Dual power source to sprinkler

[bkenobi]

This is not X10 related but it is automation of sorts.  I have a sprinkler system at my house that includes 11 zones. In the US, sprinklers run on 24VAC. I just replaced 2 ancient Rainbird brand timers with an Orbit B Hyve 12 zone smart timer. The old system was actually comprised of 3 timers (2 electeonic, 1 mechanical) and I'm keeping the most archaic for now since the manual timer was used on the garden.

The question is, if I wanted to have the garden sprinkler controller by both the mechanical and smart timer, can I simply wire them in parallel?  If one is on and the other off I'm sure it would work. However, does feeding 24vac to the back side of either the mechanical or Orbits timer pose issues?  Since its  AC, I cant just install a diode so are there other ways?

[brobin]

If indeed that arrangement did cause a problem (not sure why it would), you could have each controller operate a separate 24vac coil relay that controls the zone.  The relay outputs would be in parallel.
I've had a B-Hyve system since they first came out and I'm very happy with it.  Out of curiosity, what's the benefit in keeping mechanical timer involved when you can just tell Alexa to turn it on?

[bkenobi]

No alexa here, but it's just a simple dial that we've always used. To use the b hyve we have to open app so less effort to walk to basement. I was thinking at some point I'd try the smart water on that zone and if it works well, id never use manual b hyve or mechanical.

As for the relay comment, I wonder if a dpst relay for ac trigger exists.

[brobin]

$15 on Amazon.  Ought to do exactly what you want.  2 relays in one package.  Just tie the outputs together.
https://www.amazon.com/Electronics-Salon-SPST-NO-Module-Control-Voltage/dp/B01B60RZPA/ref=sr_1_6?dchild=1&keywords=24vac%2Brelay&qid=1624152896&sr=8-6&th=1

[bkenobi]

That looks pretty much exactly like what I was thinking. I'll check if there will be notable WAF, but looks like a win here. And its showing for $13 for me so even a couple dollars cheaper.