# First irrigation setup questions



## emsguy630 (Aug 8, 2021)

Hello all,

I am currently in the process of putting up the DIY irrigation system that Ryan Knorr shows in one of his youtube videos. (I'm hoping to have a permanent one installed within the next year or 2) I've read a ton of information including the irrigation tutorials website but still have a few questions. Maybe I am just making this more complex than what it is lol. Yesterday, I tested my water source and believe to have possibly found an issue with high water pressure, but I have not had any issues since we purchased our home 10 years ago so I will address that later. Below are the following results.

Static PSI from spigot: 110 psi
GPM from spigot: 8 gpm

I purchased (3) of the Hunter PRS40 with the 40 PSI regulator valve built in. I plan on running (3) mp3000-90 (1.82 gpm @ 30 ft radius @ 180 degrees) So if my math is correct, I should need a total of 7.28 gpm which should be ok with what water source I currently have. I do realize that I will have to take friction loss into accountability and may be only able to run 3 of the roto heads at once. I will be running a 3/4" garden hose from the Spigot to the first sprinkler and will daisy chain the rest. Here are the things that are confusing me.

The PRS40's say that they are regulated to run at 40 PSI each. Does this mean that each one will use exactly 40 PSI meaning that if I run 3 of these sprinklers, it will require a total of 120psi from the source which is above what the actual static pressure that I have available? Secondly, how important is the length and size of the hoses that I will use to daisy chain the sprinklers? My initial plan was to purchase individual sections of 25' hose and just use them to attach one sprinkler to another another, but due to cost, I am thinking about just purchasing a 100' section of hose and cutting it to required lengths and attaching male ends to both side. I would assume that if I were to cut say a 8' section of hose to run from one sprinkler to the other, I would have less friction loss as opposed to just using a store bought 25' section of hose? I am also assuming that using a 3/4" garden hose as opposed to an 5/8" garden hose to daisy chain the sprinklers together would make a big difference? My apologies if I am making this a lot harder than it needs to be. I tend to do that alot. Lastly, the recommended pressure range for the PRS40's are between 15-100 psi. Being that my static pressure is above the range for the sprinklers, is this going to damage them in the long run?

Thanks for everyone's help


----------



## corneliani (Apr 2, 2019)

First off, welcome to TLF!

As for your 110psi reading at the spigot... you're right, that's quite some pressure but it very well may be piped to bypass the PRV that protects the rest of your household fixtures. Some builders leave one hose bibb unregulated... check the other one to confirm this. In any regard, with 100+ PSI coming through a 3/4" meter you should be seeing north of 10 GPM water flow on the other end. This means your future permanent system should get better water flow (ie, more heads per zone) once you tap directly into your main line.

As for the question on pressure-drop across the heads... there is SOME pressure drop that occurs but it is nowhere near the full 40psi that the nozzle itself requires to function. Since the water stream is being restricted to a very small nozzle opening the 'working pressure' only drops a few psi per head. Imagine pressing your thumb on the end of a hose real tight.. you need a certain pressure to reach a certain distance, but that doesn't mean you'll exhaust the system pressure. If you were to blow a nozzle off then you'd see that dynamic pressure drop significantly!!

For system design you primarily need to account for GPM, once the static PSI is deemed sufficient. If you're running long lengths of pipe, esp smaller diameter pipe, pressure drop becomes more and more important.. which brings me to your last point. Larger diameter pipe = more water flow & less pressure loss. In this case bigger is usually better.


----------



## gorgedude (Jul 5, 2020)

I don't know what the rule of thumb is regarding gpm and zone design but I like to have plenty of pressure and volume. I have 12.5gpm at the valve box so I keeps my zones at 6gpm or less. You can get into a whole lot of calculus on this or just use trial and error. Most everyone sticks to the later method.


----------

