In a large installation there could be well over a mile of wire going to a single valve
(first find the red-green stripe with the white circle on it, etc.). However, after two years underground, those coloured wires become all the same colour. The nightmare grows even bigger when you realise each one must then be tested.
Low-Cost, 2-Wire to the Rescue
RECENTLY, another option has come on to the landscape irrigation scene, which can, among other things, vanquish the prospect of the above nightmare; a plug-in adapter that converts the multi-wire to 2-wire. These adapters feature a single pair of wires that run from the controller out to a valve, then from that valve to the next, and so on. Instead of a web of wires going from the controller to its valves, two wires travel from the origin, at the controller’s adapter, to the last valve in the network.
As you might imagine, the effort to connect a 2-wire system is much less than a conventional system. The planning alone becomes a rather common-sense process. The 2-wire takes the most direct path to each valve with as many branches as required. Another nice feature is that the 2-wire technology does not require special equipment. The valves are the same as in any other installation and the wire is the standard irrigation variety (perhaps a slight bit larger gauge than in a conventional installation). The waterproof connectors are standard, as are the irrigation valve solenoids.
Other than the controller, the only special component is the electronic module next to the valve, called a decoder that identifies it as valve #1, #2, #3, etc.
This communication technology from the controller to the decoders makes the 2-wire process different from multi- wire controller technology. In 2-wire decoder systems, the controller applies 24-30 Volts to the entire path of wires. The valve stations, each attached to a decoder, have their own unique address.
Days OFF!
The controller impresses on the 30V, a signal with a sort of telephone number, in search of a particular valve. The decoder with that number closes its electronic switch and allows the 30 Volts to pass through to activate the solenoid.
Troubleshooting
Let’s take another look at the JCB scenario, described earlier. If the pair of wires is cut somewhere in a 2-wire arrangement, the whole system would be disabled, following after the point of the break. Would the multi-core controller system not fare as well, or better, than the 2-wire, since there are individual wires going out to each valve? No. This is because the multi- core uses a common wire, which is connected to every valve, anyway. Once the common wire is broken, the signal is cut for all remaining valves. However, the larger issue is, if the common wire is severed in the multi- core system, you'll have a big job finding it. The advantage of 2-wire in this scenario is that the controller is able to locate the approximate point of the break. You would know, for example, that the break is between valves ‘X’ and ‘Y’. You would then need a ground fault detector to pinpoint the exact point of the break, but would have a specific reference point between those two valves.
Installers with experience of both types of controllers maintain that the bigger factor is labour and troubleshooting. If the contractor accidentally digs up 15 wires, it can take hours to repair - if they are really good. With 2-wires they simply re-connect the two wires and are back in business.
Expandability
The ability to expand and modify valve configuration is another big advantage of 2-wire. In a given job, you may have to run the wires in a conduit under a road or other concrete structure. What is helpful is that all you need is a
conduit that would accommodate two wires instead of a typical bundle of wires.
But now assume there is a change in design and all of a sudden need to add some more valves. You are using 30 valves and he want to add five. You will have to pull these wires all the way from the controller location through these conduits and get out to where the valves are going to be (and typically, they’re the most remote valves). That is a challenge. With the 2-wire system, you only need to find the closest two wires and just tap in from there. From the tap(s), just add more valves and decoders that have different numbers, then tell the controller they now exist.
Project Cost.
Up till now, the cost of the hardware to implement a 2-wire decoder system has limited it to larger installations, the controller itself costing something near £1,000, even at the budget end. Landscape multi-wire controllers, even with as many as 48 stations, cost a lot less. With the introduction of modestly priced plug-in adapters the landscape controller can be converted to decoders. With some makes, decoder technology can be added to an existing multi-wire installation.
The pricing of the adaptor and decoders when offset by the lower cost 2-wire cable and reduced labour makes this option comparable for installations with as few as 20 valves and a total combined cable run of 500m.
... or what Pitchcare contributors get up to out of office hours
I have a yellow labrador, aptly named Digger as he still digs up our garden despite being 6 years old. He and my wife Mandy must love to watch me repairing the damage, as I seem to spend a fair amount of time out there! I was pleasantly surprised by the number of beautiful parks here in London. They’re superb and I walk the dog as often as I can. I take along my walkman radio and listen to all the sport on Radio 5. I’ve always loved the radio (having the face for it) and it’s amazing just how far you can walk whilst lost in a
game somewhere around the country and not being bothered who wins or loses. If no sport is available, I listen to the world’s greatest Rock ‘n’ Roll band, The Rolling Stones instead. I plan to visit the USA this Autumn to see them in concert. Now I have a little more time off, I can explore London a bit more and find nice pubs to eat in while out shopping, that being Mandy’s favourite pastime!
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