Automate Irrigation and Maintain Current Controller


Hello All,
The short story is I would like to automate my irrigation system using my Elk M1, but I'd like the ability to flip a switch that would revert control back to the current controller.  I know this can be done, but I want to make sure I am not over, or under, thinking this. 
My initial thought is to have a secondary 24VAC power supply that will supply the power to the irrigation valves when in "automation mode".  I would use DPDT relays controlled by the ELK to switch between power sources and switch the valves from their current loop to the automation loop.  I'd wire the "automation" side normally closed so this is the default state and controller side to normally open.  I would then have SPST relays to individually operate each valve.  All of this would be controlled from outputs on my elk.  The switch would use an input on the Elk to switch states so that a maintenance person can use the controller.
I guess my question is, am I thinking correctly with the use of DPDT relays or is there a simpler way to achieve what I am looking to do? If this seems correct, can you recommend a place to purchase said relays?
Thank you,


Senior Member
Tangentially, I went with a Rachio 16 zone controller and could not be more pleased with it.  Set-and-forget operation and the added intelligence of using web data for adjustments.  I rarely ever use the app or Alexa voice control. 


How many zones do you have?  If this is just for the maintenance control, exactly what do they need/do?  For instance, do they just need to verify the zones work after performing lawn maintenance (just turn on the zone, check it/aim sprinkler heads, then turn it off)?


Hello BraveSirRobin,
The system has 7 zones currently with an 8 zone controller. Adding the switch is definitely just for maintenance purposes. Typical maintenance would be all the things you mentioned as well as winterization and turning the system back on in the spring. I just thought it would be nice to have a labeled switch for a technician and if we decide to move it may make it a little easier to put it back to its current manual state.



There are plenty of DPDT relays on Ebay.  
Here for years used two Rain8Nets controlled by Homeseer.  Over the years went to using an ARM cpu (Seagate Dockstar) and mcsSprinklers software and SSD drives and used one touchscreen above the old RainBird box to control it.  
I have though always been a bit paranoid about connecting my irrigation to my OmniPro 2 panel outputs.  Way back one lightning near by strike took out both Rain8Nets.  I had to replace them.  I then added lighting protection to the Rain8Nets.  The Rain8Nets were connected serially to a Digi Edgeport which continued to work fine after the lightning strike.


Thank you all for the advise!  After I thought about this some more I did realize I was over thinking this a little.  Anyway, I've got all the components I need, but I have a question regarding setting up the switch as an input.  Do I set the input as a "Zone Definition 30 - Keyswitch On/Off"? Do I set the "Operating Description" to NC or NO? I can wire the switch as NC or NO so I guess I'm looking for the proper combination between the switch and the Elk.  The idea is that when the switch is activated It will switch the proper relays and suspend any programming.
Thank you,