Automatic Watering of SIPs, Part 2

Prompted by a comment from Publius, I decided to follow up on my first post from last summer. Fair enough: I did call it Automatic Watering of SIPs, Part 1, which at least suggests I had more to say on the subject.

Problem is I'm not sure what to write. When I put up Part 1, I thought that I'd follow it with a list of all the "tricks" that I'd discovered along the way. There really aren't that many.

I talked a little bit about this in my response to Kathy last summer. Purging the lines of air bubbles is the hard part.



Here's how I do it.

First, fill the main reservoir--the yellow bucket in the picture-- high enough to let you gently push the connection between the hose and the siphon/supply line below the water level in the reservoir. In practical terms this means 3/4 full. Next, fill up all the SIP reservoirs, one at a time, with a hose. Now, if you attach a hose to the beginning--where the Hudson valve is suspended--of the one of the black siphon lines , open the other end of the siphon/supply line, and turn the hose on, you'll force out all the air with water. Once a full stream of water is coming out the end of the open siphon tube/supply line, abruptly close the open end of the line. Then, making sure that water is coming out of the end of each 1/4" whip, put each of the 1/4" lines into its respective SIP fill tube.

Lower the hose/siphon supply tube connection below the surface of the reservoir. Slowly unscrew the hose from the supply line, being careful not to let the hose kink, while the water is still running through the hose.

Now that all the individual reservoirs are linked via siphon tubes, you only need to control the height of the water in the main reservoir. Figure out the right height for your Hudson valve and you're done.

Last year I used a 5 gallon bucket as my reservoir. It has a relatively small surface area, making it hard to submerge the hose/siphon tube connection below the water level in the bucket without kinking the hose. I found out that this causes the water to stop, briefly, and introduces air bubbles. Not what you want.

To make it easier, this year I'm going to use a longer, flatter reservoir. Probably a 14 gallon Rubbermaid tote. This will let me lower the connection between the siphon tube and the hose below the waterline without any hose kinks/air bubbles.

Whenever the system isn't primed, it stops. You'll see the plants droop, and you know it's time to flush it out and get rid of air bubbles. That happened about once a month last summer and I'm not sure why it did. It might be the fill tube that goes down into each SIP is moving around too much. Or the 1/4" whip that goes into each tube gets pushed/bumped and no longer sits in the water reservoir . As a safeguard I'm trying to figure out a way to be able to see the level of water in each tub. I might put a clear vertical cylinder in the middle of each siphon line, mimicking another sip in the loop. That way I could quickly tell if it's gone off.

Any ideas on what else I could do?

There are (at least) a couple of limits to what I'm doing. The first is that the SIPs need to be on roughly the same level. In my case, since my individual SIPs have reservoirs 5" tall, that's the maximum height that can separate the highest and lowest SIP--on my slightly sloped roof--being regulated by one Hudson valve. The second thing is about the priming process. It determines how you lay out your piping system.

I found that you need to restrict the number of SIPs on each siphon line to a maximum of 12. The reason for this is that at some point there's not enough water coming out of the hose to fill the 1/2" main line and all the 1/4" whips that go to each SIP at the same time. And that's the only way to get rid of all the air bubbles: fill the entire section of siphon tube with water. Basic math can help here. The total cross sectional area of all the whips can't be greater than the cross sectional area of the 1/2" main line. Due to frictional losses, the area of the whips should be less. How much I don't know. Trial and error or a clever engineer could give the answer.

All this is by way of explaining why there are three black 1/2" polyethylene lines coming out of the yellow bucket in the photo above. Each of those lines runs in a loop around 10 SIPs. Since I have 30 planters on my roof, I have 3 main supply/siphon lines.

Guess I did have something to say.

Thanks Publius.