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Lateral Pipe Sizes

3K views 14 replies 10 participants last post by  Some Sprinkler Guy 
#1 ·
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!

PH
 
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#5 ·
I have never heard of a minimum fps require to scour gunk from a pipe.

Now, gunk from my ex's trunk - that requires a whole hell of a lot more than 2 fps.

Personally, if all you are working with is 13 gpm, I'd stay with SDR 21 1" pipe for everything, lateral and main and design/install to the lowest sustained volume and pressure. The safest bet is to assume the worst and install for it.
 
#9 ·
My pressure loss would be 0 with 5 inch pipe... Unfortunately the budget won't allow for it (fittings are just too much for my cheap arse).

Anyway, thanks for the tips here. I've decided to go with 1-1/4" laterals, with 3/4" branches (to each individual head). Figure with only 2-4 gpm per head, the 3/4 will be fine, and actually save quite a bit of money.

Seriously though, I appreciate getting the insight from the pros on this forum. Thanks for your valuable time.
 
#13 ·
I agree. I don't know why so many people think they HAVE to drop down a size or 2 when running laterals... Use one size and all your fittings are the same. All your doing when you drop down is creating more pressure loss...
I hope you are one of my competitors bidding on this commercial job I am looking at with all 2" valves and main.

Your going to have like 8,000 foot of 2" laterals on your bid.
:cool2:
 
#14 ·
To be serious though, we dont go smaller than 1/2". Between my guys mis-sizing and stocking the trucks, and future expansion ability we opted years ago to use at least 3/4 and I cant say I mind it.

1/2" is just sort of chincy to me now.

Inventory and ordering pipe and everything is easier.

Once I looked at the hard savings on materials, the labor costs of jacking with the extra pipe size seemed to about even things out.
 
#15 ·
To be serious though, we dont go smaller than 1/2". Between my guys mis-sizing and stocking the trucks, and future expansion ability we opted years ago to use at least 3/4 and I cant say I mind it.

1/2" is just sort of chincy to me now.

Inventory and ordering pipe and everything is easier.

Once I looked at the hard savings on materials, the labor costs of jacking with the extra pipe size seemed to about even things out.
Thats supposed to say we dont go smaller than 3/4. Must be the cerveza typing. :cool2:
 
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