# Calculating Velocity and Pressure Loss



## FoldsPocketAces (Mar 16, 2019)

Hey guys, trying to run some numbers to set up my irrigation system. I am currently looking at an irrigation system the previous owner installed (or had installed) as I'm about to re-sod my front lawn of 1200sqft.

The irrigation system is split into 2 zones, each zone having 7 sprinklers. The PVC lines start at 1", down to 3/4" at each "sprinkler leg" and to a 1/2" threaded 90 below the sprinkler.

I did the bucket test at the spigot where the irrigation system ties off of (full bore spigot into bucket), from the main line, and if I did my numbers correct, I have 30gpm. I filled a 5 gallon bucket in about 10 seconds. I also have 65 psi of static pressure.

Am I correct in thinking this is way too high of gpm and pressure for running 1" lines, causing huge psi drop? How can I estimate how much psi my sprinklers will get. I am planning on running Rain Bird R-Van 14's and I am not sure if I require the 45psi regulates bodies or not


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## FoldsPocketAces (Mar 16, 2019)

I just read from another thread that i am actually calculating total flow. Since each zone only has 7 sprinklers, and the RVAN's GPM output for each of my zone is about 8GPM, I should use that number instead. So PSI loss on 1" for 8 GPM is about 1.6 psi loss and moving at about 3fps, and at 3/4" it's about 5psi loss moving around 5fps. This would mean I would need the psi regulated bodies to have my RVANs at the recommended 45 psi. Are my numbers correct?


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## TC2 (Sep 15, 2017)

Sounds about right, except there are possibly other areas of pressure loss, for example, a reduced pressure backflow can take off 8psi.

The Irrigation Tutorials website goes through everything.


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## TSGarp007 (May 22, 2018)

FoldsPocketAces said:


> I just read from another thread that i am actually calculating total flow. Since each zone only has 7 sprinklers, and the RVAN's GPM output for each of my zone is about 8GPM, I should use that number instead. So PSI loss on 1" for 8 GPM is about 1.6 psi loss and moving at about 3fps, and at 3/4" it's about 5psi loss moving around 5fps. This would mean I would need the psi regulated bodies to have my RVANs at the recommended 45 psi. Are my numbers correct?


If you don't want to replace the bodies, then you could also put a pressure regulator on your supply before the valves. If you got a regulator that brought it down to say 50 psi, you might lose 5 psi at the valves (should be able to look up the valve specs), then whatever you calculate in each pipe run (distance, elevation, fittings, etc). Might end up with decent pressure at each sprinkler without swapping out the bodies.

When you switch to the PRS spray bodies, do you have to replace the whole spray body, or just unscrew the top and replace that portion?


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