I recently got a set of the Orbit B-hyve Sprinkler Catch Cups to try to get some accurate numbers on precipitation rates and efficiency for each of my zones. Unfortunately what I’m finding is the results from that fail a basic sanity check when compared against consumed gallons (as measured by my smart water meter)/zone area (as reported from Rachio from my yard map). I’m using the Google sheet linked from the catch cup support article (How to use a catch cup test to assess Nozzle Inches Per Hour and Efficiency for Zone Advanced Settings). As an example, the results from the catch cup test for the first zone I did is .61"/hour. However the 15 minute test run used 244.4 gallons over a zone that’s ~600sq feet. That works out to a little over 2.5" per hour. (This zone is entirely fixed spray nozzles.) The second zone is a bit better, but it’s still off by ~25%. The catch cup test reports an average of .62"/hour while the 15 minute test used 110.6 gallons over a zone that’s ~950 sq feet (~.75"/hour). (This zone is a mixture of fixed spray nozzles and rotary nozzles.) While it’s possible my smart water meter is giving me bad readings, I’m inclined to believe it’s numbers given they line up with other things I’ve tested. As a result, I feel like I’m not doing the catch cup tests right.
At this point I’m tempted to not bother with catch-cup tests and instead use flow and zone size data to calculate an average rate. It won’t give me efficiency numbers, but it seems like it will give me significantly better precipitation rate numbers. Thoughts?
I’d be tempted to agree with your assessment of catch cups. I now have a flow meter, but prior to that, I discovered the precise measurement of the zone AND precise measurement of flow from the house meter, while ONLY irrigating, yields by far the most consistent measurement of precipitation in the zone. And it removes any necessity of caring about nozzles (number, type or separation) or other factors. Most don’t like either of these procedures - measuring the zone to the nearest sq ft or trying to determine gallons per min from a home water meter. Do this:
o Pace or find a long tape measure or wheel to compute the area of the zone as carefully as you can. If zones overlap, measure at/to the middle of that overlap in both zones. You’ll NEVER need to do this again.
o Do your zone calibration by EITHER timing (there’s a stopwatch on your phone) a fixed number of gallons through the meter OR recording the gallons through the meter over a fixed interval of time. My experience is that the former can be done best by one person. For a fixed number of minutes, use 2 minutes. For a fixed number of gallons, use 20 gallons†. Calculate gallons / min to a tenth. You should only have to redo this calculation if you modify the zone’s plumbing or nozzles or your water pressure at the meter notably changes. The formula (imperial units) you need for this is:
Precipitation Rate (in/hr) = 96.25 x flow (gpm) / area (sq ft)
Enter the rate in the Zone Advanced Setting for “Nozzle Inches Per Hour”, to a hundredth.
† for example, with a 10 gal / revolution meter, with the zone running, start the stopwatch when the meter hits top dead center, then stop the stopwatch after exactly 2 revolutions. That’s 20 gallons divided by the minutes on the stopwatch, to a tenth… your flow to the zone.
I have well designed layout, so I have no significant variance in coverage, pressure, etc. All my large stations (rotors) or clearly delineated popup zones specify 70% or 80% efficiency. I don’t remember what defaults were.
My understanding is lower efficiency indicates a requirement to “over water” a bit to reach dead spaces in the zone, compensating for different style heads in same zone, bad topographical sprinkler layout, significant slope variation. Problems I don’t have.
I would rely on the cup catch test because if done right it is measuring what actually hits the ground in the zone. If you don’t think it is accurate you may not be using enough cups to get a big enough data set. The more data you have the more accurate the results. Measuring by flow and estimated zone size is only accurate if you have no misting and all water is hitting the intended area, which it doesn’t.
Could be. It’s more important know, as well as possible, how much water (GPM) goes into each zone. And precise area measurement is one component of calibration any user can do pretty easily - and it’s good forever, so I stress it for new users. If you can do those two, you’re good.
