Help processing catch cup results


I just performed a catch cup test on my Flex Daily front lawn zone and need some help processing the results.

Duration: 60 mins (I was watering in GrubEx1, so it was a convenient time to do a longer-duration cup test)
Heads: All Hunter PRS40
Nozzles: All Hunter MP Rotator MP1000

Here’s my zone settings:

And here’s my catch cup results (in):

My cups only measure in inches, so I had to do a conversion to mL (inches_collected * cup W (in) * cup L (in) * 16.387) to plug my results in to using the area of cup opening:

It gave me a uniformity of 43%, which is pretty bad, but considering cups 1, 4, and 8 were pretty wacky, I understand why. I’ll have to do some adjustments with the head coverage. The head below cup 1 is in an absolutely stupid spot and causes so much overthrow to the left, which is a rock path, so all the water that’s overthrown just flows out to the sidewalk and to the drain. But I need it to throw water pretty far to give head-to-head coverage with the adjacent heads.

But really, my question is this:

How in the world am I getting a precipitation rate of only 0.05 in/hr? It’s also telling me my runtime is in the ballpark of 800 minutes :joy: The nozzles (with double coverage) are rated for 0.4in/hr according to Hunter, and the results clearly show anywhere from 0.2 to 0.85 in from the hour test. Am I reading that result wrong, or putting in the cup data wrong?

You needn’t convert to ml to do the calculation. Your spreadsheet above has already done it. Your Nozzle Inches per Hour (Precipitation Rate) is 0.465" per hour. That’s the value that should be used in Rachio.

As to the conversion to ml, something’s wrong with your formula, assuming you’re using Orbit’s catch cups. No way are they 1.438" x 1.315" at the top. They are like 5" in diameter (have some in the garage, but too lazy to go measure them). You use the top dimensions of any catch cup, because that is the area of precipitation being measured. From what I’ve seen online, they have an area of 16 square inches (which works out to a diameter of 4.51"). Meaning your calculations would be off by a factor of 16/1.89097 = 8.46 > 0.05 x 8.46 = 0.43"/hr, so that’s close (0.05 is rounded off).

Nah, I’m using these cups:

I calculated mL in the spreadsheet specifically so I could put it into the watering schedule website.

I read a bit more on what values to use for nozzle inches. Like you said, it sounds like I want to use the average of my cups (0.46 in/hr), and then dropping the efficiency to 43% should add more watering time to help the under-watered spots? I guess I just have to make sure I’m not flooding the higher-values spots. I’ll have to adjust the throw of some of the nozzles.

I’m still super confused why the website is giving me 0.05 in/hr. Since it seems to be an Orbit site, is it just assuming I’m using the Orbit cups? I had to double-check and it never asked me the area of my cups, so that makes sense.

If so, your math seems to be correct that that’s probably the disconnect I wasn’t seeing. That makes a lot more sense! Thanks!

The Average of 0.46"/hr should work well. While your efficiency is low, so are all of mine. I think it matters as much exactly /where/ you put the catch cups during the test as it does how much is in each. My personal feeling is that if you don’t notice some areas drying out due to lack of water, then the dispersion isn’t that bad, and you may not need to set the efficiency as low as 43%, thus over-watering other areas).

Yes, that is correct, it assumes you are using Orbit catch cups, which are calibrated in both inches and ml, and you enter the values in ml. Since the Orbit cups have an area of 16 square inches, while your cups are 1.89 square inches, the calculated values are off by a factor of 16/1.89 or 8.47.

Perfect. It makes much more sense now. Thanks for all your help!

And yeah, the positioning of the cups absolutely matters. I tried a mix of spots I know are double-covered and some that are hard to reach, like cup 3 in between the 3 trees. This zone is on a slope, so the efficiency is probably not going to be great as it is. My flat back yard zone is 60%.