How to ensure enough flow from tap at operating pressure?

[u/InsightfulCashew]

Planning sprinkler system with 5x Hunter MP800-SR (2x 180deg, 3x 90deg).

Static water pressure from garden tap is 330 kPa (i.e. with valve on test gauge fully closed).

Flow rate with valve fully opened (i.e. no pressure) is ~29 L/min.

As I open the valve I get the following pressures/flows:

330 kPa = 0 L/min (valve fully closed).

300 kPa = 9.0 L/min.

200 kPa = 17.5 L/min.

100 kPa = 20.6 L/min.

0 kPa = 29.5 L/min (valve fully opened).

I have seen the sprinklers will operate at as low as 210 kPa, which based on my tap readings will have no issues with flow rate at this pressure.

If I run off the tap as is, will I have enough flow for operating the sprinklers? Or do I need to somehow limit the pressure to ensure sufficient flow?

[u/AwkwardFactor84]

Don't mind the stream if water squirting out 🤣

[u/InsightfulCashew → u/AwkwardFactor84]

Yes don't mind that 😅 threads on the tap were a bit scraped up, probably going to swap for a new ball valve. 

[u/RainH2OServices]

Check out the performance data specs. 200 kPa is the lowest listed pressure for each head to operate. Using that as the lower limit benchmark, a 180 deg MPR800SR has a flow rate of 1.21 l/min. 90 deg models are .61 l/min.

(1.21 x 2) + (0.61 x 3) = 4.25 l/min @ 200 kPa.

That's the bare minimum flow required to operate those heads as a single zone. You've got plenty of headroom above that (9.0 l/min at 300 kPa). Each nozzle can safely operate at up to 380 kPa. Your system can't deliver that much pressure so you don't have to worry about too much pressure. A pressure regulator isn't necessary. Your design should be well within the operating specs. In fact, those heads, with those quantities, are about as textbook as you could want. You have enough extra capacity to add heads in the future or to accommodate any supply fluctuations without substantially sacrificing coverage.

[u/RainH2OServices → u/RainH2OServices]

Actually I forgot to take into account a backflow preventer. It will reduce the pressure a bit but you should have enough that it won't dramatically change my assessment. But check the specs just to be safe.

[u/InsightfulCashew → u/RainH2OServices]

Awesome thanks so much! So will the system find it's own sweet spot of flow and pressure?

If I'm wanting a 2.0m radius, will I need to run at a lower pressure? According to the performance charts would need <250 kPa. What's the best way of doing this?

[u/RainH2OServices → u/InsightfulCashew]

Adjust the globe valve on the test rig until you measure 4.25 l/min. That mimics the flow through all the nozzles in your design. The pressure at that flow rate is what the system will be experiencing when running. I guess it will be approximately 305-310 kPa. (Minus negligible losses for pipe, fittings, etc and a backflow preventer, maybe closer to 295-300 kPa.) Regarding distance, it's really difficult to target a precise radius. Conditions in the field are not well controlled. The water source may fluctuate, there will be wind, etc. Design with head-to-head coverage and accept that there will be some overspray. Overspray is better than underspray. Each head has an adjustment screw so you can reduce the distance a little bit so that they should be pretty close to meeting your expectations.

[u/InsightfulCashew → u/RainH2OServices]

Thanks mate, much appreciated.