Need help figuring out my Pressure and GPM

[llO0DQLE]

I have an underground sprinkler system that was installed by the previous homeowner which needs to be redesigned in terms of sprinkler head spacing. I've figured out a design but now I'm not sure if my system can handle the number of heads I've planned in one zone. I've read Irrigation Tutorials (in part) but the tutorial is geared more towards designing your system from the ground up. I just wanna know how much my current system can handle.

Regarding Flow - my understanding is that you can't put too many sprinkler heads in one zone where their total flow exceeds your system's flow. I can add up the GPM of all the heads I plan to use to get my total flow but how do I determine my system's actual flow? Can I do the 5 gallon test off my yard spigot? I don't have a faucet in the basement which is where my water supply comes from into the house and where the system is tapped into. Irrigation tutorials says not to design your system based on this flow but at one point in the tutorial says you can do this to double check for limitations or something to that effect. I haven't fully grasped the concept of pressure and flow and all the details/cinsiderations surrounding these concepts.

Regarding Pressure - my understanding is that the pressure you end up with at the sprinkler head is the net pressure after all the pressure losses you go through with the pipes etc subtracted from your static pressure. Irrigation Tutorials says to call the city or measure with a gauge to determine your static pressure. Are the two methods equally acceptable in terms of determining your static pressure? If I use a gauge, can I do it off of my yard spigot? I think the tutorial says you can do this but said something about taking the reading from a faucet at the same level where the system is tapped. Again, the system is tapped in the basement right where the water supply is coming into the house and I don't have a faucet down there. My basement is not finished.

Furthermore, if I'm designing sprinkler head spacing based off of the sprinklers' advertised radii at the ideal pressure specified in the tech sheet, how do I know what my pressure is at the head to confirm if I can achieve ideal pressure since I already have a system installed and I'm not designing from the ground up where I can pick my pipes and other materials to estimate pressure loss?

Bottom line is that I'm wondering how I can make sure that my redesign will work in terms of achieving the distance of throw requires with the spacing I've planned.

[llO0DQLE]

Ok so I reread the sections about Pressure and Flow about 5 more times and I think I have a bit better understanding. I measured my pressure from my yard hose bib with a gauge and it's 60 psi. As I'm planning to use Toro Precision Nozzles which are designed to operate at 30 psi, I feel I should be fine. It's hard to say without calculating all the pressure loss but since I didn't install the system and I don't know the length of the pipes, it's probably not worth agonizing over as the system is working at this time with some zones on Rainbird 3500 rotors and some with Rainbird VANs.

Regarding Flow, I did the bucket test from the same hose bib and figured my flow is about 7.6 - 8.6 GPM. The range is due to the fact that it was difficult for me to measure properly as there wasn't enough clearance from the hose bib to the ground for my bucket to stand straight up so it was tilted a bit. I measured 39.33 seconds, which puts it at 7.6 GPM. The bucket was tilted forward which means it took longer for the water to reach the 5 gallon mark I drew on the back inside part of the bucket (opposite of the forward tilt), then after I removed the bucket from under the hose bib, I spilled some water BUT the leftover volume ended up right at the 5 gallon mark, which means that I probably was a few seconds late with stopping the stop watch. If we put it at 35 seconds, then flow is 8.6 GPM. Most of my lines from my main line to the irrigation tap are 3/4" and according to Irrigtiton Tutorial's chart, Max Available GPM is 11 based on 3/4" pipe size. In any case, the total GPM of 14 Toro nozzles I plan to use in one zone is 4.78. I figure I should be good with Flow as well.

What do you guys think?

[Green]

Was the hose bib you measured from attached to the irrigation system mainline?

[llO0DQLE]

Hmm...not sure. Sorry, I suck with this stuff. I can see most of the pipes in my unfinished basement. So basically, the water source comes out from the concrete floor, is connected to the meter, then diverts to a water softener and then right after that is where the irrigation supply is tapped. It seems that everything else for the house comes after where the irrigation line is tapped. The previous owner told me that the water softener was only added last year so it looks like the irrigation system was tapped right after the water meter initially. I can take a pic later when I get home.

[Green]

Ok. I think the main factor is pipe size. Does the hose bib you measured from have the same pipe size supplying it the whole way? And Is that pipe the same size as the irrigation mainline, or different?

[llO0DQLE]

The hose bib is supplied by what looks to me as 1/2" or 3/4" PEX for the most part. After the meter and the water softener, it's 3/4" copper before it become PEX for the main line of the hose bib. It's the one with the bronze valve in the pic.

[llO0DQLE]

So the main irrigation line is 1" PEX for the most part (thick line on the left), also after all the 3/4" copper piping.





Thick PEX (1") is irrigation mainline and then becomes 3/4" copper before going into the yard. Thin PEX (1/2" or 3/4") is hose bib line.

Seems like my hose bib flow test probably doesn't apply to my irrigation main line so maybe my flow is higher?

[Green]

Since your irrigation line is 1" and 3/4"...
and your hose bib line is 3/4" and maybe also 1/2"...
I would say you're right in thinking that the irrigation system has a higher flow rate than what you measured in your test at the hose bib.

[llO0DQLE]

Ok, so with my hose bib having at least 7 gpm and my nozzles totaling just under 5 gpm, and my irrigation line most likely being higher than 7 gpm, I think I should be good. What do you think of my pressure?

The part that I don't get with Flow, is that supposedly, your Maximum Available/Safe Flow is based on the smallest pipe you have. So for 3/4" copper, that's 11gpm. The tutorial says you can push more flow but aren't you limited by the size of your pipe and the pressure of your water supply?

Also, with pressure, say you have 60 psi static pressure, then you lose some as the water travels through the pipes and other sprinkler parts, how do you know how much pressure you end up with exactly at the sprinkler head? So if I want to use Toro Nozzles that operate optimally at 30 psi, how do I know I can achieve that and not end up with too much or too little? I haven't finished reading the whole tutorial so maybe it'll come clearer when I do.

Thanks for all your help thus far Green.

[Green]

I think your pressure is ok. 60 psi is on the higher side of what the rotors are designed to use for optimal performance...but then again, my neighbor measured over 80 psi where we live! I'm not sure about sprays...all I know is they're more sensitive. I'm not sure how the losses factor in as the pipes get longer and more heads are on the system, either. I just know that the two sprays I have are pressure regulated to 40 psi (Hunter PRS).

It's a little more complex with the safe available flow. I've said it before and will say it again...despite my 1" home line and 3/4" irrigation mainline, and high pressure, I cannot get the flow high enough to surpass my safe limit of 12-14gpm with my pipe. It seems to top out at just under 11gpm...no matter what the nozzles on a zone add up to, even if it's over 12. But, I have an extra shutoff valve in the line, a boiler drain, as well as a 5/8" home water meter...so all those pieces are hardware are self-limiting the max flow, I think. So in my case I'm not worried about exceeding the max flow.

If you want 30 psi for your Toro spray nozzles, get a 30 psi spray body...like a Hunter PRS30.

[Green]

As for too little pressure...I doubt you'd end up at under 30psi easily, in a zone that only has spray heads and isn't overloaded with them. I could be wrong...but that's my impression. Sorry I don't have a better answer.

[llO0DQLE]

So basically, if I want to ensure my sprinklers are operating at the ideal 30 psi, as long as I don't have too much pressure loss resulting in pressure going under 30 psi when the water reaches the sprinkler bodies, using pressure regulating bodies that regulate at 30 psi will achieve this?

[Green]

That's my understanding. As long as it's above 30.

[llO0DQLE]

Ok thanks for all your help.

[Green]

You're welcome. I'll be watching for updates.