Connecting ductile iron pipe to plastic pipe

[EddieWalker]

I've never met a drain pipe that was big enough. Eventually, Mother Nature will outdo herself to prove her point. The idea of reducing the size of a drain pipe goes against everything that I hold sacred in plumbing. How many sections of smaller pipe are you using to make this tempting? How clean is the runoff and how positive are you that nothing other then water will ever flow through it? How much would it cost to buy a 10 inch pipe and slide it into the bell, then use a rubber coupling to hold it together? Is there any cost savings in going to the smaller pipe?

 

[DerbyRunner]

I got a little more information. The source water is ditch water that is delivered to our property through a 1,000 foot 8" green pvc pipe system, then dumping into an open ditch that comes to our property. About 110 gals/minute.

The open bell end of the ductile iron pipe is near the ditch, and about 3' lower than the ditch. My employee envisions adding a concrete box in the ditch with a slide gate on one side (in line with the flow) and an 8" pvc pipe in a side wall. If the slide gate is open, water would flow (as it does now) through the ditch. With the slide gate closed, water would instead go in the 8" pipe.

This way, the 8" pipe could "tap into" the ditch water and get it routed over to the ductile pipe. It would require two 90 degree fittings as the only location to tap into the ditch is about 6-8 feet "downstream" from where the ductile iron is located.

After considering the impact of debris, I am wondering if this should be piped as a "closed system" or not. There is also an issue of silt, which needs to be periodically shoveled.

I've seen other implementations where an open concrete box is used to "tap into" the ditch water, then pipe it to another open concrete box where the ductile iron is located. The piping would connect the two concrete boxes, and each concrete box could be cleaned and shoveled out as necessary. Maybe also some filter screens.

Does this make more sense as an approach compared to a closed piping system? If it does then there would be no need to join the two types of pipe together.

 

[3Ts]

I would never ever reduce the size of a drain pipe. Since there is a potential for silt and possibly debris, I would use a box with a grate on the top to facilitate clean-out. There needs to be an inch or so of space under the pipe to allow for silt build-up. The box needs to be larger than the 10" pipe so the flow slows down and drops the silt in the box.

I vote for a concrete box with the pipes thru the sides and a grate on top. This way the smaller pipe can be used and easy access to it WHEN it gets clogged (not if). I had a drain pipe that an excavator put a kink in it so the pipe was now about 1/2" narrower at one spot and that is where debri built up, even with a screen at the inlet.

 

[DerbyRunner]

The 10" ductile was used because it was available. Everything else associated with this water flow is handled using 8" pipe (or open ditch.)

If open concrete boxes are to be used, I wonder how you size those to allow the best settling of silt and debris before entering the pipe. And for best sizing for cleaning out when necessary. There is moderate silt that comes with the water. But the majority of that (I think) is caught right as the water enters our property.

 

[chim]

About 6 years ago we did something sort of similar at our shop. There is a paved driveway that has a pipe under it so storm water doesn't get trapped on the one side. It was just a pipe with the ends exposed in a depression on each side. The downstream side is about 2' below the driveway and there was a narrow trench that ran from the driveway to some wasteland on the side of the property.

The inlet end of the pipe was always getting clogged with debris and there was a large puddle much of the time. We had a small precast catch basin (something like 24"x24"x30" deep) out in the one storage yard. We made a bar grate for it, poked a hole in the side, and slid it over the end of the pipe for the inlet side.

On the other side of the driveway we poured a larger concrete box in place, built a bar grate for it and extended a large PVC pipe from this box to "no man's land". The open trench had separated a good piece of our laydown yard for years, so burying the pipe made life easier for storing materials.

We did have the pipe openings far enough off the floor of the box to create a sump to catch debris. Although the plan was to periodically clean the sump, we never have. The water flowing through cleans enough of a path for itself.