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My Pond,  "It's all Underground.."

I was really pleased with my design for a flushing system, but sadly "you don't get nothing for nothing".  In this case a pipe was required from the settlement chamber to the main sewer, a short run off only 50M to the nearest manhole in the driveway. 

It was a back-breaking monotonous slog the whole way..!  We took it in turns to dig a few inches, rest a minute and then dig some more.  Michael even duped his brother Philip into giving us a hand, as it turned out, on one of the hottest days of the year.  Philip, stripped to the waist, worked like a trogon all day with scarcely a break. True, we really made some serious progress,  but he's wise to us now and we won't be able to trick him again.  Back to just the two of us, and digging the trench would take the best part of two weekends and every evening in between.

When we finally did get it dug we were still faced with the task of installing the solvent welded pipe, before starting to fill the whole thing in again.   Up until that point I hadn't given much thought to the pipe, well pipe is pipe after all, how hard could it be?  That's when I discovered that nothing is ever simple, especially when building ponds.

To get to the point, it turns out that there are two different types of pipe which we could use, and two different types of solvent to boot.  The one recommended by all the Koi experts is ABS pressure pipe.  Comes in 3M, 4M, 5M and 6M lengths and it, together with it's matching fittings, costs an arm and a leg.  Everyone was telling my that I had to use this "high pressure" pipe as it could withstand water pressure up to several atmospheres.  Normal PVC soil pipe would simply never take the pressure.   So now faced with a bill for pipe 5 - 10 times what I had originally estimated I set about some more research into the subject.  

Class B ABS pressure pipe is rated up to 6 bar, (87psi) and is a very high quality product indeed, but what sort of pressures could I expect to achieve with my pond?  If we look up a few conversion tables we find that 1bar = 14.5psi = 10M of water 'Head'. As my pond is 1.5M deep  + 120mm for the bottom drain, say 2M to be generous, so 10 (metre of water in 1 bar) divide by 2, (depth of pond) = 5.  Therefore pressure in underground pipes = 14.5psi divide by 5 = 2.9psi,  well within the capabilities of standard PVC soil pipe.   Looks like a lot of Koi keepers are being taken for a ride when it comes to pipe work, or am I just an old cynic?

Anyhow, back to my pond, Michael returns from the Builder's Merchants with the first load of Grey soil pipe and we set about getting it installed.  A 3M length of pipe might look long when you are trying to load it into your car or van, but when laid a few in our trench we began to get worried about our calculations. As it turns out Michael had to make a few more trips to the Supplier, in all we used 30 lengths, 90M of pipe..!    (I know I said that the trench was 50M to the sewer, but for part of it's length it also carries an additional 2 pipes to be connected to the pond's bottom drains)