Simple Automatic Watering System (No Programming Required)

Motivation

I have about 8 blueberries on my terrace and my daughter loves them. In fact we are all really fond of blueberries. Blueberries will blossom in spring and early summer and produce fruit in late summer to early autumn. During this time they need a lot of care and attention, mostly watering with and without fertilizer.

Figure 1: Blueberries like this grow on our terrace. But they require a lot of love and attention.

This is a job for one person, every day once, because blueberries are a thirsty plant, especially if (and they should be) planted on the sunny side. But… how do we go on vacation if blueberries require that much attention? Can we even go? That was the question from my wife.

Surely, we have a very nice neighbor, who would be more than happy to lend us a helping hand, and she does, but this, I figured, would be a task for a home-improver like myself.

Approach to the problem

The problem is simple: Water needs to come in regular daily intervals to the plants (it wasn’t just the blueberries in the end).

Figure below shows the solution to the problem of automatic watering, the approach I took.

Water source

I wanted to use tap water, because the reservoir is unlimited and besides, I don’t have a large tank anywhere around. For this reason I needed to install a simple T-piece with a small on-off ball valve between the cold water flexible pipe and the dishwasher. That was my source of water.

Control unit

I promised, no programming is needed for this simple solution, and that is still true. But something is required to turn the water ON-OFF in regular intervals nonetheless. I used a timing switch like the one in the figure below.

Figure 3: Configurable timing switch.

This is all we will need to configure to turn water ON.

Water control

Clearly water needs to be controlled and for this purpose I would recommend a pressure independent control valve (PICV). PICV is a valve that will output constant volumetric flow regardless (more or less) of the differential pressure across it.

In short, this means that regardless of what the pressure inside the pipes is, flow should be more or less constant, depending only on the opening of the valve. Therefore the name “Pressure Independent”. In my case I used Danfoss AB-QM DN15, like the one in the figure below.

Figure 4: Danfoss AB-QM pressure independent control valve.

The AB-QM is a neat piece for this project, because it also has a manual setting, which should be used to partially restrict the flow of water, in case the valve you chose is a bit too big for your application. One DN15 AB-QM is capable of approximately 600 L/h (approx. 160 gallons/h) max. flow.

That is a bit much for most home applications, but as said, you can restrict the valve with the manual setting. In my case, I restricted the valve to approximately 20% and the flow was just right to keep it open for 10 minutes.

The actuator is equally as important as the valve, and I used Danfoss TWA-ZL 230 V/110 V AC, Normally closed (NC).

230/110 V AC actuator is important because you can simply plug it in the timer switch.

Figure 5: Danfoss TWA-ZL Normally Closed 230/110 V used in this project.

The “normally closed” property is even more important, because this means that without mains power the valve will be closed and if the power is applied to the actuator, it will open. This is a safety feature, because in case a wire gets broken or the electricity gets interrupted for whatever reason, your valve will stay closed. Otherwise you might have a flood just because there was a power shortage one evening.

Piping

For the piping I used pneumatic pipes with quick-release fittings like the ones in the figure. Those are Festo Quick Star fittings. You can use anything, as long as you can attach the valve to them.

Figure : Festo Quick Star pneumatic fittings.

Calibration

Once everything is wired together, we still need to set the valve timing to water at specific time of day and for specific time. For example, I usually water my plants in the evening and each plant takes about 10-15 liters (approx. 3-4 gallons) of water. This is useful to set the valve’s manual setting and actuator’s time when it is open.

As mentioned before, I had to restrict the manual setting of the valve to about 20%, so the water flow was low enough to have the timer set to 10 minutes of open.

The actuator has about a minute lag between the time you give it voltage and the time it opens up. The same applies to closing. After the voltage is disconnected, there is also about the same time for the valve to fully close tight.

For calibration, you will need a stopwatch and some patience and that should suffice. Just measure how much water flows in a bucket and stop the flow after you had enough. Remember the time it took and now set the timer to that time. That should be it.

Make sure you tested the system before you let it run itself.

Recap

With this simple setup you don’t need any programming knowledge to water your plants while you are away. Maybe you don’t even have to be away to use i and watering just became a thing of the past for you and now you have some more time to spend differently.

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