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Thread: Polyethylene sizing for general watering needs

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    DIY Member JAR8832's Avatar
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    Default Polyethylene sizing for general watering needs

    Next spring I would like to bury about 220 ft of PE in the yard for general watering needs. This will replace an equal length of garden hose that has to be removed everytime the lawn is cut. The line starts flat, then goes downhill, with the outlet being about 10 feet lower than the source. The house plumbing is 3/4" copper.

    My objective is to have a flow rate at least comparable to the existing garden hose setup. Will 3/4" PE fit the bill? Or would the barb fittings constrict the flow enough to make it worth using 1" PE instead?
    Last edited by JAR8832; 11-23-2011 at 08:25 AM.

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    Forum Admin, Expert Plumber Terry's Avatar
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    220 feet is a lot of friction loss.
    If you have a few sprinklers then 3/4" may not be bad, however if it's upsized, then you would have the option of putting in irrigation with controls.
    For an example.
    A home with 250 feet of 3/4" line, too little volume to run a six head system opening at the same time.
    By changing the line to 1.5", easily produces watering all the way to the end with that many heads.
    It's the same ditch and the same labor. Running PE, you may want to think about 1-1/4" if you go that route. 1" at the minimum.

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    Moderator & Master Plumber hj's Avatar
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    You have to specify if your PE is ips or cts. Cts plastic, of any kind is about the same size as 1/2" copper, as far as the water is concerned. In any case, the size of the pipe depends on HOW many heads are connected and the flow rate needed for them. Usually irrigation systems are run with 1" to the control valves and then either 1" or 3/4" after the valve to the heads, with the final connections being 1/2". You are probably NOT going to connect the new line to the hose faucet, so you MUST have a "pressure backflow preventer", at a minimum, at the connection to the house system.
    Licensed residential and commercial plumber

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    DIY Member JAR8832's Avatar
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    Thanks for the replies. I need to clarify that this isn't for a formal irrigation system, but rather something that will have only a single sprinkler or nozzle operating at a time. I'm trying to replicate the output that a single garden hose would provide. We're on a deep well and irrigation is out of the question. I guess I'll have to start comparing the ID of the different components to see what will be necessary.
    Last edited by JAR8832; 11-23-2011 at 05:07 PM.

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    Moderator & Master Plumber hj's Avatar
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    A "minor" restriction, such as an insert fitting, has little effect on the final volume because the flow's velocity will increase through that small distance to compensate. It is when the restriction occurs over a "long" distance, such as an undersized pipe, that it becomes a major factor.
    Licensed residential and commercial plumber

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