That’s pretty cool. I just used a pi Zero W running opensprinkler along with a relay board to control my irrigation system. Now I can turn on my garden drip system from my phone 
Be sure to put snubbers across the contacts on the relays or you’ll bugger up their contacts over time. Those sprinkler solenoid valves can generate 400+volts of back-EMF when their fields collapse / power to them is shut off. I’ve seen relay contacts welded together from the arcing.
Good to know. I used this relay board which is supposed to be good for a/c restive loads, not inductive loads:
I probably should use this one instead since it has solid state relays with built in snubbers?
good for a/c resistive loads, not inductive loads
that’s even more good to know. Been looking to do some really interesting things with node-red, scada hacking and 3d printing. Love that the elegoo has a din rail mount on thingaverse (https://www.thingiverse.com/thing:4264897) but that 8-channel one looks interesting and might be easy to mount as well.
Depending on the coil load, some coils need suppressors. They can cause back emf as well.