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Starting Member


Thursday, May 1st 2008, 12:51am

Designing my first system and have a question about my gpm

i have a question on my system that I am desinging. I have been using the Jess Stryker irrigation tutorial on the web and I have gotten as far as setting up the zones and determining how many heads to put on my zones. I have a 1 1/4 mainline coming into my valves and per the tutorial I could use a GPM of 23 becasue of this. However when I checked the flow out of a hose bib I only had 10 GPM. My question is would I be safe using the 23 GPM for my head and zone placement or should I fall back on the 10 GPM to be safe? I am installing a whole new system so I will be buying all new valves. I just don't want to spend more than I have to.

One more thing. Does anyone like a particular in line valve over the others? I was looking at the hunter hpv-100gs but not sure if that is overkill or a good one for a smallish yard. How does the quality stack up to others? Any help would be appreciated.


Supreme Member

Posts: 5,298

Location: Metro NYC


Thursday, May 1st 2008, 7:22am

Check the flow from your actual mainline plumbing, and design to fit.


Supreme Member


Thursday, May 1st 2008, 7:45am

One of the considerations in sizing pipe is that you want to observe the 5 feet per second speed limit. If water is allowed to flow faster than that, you increase risks of water hammer and damage to the plumbing. This is because kinetic energy quadruples as speed doubles.

This 5fps speed limit is where you are getting the number 23GPM for a 1-1/4 Sch40 PVC mainline. If you attempt to force more than 23GPM through a 1-1/4 mainline, you will be violating the 5fps speed-limit.

But just because there is a speed-limit doesn't mean your system can move that fast. As a ridiculous example, if your mainline pipe was 500' long and you had a static pressure of 10psi, there is no way in %#!! you are going to get 23GPM moving through that pipe.

So like Wet_Boots says, you've got to design for what your plumbing can produce, not the maximum allowed by "law".


Saturday, May 3rd 2008, 4:34am

Agree with wetboots. do your bucket test out of the 1 1/4" mainline and youll get your answer.

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