Sunday, March 29, 2009

Fountain update: flexPVC limitations

My dad came down today, and we got a lot done.

2.5 of the 3 lower manifolds are now complete, and the fountain plumbing is now good enough for the pool rebar to be installed. This is great news because it means I am nearly released from the critical path and we can go from having one amateur working two days a week to maybe three or four professionals working 5 days a week. I expect a speedup of at least 7 times!

The bottom manifolds are made of flexible PVC pipe. This stuff is made with two different plastic formulations coextruded. The first is rigid white PVC, just like regular pipes are made of, which is formed into a spiral. The seconds is flexible PVC (with Phthalate mixed in for flexibility), which fills the gaps between the coils. This stuff is a little tricky to work with.

The first problem is that the pipe arrives in coils. By the time you get it, the stuff has achieved something of a permanent bend. I was able to take most of this out by unwinding the stuff down the middle of the pool, where it got hot in the sun for a week.

I have not determined a good way to cut the flexPVC. I'm using my miter saw to cut my pipe, because it makes such nice clear burr-free cuts on the regular PVC pipe. On the flexible stuff it leaves a hot, smoking cut with lots of burrs that I clean up with a knife. The Phthalate is particularly annoying, because our chickens love to eat the PVC chips from the saw, and we eat the chicken eggs, and phthalate is bad stuff. So, the chickens are cooped up on days when I'm cutting flexPVC, and I vacuum up everything afterwards.

We're also having difficulty just measuring the stuff. Somehow we're making lot of mistakes where we measure, cut, and then find that it's not the right length. I think the basic issue is that we're trying to measure curved paths with a tape measure.

Joints are a little scary with the flexPVC pipe. I had a professional plumber recommend that we encase every flexible PVC pipe joint in concrete. Now that I've done a bunch, I agree. If there is any bending load on the joint when it's made, the pipe sits in the socket at an angle, and in a few of those joints I can feel that the PVC glue has not completely filled the space between pipe and socket. I made most of the joints with no load while it was curing, and let them sit for at least a day before putting load on them. Those joints I'm quite comfortable with.

Dad points out that if I have a few leakers, the leak rate will be very low due to the concrete barrier and very low pressure in the system (3-6 psi). The plan is to pressure test before gunite, but that is going to be hard to pull off. I'm concerned I'm going to have leaks in the plastic membrane which collects the water, and this will hide any leaks in the piping.

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