What’s going on below? (Part 2)

In the second part of our feature on below-ground drainage, we take a look at material dos and don’ts, and common mistakes plumbers make in installations like this.

Material dos and don’ts
Renier Snyman, technical and product manager at DPI Plastics, said, “In a survey done by the Southern African Plastic Pipes Manufacturers’ Association (SAPPMA), it came out that, for sewer installations, PVC has 95% of the market in the smaller diameters.” Snyman said that this is because PVC is the right material for that application. Because PVC has a very smooth wall, the opportunities for scale to build up are limited and, because very little bacteria growth is supported by PVC, it is also quite hygienic. PVC is also light-weight, resistant to root-ingress and relatively easy to use on-site. “That all makes it very convenient to use,” Snyman added.

Common mistakes and what you should avoid
Mistakes and oversights can easily occur on job sites, especially when the pressure is on to keep costs low and speed up the installation. And, while some mistakes might not have such a big effect that it costs the entire project, others do. When it comes to PVC, HDPE and polypropylene pipes, one of the most important things to take into consideration is pipe stiffness. “For a sewer pipe,” Snyman explained, “for most of its life, it will be empty, with the pressure of the soil bearing down on it. And, if it collapses, it causes a blockage. So it’s very important that the stiffness is maintained.”

The integrity of the sealing on drainage pipes is also very important, as is incorrectly laying the pipe. When it comes to PVC pipes, if you don’t backfill (that is, refill an excavated hole with the material that was dug out of it) or compact the trench properly, it might collapse onto the pipe and cause blockages. Throwing unscreened material, like bricks and other site debris, into the hole when closing it up cause also negatively affect the integrity of the pipe.

Polypropylene pipes are more resilient when it comes to backfilling. According to a 2010 study conducted by the Virginia Centre for Transportation Innovation and Research, that even despite sub-optimal backfilling and compaction, polypropylene plastic pipes performed satisfactorily during their first year in service.

What is most important is that you, the plumber, understand the benefits and limitations of the pipe you plan to use, and that you follow the standards as closely as possible, in order to provide safe and reliable sanitation systems for the public to use and enjoy.

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