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  #1  
Old 08-11-2010, 09:43 AM
BrasiliaFlyer BrasiliaFlyer is offline
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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!

PH
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  #2  
Old 08-11-2010, 09:50 AM
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DanaMac DanaMac is online now
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Never heard of that before. But we don't get a lot of gunky water unless it is from a well. I doubt drip systems are flowing at that rate, and I don't see problems with what they are describing.
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Old 08-11-2010, 09:53 AM
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Wet_Boots Wet_Boots is online now
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If you got gunk, then use Maxipaw heads, which function well at lower pressures.

You can avoid the loss of a psi or two by not using any swing pipe connections, but that's a pain unless you run poly pipe.
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Old 08-11-2010, 10:13 AM
BrasiliaFlyer BrasiliaFlyer is offline
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Quote:
Originally Posted by DanaMac View Post
Never heard of that before. But we don't get a lot of gunky water unless it is from a well. I doubt drip systems are flowing at that rate, and I don't see problems with what they are describing.
Good point!
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Old 08-11-2010, 05:49 PM
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txgrassguy txgrassguy is offline
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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.
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Old 08-11-2010, 09:07 PM
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Stuttering Stan Stuttering Stan is offline
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I've never heard of 2 fps requirement. Also, larger lateral pipe not will make a noticeable difference compared to 3/4. Go for the bigger pipe.
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Old 08-11-2010, 09:30 PM
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put in 5-inch pipe, just to be safe
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Old 08-11-2010, 09:36 PM
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irritation irritation is offline
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Quote:
Originally Posted by Wet_Boots View Post
put in 5-inch pipe, just to be safe
5" ?
We use 6". A lot less friction loss but it does take longer to blow out.
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Old 08-12-2010, 01:39 AM
BrasiliaFlyer BrasiliaFlyer is offline
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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.
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Old 08-12-2010, 05:06 AM
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Go 1" everywhere. The guy who ends up servicing it 10 yrs from now will not hate you for it.
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