Hi all,
I'm involved in a small nonprofit farm ("http://www.fftn.org":http://www.fftn.org ) that grows produce for hunger relief organizations. We're setting up a new field and, since we're all-volunteer, would like to find a way to automate the irrigation system. We're using a control system (of course <grin>), and drip irrigation which involves an network of irrigation tubes running down the crop rows. This system will use about a dozen valves to control water distribution, allowing sections of the field to be irrigated sequentially.

Here's the problem: I'd like to use a "field" bus (oh, forgive the pun) to simplify wiring of the distribution valves, which are dispersed over
a distance of about 1500 feet. Finding an appropriate valve has been a tough row to hoe (oh no, not another...).

We need approx. 1 inch valves, low pressure (say, 25 PSI), able to withstand the summer sun and other weather, and a fieldbus interface that can go the considerable distance involved. Unfortunately, talking with local irrigation contractors about such things elicits only blank
stares.

Is there a valve that is a compromise between the cheap plastic solenoid valves used for lawn sprinklers (with no bus interface) and expensive
stainless process valves? (Or maybe a valve supplier that would like to donate some of the latter?)

Ultimately, I hope to instrument the field for moisture sensing so we can do on-demand watering, thus answering the question "Why should a controls person never get involved in farming?" <grin>.

Thanks in advance,
Ken Crater
Control.com Inc.
[email protected]

 

Hi Ken

Since cost is an issue, and the world won't end if you get a little extra water, here's an idea for control on the cheap with commodity equipment. Use X10 with the power distribution as your "field bus". Valve box contains an X10 switch ($12.00) and a transformer for the valve ($low) and the valve(s). Control the head end with firecracker or other X10 software. Use a 15 minute interval with an all off in between so if you miss an off it doesn't run forever. The commodity "lawn sprinkler" valves are actually fairly reliable, they just look tacky. The cheap valves are also more likely to withstand freezing.
I would of course use a Linux system and cron for this, but you certainly could do it the hard way if you want.

Regards

cww

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Ken,

I'd have to agree that the cheap plastic valves are the way to go. In my experience, they are rather susceptible to frost. In addition, they do NOT like sunlight, so you will need to either put them in a box or else make sure they're in the shade. The valves can be bought by the case from many different suppliers, and you should buy some extra valves for parts (cheaper than individual repair parts). The valves can then be rebuilt in
place (the body is not the part that goes bad unless you have a freeze or other mechanical damage). They also have a manual override that the bottom-of-the-line "industrial" valves don't have.

Another option is to look for surplus valves; but again, it's hard to beat the cheap PVC irrigation valves for least expensive cost of ownership.

Regards,

Willy Smith
Numatics, Inc.
Costa Rica

 

Try citrus & banana irrigation contractors!

Regards,
Phil Corso, PE
(Boca Raton, FL)

 

Ah.... aren't low cost solutions a challenge.... and fun..... and surely on this list there is enough knowledge to do it for absolute minimum cost.

Ken, I wouldn't necessarily look for alternative valves. The ones used in irrigation are used because they are not expensive. It is very dry during summer and temperatures get very high where I live so almost every home has automatic
water reticulation for gardens and lawns. The plstic "retic" valves are in fact quite reliable but here they are installed underground or in the shade. Maybe one of the retic companies or someone else would like to prove this statement right or wrong. Some valves are installed in inexpensive plastic valve boxes. Some are simply buried with a small plate of fibreboard or metal or plastic above them to protect them from tools and to provide a means of finding them.

PVC is used for main distribution up to and including main valves. Glued joints are used. It's easy to replace a valve if the design is done correctly... simply cut the old valve or fitting out with a hack saw, glue a new one in and add a short piece of pipe and a joiner... glued of course.

Polyethelene is generally used for the dripper side branches where the flow is low. This is done because the dripper offtakes can be done with punched joints. There are low cost valves for the offtake too.

In domestic systems it is normal to wire a common to all valves and an individual power wire from the controller to each valve and switch the power wires. Systems genarally use 24V DC. Electrical connections are in most cases simply done using
blue points or by twisting wires together. I soldered mine and applied heatshrink to the joints. Everything is under the ground. (Keep a good record/plan.)

You will obviously need power to each solenoid valve. The question is what is the most economical way to switch them. Maybe Allen Bradley or somebody would like to donate a system since it's a good cause.

To determine the most economical solution we need to know how many stations might ultimately be involved and some idea of the topology of the irrigation system because the wiring probably needs to follow the piping. Here the wiring is usually taped to the underside of the piping. It's protected by the piping and helps to identify where it is.

So... let's start with the challenge of using the two power wires for the network signalling..... hmmmm.... Someone may challenge me here and say why not do it with one wire and earth/ground return..... ????

It's theoretically possible to do it over two wires using a different superimposed
frequency for switching each valve and a frequency to provide feedback to indicate
that the valve is in fact on.... one little PCB per valve?

Someone might even come up with a system that has a huge commercial market.

C'mon folks........ think about it.

Vince

 

Suggest you try a S. FLA company that installed a like-system to track Manatee movements throughout Florida's waterways. Gates and Locks were also involved. The firm is:

Custom Controls Techology, Inc
"www.customcontrol.net":http://www.customcontrol.net

Regards,
Phil Corso, PE
(Boca Raton, FL)

 

Maybe the K.I.S.S principle should be invoked here?

Check with your local building supply company. They provide multiple zone irrigation timers specifically for the task you want to perform. I got one a few years ago to control the 16 different zones at the entrance to a housing development. The zones needed different amounts of water. The timers run on 115VAC and have a 24VAC transformer to control the 24VAC irrigation valves (standard irrigation parts). Each zone has an individual time adjustment so you can water different crops with different amounts. These gadgets are sequential, so if you want multiple zones on at once you need to be slightly creative, but no rocket science required. These clever controllers aren't designed to interface with anything except the water supply and the power circuit so leave your PLC and PC in the office.

Typical price for the timer box is around $200. Add cheap valves, wiring and plumbing and the system is complete. Average installation time for a 16 zone system is one man day plus the trenching/burying of whatever parts you bury. The valves are designed for direct burial and so are the other "field" components. The vendors sell rain sensors that turn off the system when the cup has enough water in it (soon to be a code requirement in many states).

 

If you do not like plastic valves the local HVAC supply will have small brass motorized valves that are used in home heating systems for zone control in individual appartments or rooms. Though rugged I think they should be enclosed for exposure to the weather.