I have a zone that takes 40-45 seconds to pressurize and actually start spraying in the zone. I’m on city water and these are all fixed heads. It’s on a slight incline and my best guess is the zone completely empties after it shuts off (which I see evidence of).
How can I best adjust the system for this zone? Adding 60s to the runtime would make the zone think it’s providing more water than it is. Adjusting the water output per head doesn’t make sense because it’s not a linear change (0 water for first 45 seconds and then full spray for the remainder of the run time).
I would decrease the Nozzle Flow in/hr by the same percentage that your 45 seconds ends up being of the watering time for that zone. Say your Nozzle Flow is 1.0 "/hr (I recommend you actually measure the flow with catch cups or measuring flow & area, but for now assume it is correct). And you’ve set all your other variables properly, and say that Rachio calculates a watering time for the zone of 40 minutes. Given all that, you are actually watering only 39.25 minutes due to the delay. (This is for Flex Daily or Flex Monthly, but especially Flex Daily.)
So, you’re under-watering a bit. You could just change the time to 41 minutes, and be really close to what you want (that’s what you should do with a Fixed schedule). But changing time directly with a Flex Daily or Flex Monthly schedule is not recommended. So - I’d reduce the Nozzle Flow by the same amount:
39.25 / 40 x 1.00 = 0.98"
Rachio will then recalculate the time based on the lower flow, increasing the time a bit, in this case to about 41 minutes rather than 40.
This “correction” will be much larger if the watering time is much shorter; a 10 minute watering time would require about a 10% change rather than a 2% change, so it becomes more critical then.
It should be noted that Flex Daily always waters for the same time and same amount of water, so it’s easy to correct like this. Flex Daily times will vary some, but I think this would get you in the ballpark.
Hope this helps.
What kind of valves do you have? What are the signs of the draining system are you seeing?
The slope creates a back pressure on the zone valve, and it seems your current zone valve is not designed to handle it, thus allowing the water to flow backwards while the valve is off.
Some manufacturers are now releasing a “reverse-flow” valves which are much better at handling the back pressure. For example CPF100 Rain bird valve home depot (link). Be sure to look for reverse-flow on the box.
In short, changing your zone valve to a reverse-flow model should allow the zone to stay mostly full, reducing the time to pressurize.
Signs of drainage are that the lowest (elevation) sprinkler head has water draining for a while after the zone runs. Area surrounding “floods” (relatively). During startup the highest (elevation) zone sputters till the whole zone gets pressurized. No water is leaving the zone, but the zone empties into the yard.
I have a sloped yard and I installed Rainbird SAM rotors in the lower areas as I felt like I was wasting a lot of water. They are designed to keep the water from leaking after the zone turns off and then the next time the zone runs, it immediately starts again. These do complicate winterizing the system as you need to make sure the water leading to the SAM rotor/sprayer empties. The big box stores don’t carry them but my local STI and Ewing Irrigation sells them.
Here is an example where you can read about them. They make SAM rotors and sprayers.
The same thing happens to a smaller degree on my sloped front yard. It takes may 15-20 seconds or more to get going, and closest heads always start first. I just assume the water drains out of the heads, as they are all lower than the valve. No big deal for me. But the OP’s delay is longer, and with shorter durations it could make a big difference.