Lateral Pipe Sizes
Hello, just a quick question for the pros on this forum...
I am a homeowner installing my own system on an acre. I want to make the system as robust as possible. The pressurized secondary irrigation system comes through a 2" valve, and averages 55psi, but can drop into the low 40's on occasion. Because of this, I have added more zones with a lower gph requirement, and plan on running two at a time when the pressure is good, but maintain the ability to run one at a time if the pressure and volume ever drop significantly. I have read the irrigationtutorials.com site and the Rainbird design handbook completely.
Originally, I planned on using 1-1/4 inch sch 40 laterals going down to 1" for each head. I know its probably overkill for a 13 gpm zone, but I want to minimize the pressure loss as much as possible, and allow me the flexibility to add larger nozzles if I need to. Both reference sources say that there is virtually no downside to using a slightly larger than required pipe.
Well, then I was at the local irrigation supply house, and the guy said that you must always maintain at least 2 fps inside the pipe to scour away gunky buildup inside the pipe. Irrigationtutorials.com never mentioned this, but if true I am looking at 1" and 3/4" (even 1/2"!) laterals.
So, the question is: has anyone ever heard of this 2 fps requirement, or is this guy drinking the same kool-aid as the guys who say that you'll lose pressure if you go to a larger pipe?
Thank you for your time, and for contributing to this great resource!