# Question about pressure in diy sprinkler set up



## Di3soft (Jun 13, 2020)

Set up a sprinkler system for my front yard reno and stupidly used 1/2 flex pipe for the whole thing.


Had bad pressure cause of all the loss in the flex pipe. Went out and bought 1" poly pipe and laid it down about 80 feet as a main line. Each sprinkler is off the main with about 12" of flex pipe.



Now my question. Each sprinkler spike is measuring only 30psi, even though I tested the pressure on the whole 80 feet of main at 60psi

My pressure off the hose is 60psi at 12gpm. What am I doing wrong? Shouldn't each sprinkler have very close to the 60psi? Since each one is right off the main? I looked at pressure loss by pipe size and over 80 feet at my pressure it would be less than 3psi.


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## Di3soft (Jun 13, 2020)

Based on this my total loss should be less than 4psi


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## Di3soft (Jun 13, 2020)

My bad had gone set to 10 in the previous one, set to 12 still less than 6psi total loss


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## g-man (Jun 15, 2017)

Do you have a pipe layout? How/where are you measuring the head psi? How many gpm per zone and what is your design gpm?


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## Di3soft (Jun 13, 2020)

g-man said:


> Do you have a pipe layout? How/where are you measuring the head psi? How many gpm per zone and what is your design gpm?


The lay out is simple it's in the pictures 50 ft then right turn for 30 feet. Measuring head psi by attaching a pressure gauge to the spike pass through each sprinkler measures 30psi not just at the end of the run . 11 gpm based on what I read about 3/4 cooper. There is no design but three heads total less 3 gpm.


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## Di3soft (Jun 13, 2020)

The 1" poly pipe is fed by a 7 foot leader hose.


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## Di3soft (Jun 13, 2020)

I've also connected each sprinkler directly to the hose and pressure measure at just under 60 psi cause of the flex pipe


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## g-man (Jun 15, 2017)

30psi before the hunter head or thru it?

Measure the gpm thru the hose at the longest point using a 5g bucket, just to get an idea.


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## Di3soft (Jun 13, 2020)

g-man said:


> 30psi before the hunter head or thru it?
> 
> Measure the gpm thru the hose at the longest point using a 5g bucket, just to get an idea.


Through it, I did do the gpm measurement at the end of the 1" run and it came out the same. Between 10-12gpm which makes sense based on small timing errors


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## g-man (Jun 15, 2017)

If you are using a regulated body (eg. 30 psi), then you should measure ~30psi thru it. What is the pressure at the hose (just before the head)? What issue are you trying to solve?


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## Di3soft (Jun 13, 2020)

1 is regulated at 30 the others are not regulated. I guess I'm just confused why when I connect directly to hose. Pressure reads 60 and not 30. Trying to solve the distance issue based on pressure in the docs it should be spraying further. Also is it recommended to put in a auto drain on the main line?


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## Di3soft (Jun 13, 2020)

I haven't measure the pressure at the flex pipe before the head I'll do that tonight.


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## g-man (Jun 15, 2017)

I think it will be wise to get a quick hand drawing done. It should help clarify what you are doing/seeing. It will help with diagnosis.


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## Di3soft (Jun 13, 2020)

@g-man

Didn't have a chance yet to draw it out but measured directly before the spike base right off the funny pipe. First sprinkler is 60psi, second sprinkler is 50psi and third is 40 psi. This is with all all with all the other blocked off


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## Di3soft (Jun 13, 2020)

@g-man thanks for all your help but I think I figured it out, I kept confusing static and dynamic pressure and difference from later and main lines, I read through the irrigiation tutorial again in the the stickied post and got a good understanding now.


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## Di3soft (Jun 13, 2020)

@g-man here is the layout with a legend on what pipes are what the heads being used are rain bird pressure regulated 30psi with rvan nozzles, total gmp for that section is 5.95pm at 30psi. Still not getting the full distance that I should get at 30psi.


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## Di3soft (Jun 13, 2020)

Based on this and 40psi loss per 100 feet of 5/8 hose, so 15psi loss from poly + 4psi loss from 10' of hose I should have plenty of pressure for 30 psi regulated heads.


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## g-man (Jun 15, 2017)

If you start at 60psi, then take out 15psi from the pipe, that's 45psi. From there you need to subtract the pressure loss thru all the fittings, connectors, body, etc.

By how much are you not getting full distance? If you remove one head from your system, do the rest get their distance correct?


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## Di3soft (Jun 13, 2020)

so the irrigation tutorials spread sheet has this for the error factors

Error factor: An adjustment value to account for manufacturing error, fittings, bends in the tube, etc. 1.2 is a good value to use for an irrigation system with barbed fittings. Use 1.1 if using the snap-in fittings where the tube is pushed inside the fitting where it locks in place.

so I thought that includes the barbed fittings. and what not. or is that a wrong assumption?


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## Di3soft (Jun 13, 2020)

@g-man also looks like im getting maybe half the distance it should, ill try removing a head later today.


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## Di3soft (Jun 13, 2020)

did not even think about the time on the hose bib, that thing was dropping gpm to 5 straight from the bib im getting much better results


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## g-man (Jun 15, 2017)

Spigot controllers and splitters have very small ports too.


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## RVAGuy (Jul 27, 2020)

When doing pressure calculations, you need to take the sums of the pressure drop to the critical run only (the one with the highest pressure drop). You can't just add the sums of all the pipes. The flow in the main will also not be 11 gpm in all sections. Just keep this in mind. What you are doing is the conservative calculation, but just be aware it's not realistic.


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