# Pressure loss Hunter with above-ground MP Rotator



## pdefeo (Sep 10, 2019)

Hi everyone,

First time poster but I've been reading and learning a lot from this forum and irrigationtutorials.com. I'm trying to run some above-ground sprinklers to hold me over until I get an in-ground setup in a year or 2.

I have a 1" supply pipe and a 5/8" water meter. My static pressure is 60psi. I have approximately 25' of a 1" copper pipe running through the basement before it splits to a 1/2" copper pipe running another 25' to my outside hose bib. I'm using a 50', 3/4" hose off the hose bib to try and give me as much water as possible. I measured about 4.9 GPM using the 5 gallon bucket test at the end of the hose itself. I have Hunter MP3000 90-210 MP rotors on pro spray PRS40 shrub bodies connected to Orbit 1/2" spike bases.

When I connect the 1st rotor, I measure the operating pressure at 44psi which seems about right with these regulating bodies and I'm getting full range from the rotor, almost 30'. However, when I connect the second rotor/spike 25' away using 1/2" poly tube, the pressure drops to 36psi and the range decreases to about 27'. Adding a third rotor now drops the pressure to about 26-28psi with another corresponding range decrease to about 24-25'. The three rotors are set up as 90, 180, 90.

From all the calculations in the irrigation tutorials website and the information I could find on Hunter's website, I would think I should easily be able to run three rotors using 0.86, 1.82, and 0.86 GPM at the same time. What am I missing in my numbers? Thanks.

Paul


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## g-man (Jun 15, 2017)

Great description. The part you are missing slightly is the pressure losses. The hose end test with 5gpm, is the part that confuses ppl. The hose is an open end zero psi point, so all the energy is converted from psi to flow. But that's not what you want for the sprinklers. You want the flow that keeps the psi above 40, so the heads can spray.

So what is happening is that as you add more heads, you are increasing the gpm going thru the hose. As this gpm grows so does the speed of the water flowing, this then causes friction with the walls of the hose and takes away energy. But it takes it away at a exponential rate. You are loosing pressure the more water you want to flow (3.54gpm) and the pressure is dropping so much, that it is below 40psi.

All this is great info, but how to fix it. 1) switch the polypipe to 3/4 or even 1in between heads. 2) change the 1/2 copper in the basement to 1in with a 1in bib. I think those two things will greatly help you. Do the poly first since it is cheaper.


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## pdefeo (Sep 10, 2019)

Thanks g-man. That's what I thought, the extra flow was causing the pressure to drop, but I couldn't figure it out based on my numbers. As you can see below, being conservative with the lengths of the copper pipe to account for elbows and tees, I believe I would have the following losses...

Starting Static Pressure (psi) 60

Pressure Losses (psi) 
1st Head @ 90 deg 2nd Head @ 180deg 3rd Head @ 90 deg
0.86 GPM 2.68 GPM (+1.82) 3.54 GPM (+0.86)
ft 
5/8" Water Meter 0.2 0.4 0.6
1" copper tube 50 0.05 0.2 0.4
1/2" copper tube 50 1 4.5 7.5
Frost-free hose bib? 
3/4" hose 50 0.5 1 3
1/2" Poly tube to 2nd head 25 1 
1/2" Poly tube to 3rd head 25 1.5
---------------------------------------------------------
Total: 1.75 7.1 13

I took these values from the Hunter Industries Friction Loss Chart...
https://www.hunterindustries.com/sites/default/files/tech_friction_loss_charts.pdf

The Rainbird poly spec sheet...
https://www.rainbird.com/sites/default/files/media/documents/2018-04/ref_PESDR.pdf

and the following Dultmeier hose spec...
https://www.dultmeier.com/pdfs/tech-library/02Water8.pdf

Based on the above numbers (somewhat rounded up for worst case), I would hope to still have enough pressure to run the second and third heads at full 40 psi, unless that initial 5 GPM has something to do with this. The one thing I am missing is the loss through a frost-free hose bib, which could take me over the limit, and/or any loss through the Orbit spike. Do you have any idea what that could be? I couldn't find any useful information on that. Thanks in advance.

Paul


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## g-man (Jun 15, 2017)

The spigot will have more losses, also all the fittings, the spikes and the hunter bodies (not just the nozzle).


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## pdefeo (Sep 10, 2019)

Thanks @g-man. I figured the spigot will have the largest loss and I almost doubled the length of the copper tubing to account for the fittings and then some. I contacted Hunter and they said the nozzle was negligible but didn't give me an answer on the body. Another request to them for that info . The way a frost-free hose spigot is designed I would expect it to have a much bigger loss than a standard type valve, but I can't find any info on those. Do you happen to know where to get that info? Thanks again.


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## g-man (Jun 15, 2017)

I don't. Maybe check with Watts or a spigot maker.


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