# Rainbird design… does it really need to be this involved?



## Majahops (Sep 26, 2021)

Hey guys. I have 3/4 PEX water supply. I'm going to bring it out of my basement into my front yard. All other things being equal, what would you think would be better to serve an irrigation system that is primarily but not exclusively for lawn sprinklers: 3/4 PEX or 2 in PVC?

Thanks so very much ahead of time!


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## ricwilli (Feb 18, 2019)

I ran 1 inch pvc pipe for my irrigation. That should be enough depending on how many heads per zone.


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## Majahops (Sep 26, 2021)

ricwilli said:


> I ran 1 inch pvc pipe for my irrigation. That should be enough depending on how many heads per zone.


Don't get me wrong I do so very much appreciate your response, but I'm sort of wondering between 3/4" PEX and 2" PVC, which would be preferable/optimal in an "overall" sense?

Thanks so much again.


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## bernstem (Jan 16, 2018)

Pipe size depends on expected flow rate. Larger pipe has higher maximum flow. 
3/4 PEX has a max of 4.6-6.4 GPM depending on inside diameter. This would be used for a funny pipe run
2 inch schedule40 PVC has a max of ~55 GPM. This was be used for a large irrigation zone or in a golf course.

I don't know that there is any need for 2 inch PVC in a home irrigation system. Most home water supplies are limited to 12-20GPM. You would be better off with 1-1.25 inch PVC for the main line which has max GPM of ~15-20.


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## Majahops (Sep 26, 2021)

bernstem said:


> Pipe size depends on expected flow rate. Larger pipe has higher maximum flow.
> 3/4 PEX has a max of 4.6-6.4 GPM depending on inside diameter. This would be used for a funny pipe run
> 2 inch schedule40 PVC has a max of ~55 GPM. This was be used for a large irrigation zone or in a golf course.
> 
> I don't know that there is any need for 2 inch PVC in a home irrigation system. Most home water supplies are limited to 12-20GPM. You would be better off with 1-1.25 inch PVC for the main line which has max GPM of ~15-20.


Very helpful. Thank you greatly.


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## Majahops (Sep 26, 2021)

bernstem said:


> Pipe size depends on expected flow rate. Larger pipe has higher maximum flow.
> 3/4 PEX has a max of 4.6-6.4 GPM depending on inside diameter. This would be used for a funny pipe run
> 2 inch schedule40 PVC has a max of ~55 GPM. This was be used for a large irrigation zone or in a golf course.
> 
> I don't know that there is any need for 2 inch PVC in a home irrigation system. Most home water supplies are limited to 12-20GPM. You would be better off with 1-1.25 inch PVC for the main line which has max GPM of ~15-20.


Sorry, last thing, PVC won't be an issue in the Northeast?

Thanks again!


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## bernstem (Jan 16, 2018)

I don't think PVC will be an issue, but I am not an irrigation expert.


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## Colinwjholding (Apr 6, 2020)

If you have the option of both i would 100% take the 2" pvc feed and then just reduce it to 1.25" for your mainline. then run 1" for your zone lines.

This way guarantees you max gpm flowing from the valves.

Depending how much you have to irrigate you could even go bigger.

PVC 100% not an issue in the PNW. It is all i use for my installs.


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## Majahops (Sep 26, 2021)

Hey Guys I realize there are pressure boosters. Are there primary flow boosters as well? Anybody know if any? I'm good on pressure but could use a few more Gpm. I'd be willing to spend a couple hundred dollars. Thanks so very much.


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## bernstem (Jan 16, 2018)

Your flow is likely limited by the house supply line and water meter. Upgrading them is the best way to increase overall flow. If you are lucky, you have a small water meter and large supply line. Upgrading the water meter if it is the limiting factor will net you at least 3-5 GPM and should only cost a couple hundred dollars at most. Upgrading the house water line will be much more expensive.


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## Colinwjholding (Apr 6, 2020)

The gpm is dictated by the size of the pipe. For example a 3/4 line flows 9gpm
1" 16 gpm
1.25" 25gpm
1.5" 35 gpm
2" 55 gpm.

My system goes from 3/4" from my meter at 120 psi , upsized to 1.5" and after 600ft still sits at 85 psi.


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## Majahops (Sep 26, 2021)

bernstem said:


> Your flow is likely limited by the house supply line and water meter. Upgrading them is the best way to increase overall flow. If you are lucky, you have a small water meter and large supply line. Upgrading the water meter if it is the limiting factor will net you at least 3-5 GPM and should only cost a couple hundred dollars at most. Upgrading the house water line will be much more expensive.


My mainline is 3/4 and my meter is 5/8". Believe me upgrading my meter was what I had hoped to do… but My water authority says they have a huge backlog for water meter installs due to COVID and supply issues. Am I able to buy and install a meter from a third party and install it myself?


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## bernstem (Jan 16, 2018)

Majahops said:


> bernstem said:
> 
> 
> > Your flow is likely limited by the house supply line and water meter. Upgrading them is the best way to increase overall flow. If you are lucky, you have a small water meter and large supply line. Upgrading the water meter if it is the limiting factor will net you at least 3-5 GPM and should only cost a couple hundred dollars at most. Upgrading the house water line will be much more expensive.
> ...


The water company won't let you install your own meter. It needs to be supplied by them as they interface with their system. In fact, it is probably illegal for you to change without their permission. A 3/4 copper line with 5/8 inch meter should flow 20 GPM. If you are seeing less than that, look for a restriction somewhere else. 20 GPM is usually more than enough for a residential irrigation system - especially on 4k square feet.

What is the problem you are trying to address with more flow?


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## Majahops (Sep 26, 2021)

Thanks so much for taking the time.

