Design Help

Hi, I'm designig a Sprinkler system that fits a low pressure water system. My water pipe before my meter is 1 inch after the meter it's 1/2 inch. Now I want to design my system with a 1 inch main line and 1 1/4 inch lateral lines(Cheaper, and Complies with City Municipal Code). According to irrigation websites 1 1/4 inch poly pipe should give me 32 GPM and I plan on installing 12 sprinkler heads most of them running at 1.89 GPM. Can this be done and will it run effectively extra GPM is no problem to me this is just an estimate.

An 1 1/4" line may supply 32 gpm if the line is short. Your restriction will be the 1" inch meter and 1" if the line to your house is short most of your restriction will be in the meter.

Plan on you have about 10pgm. You should be able to have 5-6 sprinlkers per station. Make sure you increase the size of the water line coming from you meter to 1" or 1 1/4" and you should be fine.

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Originally Posted by IceTreay

Hi, I'm designig a Sprinkler system that fits a low pressure water system. My water pipe before my meter is 1 inch after the meter it's 1/2 inch. Now I want to design my system with a 1 inch main line and 1 1/4 inch lateral lines(Cheaper, and Complies with City Municipal Code). According to irrigation websites 1 1/4 inch poly pipe should give me 32 GPM and I plan on installing 12 sprinkler heads most of them running at 1.89 GPM. Can this be done and will it run effectively extra GPM is no problem to me this is just an estimate.

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I don't think the system can work as you have described it.

Since you are the "designer" of the system, YOU are responsible for determining requirements and the capability of the source.

Design consists of developing a concept, and then analyzing the design concept to see if it will work. If it doesn't work, you need to change something about the design.

What is total GPM for the maximum-flow irrigation zone? 12 heads at 1.89 GPM per head is about 22.68 GPM.

What pressure do you need for the heads? Your main and laterals will have some pressure loss. Add that to the head pressure requirements.

NOTE: What is the rationale for putting 1 1/4" laterals on a 1" main? Seems bass-ackward.

Now, MEASURE the pressure that can be delivered to the main line through the meter and the line feeding the MAIN from the meter while MEASURING the maximum flow demand.

Based on what you have told us (1/2" line on the output side of the meter; 12 heads at 1.89 GPM per head; low pressure water system) the chance that you will be able to deliver the required flow is somewhere between slim and none.

IF your tests show that the supply won't deliver the flow and pressure that you need, then you must increase the supply or reduce the demand by reducing the number or flow rate of the sprinkler heads. That is called "iterating the design". After you come up with a new design, you analyze that new design to see if it will work.

You say this is only for an estimate. The fact that is is "just an estimate" will not mean much if you build it and all of the sprinkler heads just dribble out onto the grass.

Have you discussed your project with your local irrigation supply houses? The ones in my area have design experts that will design your system to work properly with the given limitations of water supply, pressure, and other factors. And, it's a free service with the understanding that you will buy all of your pipe and supplies from them. This may be just a local thing, but it would be worth looking into.

The limiting factors are that 1" pipe , which will probalby provide 25+ GPM, and the METER itself. You said you had one inch pipe, but is the meter actually a 1" meter? May not be, as most places charge install and base fees based on meter size, and a 3/4 or even 5/8 meter is more common. This would limit you to much less than 20 gpm

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Originally Posted by IceTreay

My water pipe before my meter is 1 inch after the meter it's 1/2 inch. . . .

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The 1/2" pipe is the limiting factor, unless you go all the way back to the meter with bigger pipe.

The OP needs to supply more info. What's the location? Where is the meter located? What is the pressure at the meter? How large a property?

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Originally Posted by Bob NH

The 1/2" pipe is the limiting factor, unless you go all the way back to the meter with bigger pipe.

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I might be misreading; but I thought he meant he would start right at the meter, not using any of the 1/2 to feed the sprinklers. Naturally, if any part of it came through 1/2" pipe, that would be very limiting.

Most water suppliers will require an expensive "Back Flow Preventer" before the sprinkler system.

The 1/2" meter and the 1" line before everything is the next problem.

I suggest you go to your local irrigation supply house for assistance. You may search http://www.johndeerelandscapes.com for a supplier in you area. These people will assist you with the proper design. I don't recommend that you go to Lowes or Home Depot as they don't usually have qualified designers.