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brownhouse cistern installed
Wednesday, October 28 2009
Despite heavy rains throughout the day, I managed to install the steel girder shelf for the brownhouse cistern. Because of the way the girders rose up above the level of the shelf, the cistern couldn't simply be slid horizontally onto it, and this made rigging the PVC pipes from the roof gutter water supply system difficult. I had to measure carefully and pre-attached a threaded PVC fitting into a hole I'd drilled in the side of the cistern and then position that fitting in line with a pre-drilled hole in the wall, hoping it all lined up, and then coat a pipe with PVC glue and stick it through the hole from outside the brownhouse into that fitting. As it happened, all my measurements were within an eighth of an inch of where they needed to be and this all worked. The perforation in the cistern's side is near its top, reducing the pressure of water on the junction. But I still took several precautions to prevent leaks, knowing these would be hard to correct if they showed up later. I used a NPT tap to thread the hole in the HDPE cistern and then tapped a similar hole in a thick piece of plastic which I used as a "nut" on the inside of the cistern. I pre-wrapped the threads with teflon tape before screwing in the PVC fitting, and I gooped plenty of silicone aquarium sealant around the junction.
Unfortunately the rain quit just as I was finalizing my cistern installation, meaning I couldn't see it in action as it collected rain water. The cistern is designed to fill to its feed point, which is the same height as the PVC system coming in from the gutter. Slightly above this level but outside the brownhouse is a drain spout, ensuring that the reservoir does not overfill. The spout is actually positioned at a height ensuring that all the PVC pipes outside the brownhouse always contain a top layer of air, thereby giving ice headroom to freeze into. (Refer to the following diagram.)
Despite the lack of rain, I couldn't let my new cistern go untested. I wanted to make sure the gutter collection, anti-overfill technology, and girder-based support system all worked. So I took a garden hose and used it as a siphon to take water from a rain barrel at the northwest corner of the house and deliver it to the roof of the brownhouse (about 60 feet away and perhaps 15 feet lower in elevation). Over the next several hours, the slow trickle from the hose (matching the runoff of a vigorous downpour on the brownhouse's tiny roof) gradually filled the cistern to its feed point and then the water backed up and flowed out of the drainage spout, precisely as it was supposed to.
I'd used only quarter-inch particleboard as decking beneath the cistern, and under the weight of the water this bowed downward a bit between the girders and the two straps of Cor-Ten steel I'd run perpendicular to the girders. But everything seemed to be stable. And there were no leaks from the feed point. I declared the whole thing a success.
Brownhouse cistern.
Here you can see the girder system clearly.
Plumbing collecting water from the north side of the brownhouse.
Note the overflow spout.
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