I'm actually getting 10 Gpm, which is what the water authority guy says is par for the course. 



bernstem said:


> Majahops said:
> 
> 
> > bernstem said:
> ...


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## bernstem (Jan 16, 2018)

Wow, 10 GPM from a 3/4 inch supply and water meter seems low. It might be that the main line tap is small, but the water company would have to tell you what size that is. I'm assuming the 3/4 inch line is copper, but if it is galvanized it may be old and be restricting flow.


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## g-man (Jun 15, 2017)

I merged this topic @Majahops @bernstem with a previous conversation from the same author and similar subject.

I have 3/4 PEX too at my home and I kept my design gpm to no more than 6gpm.


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## Majahops (Sep 26, 2021)

That's awesome and encouraging! So that means 6 Gpm total per set of concurrently running zones? And sorry for creating a new thread for essentially a very similar topic appreciate your merging them.



g-man said:


> I merged this topic @Majahops @bernstem with a previous conversation from the same author and similar subject.
> 
> I have 3/4 PEX too at my home and I kept my design gpm to no more than 6gpm.


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## g-man (Jun 15, 2017)

No more than 6gpm per zone. I only run one zone at a time. This gives some wiggle room for the peak of summer and the water pressure drops we get. I used 1in PVC for the main, 1in poly 125psi rated for the main branch and 3/4in poly for the laterals. Lower gpm also help with lower friction pressure losses.


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## Majahops (Sep 26, 2021)

That's very helpful! Thanks so much man!


g-man said:


> No more than 6gpm per zone. I only run one zone at a time. This gives some wiggle room for the peak of summer and the water pressure drops we get. I used 1in PVC for the main, 1in poly 125psi rated for the main branch and 3/4in poly for the laterals. Lower gpm also help with lower friction pressure losses.


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## bernstem (Jan 16, 2018)

It is probably worth noting a few things about water flow in irrigation piping. You can push flow rates very high with enough pressure, but you start to run into problems with bursting, excessive wear, and noise. In general, water pipes have a maximum "safe" velocity of ~5 ft/sec. The max flow rate is relatively constant for most home pipe sizes.

When you consider that max flow rate is constant for irrigation pipe across all common diameters then maximum flow volume (GPM) will increase with increasing pipe diameter. That is where the GPM recommendations for pipes come from. As expected 1/2-inch pipe will have less flow than 1 inch pipe at 5 ft/sec (~3 vs ~12 GPM). If you push flow higher (12 ft/s) then you can get flow volumes of ~7 and ~30 GPM. If you keep pushing the flow velocity, then you can push 90+ GPM through 1 inch pipe, but the velocity will be very high (~36 ft/sec).

When designing an irrigation system, you have to have an idea of how much flow your water supply and meter will provide. If you exceed the maximum in the design, the heads will not have enough pressure to function or will not pop up. As long as you are under the maximum (general recommendation would be 20%), you will be fine.

The output also matters. If you have 4 heads at 1 GPM at your pressure, the maximum flow in the main irrigation line will only be 4 GPM, even if it is a 4 inch pipe. When you consider that the max flow requested from the system is limited by the max flow of all heads on a zone, you can see that there is no need for the expense of bigger pipe.

Using your thumb on a garden hose demonstrates flow rate and diameter quite well. With the garden hose on the water flow velocity is enough to push the stream a few feet or so with the end open. Decrease the diameter with your thumb and you can increase velocity enough to throw the water 20+ feet. This happens because flow volume remains almost the same whether the hose is open or your finger is over the end.


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## Majahops (Sep 26, 2021)

That was a super cool lesson. I appreciate it very much!



bernstem said:


> It is probably worth noting a few things about water flow in irrigation piping. You can push flow rates very high with enough pressure, but you start to run into problems with bursting, excessive wear, and noise. In general, water pipes have a maximum "safe" velocity of ~5 ft/sec. The max flow rate is relatively constant for most home pipe sizes.
> 
> When you consider that max flow rate is constant for irrigation pipe across all common diameters then maximum flow volume (GPM) will increase with increasing pipe diameter. That is where the GPM recommendations for pipes come from. As expected 1/2-inch pipe will have less flow than 1 inch pipe at 5 ft/sec (~3 vs ~12 GPM). If you push flow higher (12 ft/s) then you can get flow volumes of ~7 and ~30 GPM. If you keep pushing the flow velocity, then you can push 90+ GPM through 1 inch pipe, but the velocity will be very high (~36 ft/sec).
> 
> ...


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## Majahops (Sep 26, 2021)

Hey guys, I need an irrigation system to keep my grass from going dormant for the six hottest weeks of summer, and to keep grass from drying out when overseeding. My yard is super sloped and unevenly so based on the slope of the street I live on. I planned on maybe 6 sprinklers for each side of my lawn… but what rainbird sent me is clearly designed for perfection. I don't need perfection, I just need to keep grass watered enough to keep it from dying, without having to continuously run out to move sprinklers. Can anyone think of a way I can reasonably have just like 6 sprinklers on each side rather than this very intricate system? For complicated reasons, I'll be digging the trenches myself - at a rate of maybe 1-2 per week (I did the first one today, it took me several hours). Thanks so very much.


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## thebmrust (Jun 29, 2020)

We have pressurized irrigation at 60psi. I have 1.25 in main lines and 3/4in risers.

3/4 house supply to 2in yard line doesn't seem very efficient.


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## Majahops (Sep 26, 2021)

Wanna trade houses?


thebmrust said:


> We have pressurized irrigation at 60psi. I have 1.25 in main lines and 3/4in risers.
> 
> 3/4 house supply to 2in yard line doesn't seem very efficient.


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