I haven’t found this specific issue elsewhere, and I may be crazy, but I’m seeing a huge difference between published emitter rates for drip lines with emitters vs “real” emitter rates using “catch-cup tests”. Of course I am converting from GPH to inches per hour (nozzle rates) based on the total area of the catch cups, just as when testing sprinklers.
Emitter tubing specifications have a number of values including GPH per emitter, emitter spacing, etc. But just WHAT is the actual emitter rate for such lines?
Not knowing if it is even relevant I performed a catch cup test on several drip lines in one of my zones. The emitter tubing I’m using have published rates of both 0.5 and 0.6 GPH. Each of 9 cups were positioned directly under a single emitter under 9 of my 11 individual lines and I made sure no water would miss the cup. My initial setup was for a 15 minute run. This needed to be abandoned after about 2 minutes as the cups were overflowing. I then emptied the cups and did a quick run for only 1 minute! Each cup has a capture area of 5.94 square inches and captured volumes ranged from 95.16 to 58.56 mL with a uniformity of 0.79. The resulting rates were 18.6 GPH or 80.3 in/hr! This is 30.5 times the published specification.
It is my understanding that, when performed with sprinklers, the result is then used as the input for Rachio’s “Nozzle Inches Per Hour”. But 80 in/hr seems excessive, so I determined a “per emitter” nozzle rate of 2.07 in/hr, which is still 3.4 times the published specification.
Bottom line is, am I overthinking this? Are catch cup tests even valid for drip emitters? Should I be using the published emitter rates, or my catch cup “per emitter” rate?
You’re right; 80 in/hr is 'way high. We’ll assume you’ve not confused emitter specs of GPH with typical irrigation flow rate calculations from GPM. If you can isolate water delivery through your home water meter, calibrate that whole drip zone together to see what’s really happening:
o Learn how your water meter dial works - if it has hands, how many gallons is one revolution? (Mine is 10 gallons per revolution, plus numeric wheels, yours might be different). Determine the total area you expect to be irrigated in the zone in square feet, perhaps with this:
o Find a stopwatch to do some timing. Your phone is likely to have one.
o With the zone running, watch the meter dial and start the stopwatch when the hand reaches the zero or top dead center position or zero last digit, whatever works.
o When the hand has gone around at least twice, stop the stopwatch when the hand hits top dead center again.
o Stop the zone and do some math (we’ll pretend you did 20 gallons by the meter in 4.5 minutes by the stopwatch for an irrigation zone of 500 sq. ft.):
Flow is 20 gallons in 4.5 minutes, or 20 / 4.5, or 4.4 GPM.
Precipitation Rate (Nozzle Inches Per Hour) is 96.25 x flow (4.4 GPM) / area (500 sq ft), or 0.847 in./hr.
Probably can’t get much better than that… no catch cups, no guessing, no matter what the published emitter rates are you know how much water is applied over time to the zone.
Thanks for the reply JB, and sorry for taking so long to respond.
I have again downloaded the linked spreadsheet and am looking carefully at it. The first two times I looked it over it seemed hopelessly inscrutable, but that’s really my problem.
It seems my approach is completely down the wrong path so I will try again. I can monitor my meter flow rate remotely, but to the nearest minute. I generally have run tested for ten minutes, discarding the first and last values as “filling the pipes” and "stopping short. I may up that to 15-minute tests.
My biggest problem is estimating an area. In may cases I have a single line snaking through the landscape. In others there may be a single line in two directions – how are those areas calculated / estimated? As a final example, that I see is covered in the spreadsheet, is the calculation for a single emitter.
I’m also looking at a 9 x 4-foot area (36 sq. ft.) with driplines spaced every 6 inches, 5 lines extending the length and 7 the width at 12-inch line spacing. Measured flow volume was 1.67 gpm yielding a nozzle flow rate of 0.0326 inches per hour – but I’ll run this through the recommended spreadsheet to check my math.
Again, thanks so very much. And I’ll let you know after I’ve tried the spreadsheet.
GAJett
@GAJett, don’t worry too much about the area. You should’ve seen this note in the spreadsheet. The area value is only used when the Rachio app. tells you how many gallons you have used, but has no impact on the actual irrigation. However, having said that the spreadsheet calculates the area value for you. Just use the area value that the spreadsheet calculates in put that into your settings.
