to be secured yet still be able to "flex" a bit. I don't remember seeing the plumbing strapped down too tightly.

I have only seen ABS used in rv and mobile homes. I assume there must be more give in this pipe than ABS.

[Woodywhite]

Thanks to all of you for your replies. So now I'm feeling comfortable with changing to plastic. I'm not familiar with the differences between ABS and PVC. I tend to overbuild so I don't have to repair so soon later. From other threads it sounded like PVC is stronger than ABS. Do the current manufacturers use ABS because functional but it's cheaper? Is PVC stronger but more brittle over time?

Or are both OK and I'm making much ado about nothing and I should use whichever I can easily get?

Thanks again for your help. I gotta the old girl's plumbing back on line in time for Burning Man. Wife is coming along for the first time so i need to be little more civilized.

Bob

[awryawry]

In my experience, the solvent welding of ABS is more comprehensive and integrating than PVC joints. In the past, I have been able to chisel PVC joints apart, whereas a properly glued ABS joint is forever, and likely stronger than the pipe or fittings themselves. If you choose PVC, I'd advise joining it the same way that I would join PVC pressure joints: lightly abrade the mating surfaces, use PVC primer, apply cement to spigot -- hub -- then spigot again, join, and hold. For a TT I'd recommend straps or bridge supports at no more than 2' o.c., as well as at critical direction changes.

Plumb crazy,

wryawry

[seldencove]

My 1963 Ambassador has original abs waste lines, still working fine.....

[Woodywhite]

Got it. That kind of gives me a nod toward ABS. So my next stop is to see if I can get the proper parts in ABS. If not, I'll try PVC with proper prep.

Thanks for your input. I'll let you know how it goes.

Bob