OK so what is the deal with these 2 types of fittings?? HD only has 3" fittings that say dwv and not sch40. I had to add a coupling to a pipe and the 3" dwv repair coupling leaked on my 1985 pipe, but on the new pipe was ok. Maybe I did a bad glue job I don't know. Can you mix dwv and sch40 fittings with old and new pipe? Supplyhouse also has a pvc dwv section and a pvc sch40 section... I don't get it.

Also, they had a 'coupling' and a 'repair coupling'. The repair coupling had no stops in it. Why is the regular coupling $1.50 and the repair one $5.50 (picture below)??

 

Schedule 40 pipe is rated for pressure and is thicker, DWV is not.
Example 3" nominal size:

Schedule 40....3 1/2 OD and rated at 260 psi max, min wall thickness .216"

DWV....3 1/4 OD and minimum wall thickness .070"

 

The answer to the second question is because for every "repair" coupling made (without stops) there are a million standard couplings made. Simple economies of scale.

 

Furd,

I couldn't think of how to put it into words. Thank you!

 

So this coupling and this coupling are no good for sch40 pipe?

I'm confused because these dwv fittings fit tightly on my sch40 pipe.

 

You're welcome, Norm.

If the coupling states it is for DWV (Drainage, Waste and Venting) then it cannot be used for schedule 40 piping. The same is true in reverse. It has to do with the pressure rating.

However, if the Schedule 40 you are using is NOT subject to pressure them you could probably get away with it. It would be wrong but may not leak.

 

Wow. I'm still blown away that HD would sell all these dwv fittings and sch40 pipe, if they are not compatible.

 

Mega-mart homecenters do lots of nonsensical things. The salesclerks at a homecenter are usually the last people you should ask for advice on any project. There ARE exceptions but they are few and far between.

I remember once a clerk in the electrical section told someone that for a service entrance they needed two 1/0 conductors for the "hot" wires and a 3/0 conductor for the neutral. The clerk's reasoning was the neutral had to carry the current from both hot wires so it needed to be twice the size.

 

Remember one thing about the non-rated DWV...it's commonly used in drain fields, or for underground from downspouts, etc. Matter of fact it's the vent in many porta potties. It can also be used when just the look is needed like for fake cannon for a play or similar (ask me how I know). And it's way way cheaper than Sched 40 or ABS. Depends on your area but out here ABS is about all that's used for residential, back in VA it was all PVC.

 

That makes sense, however I'm still stuck on the fact that the dwv fittings (well, at least what HD has labeled as dwv) are all 3.5" ID, meant to go right on a sch40 pipe.

 

All those fittings you show are the same. Ones a slip coupling and one is not... They are both DWV...

What is your question really?

There is another section in the home stores that sell same size PVC with a thinner wall. This is often used for drainage ( rain) and radon...

There is also another section in some home stores specifically used for underground sewer. This is called SDR 35. Its a different OD then PVC...

https://flexpvc.com/Reference/FullPVCPipeChart.shtml

 

If you haven't already, try and find someone who looks knowledgeable or just ask for a supervisor or manager at customer service and ask them. They may have restocked a certain area with the wrong items, or they could be located where you don't expect.

 

A 1/4 inch bolt (coarse thread) will not accept a 1/4 inch nut (fine thread). Both are available in most hardware stores and probably in close proximity to each other. You, the consumer, need to have some knowledge of the subject so a sales clerk, with less knowledge than you, doesn't sell you a bag of useless goods.

 

I was under the impression all the standard PVC pipe at the big box stores was Schedule 40. (you can get SDR 35 (green) in other areas, and Sched 80 from plumbing stores).

Any similarly sized fitting will fit any schedule pipe, but certain ones are specified for certain uses.
DWV fittings are curved to allow solids to move through more easily.
Sched 40 and 80 fittings are not curved the same way, and as Norm said, are rated to higher pressures.

Also, my understanding is that you can use Sched 40 fittings for plumbing vent lines, but not for waste lines (because of the lack of curves)


But maybe I've been led astray?