# Calculating GPM on a well



## SCGrassMan (Dec 17, 2017)

Is there a better method / more accurate than just filling a bucket and timing it?

Putting in a system for a well, and it's piped with 1" PVC at the moment. Going to go 1" to the valves, and then 1" Pex line to the individual heads.

I'm going to be running 8-10 MP Rotators per zone. It's a 1/2 HP well pump that pushes a consistent 40 PSI.

Does that sound like it will be able to push all 8 or 10 heads or will I need to chop it into two zones?

And is 1" PEX overkill? 3/4" seems like it would be plenty.


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## Pete1313 (May 3, 2017)

What is the static water level of the well? A 1/2 hp pump may not be enough. I have a static level 120 ft down and although I have a 30 gpm recovery, it took a 1.5 hp pump to pull 16 gpm from the well. By constant 40 psi I'm assuming it is not a cycling system and is a constant pressure system?


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## SCGrassMan (Dec 17, 2017)

It runs until it hits 40 PSI and then shuts off. It's not my well, and sadly nobody knows anything about it. If it's not written on the outside or readable by a gauge I won't be able to answer.


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## Pete1313 (May 3, 2017)

Sounds like a cycling setup. By the plumbing and pressure tank there should be a pressure gauge and a pressure switch. I'm hoping it is set up for 40/60 and not 20/40(pressure the pump cycles on and off). It's important that you design the irrigation flow rate to match the output of the pump. You want the flow to be enough so the pump stays on and does not cycle or you will shorten the pumps life. You can open faucets until you watch the pressure gauge stay constant and the pump doesnt cycle. Then measure and calculate the gpm coming out of your faucets. That is what you should design the irrigation output to be. An easier option would be to get in touch with a well guy and upgrade to a constant pressure system like I did here.

https://thelawnforum.com/viewtopic.php?f=27&t=436#p8125


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## SCGrassMan (Dec 17, 2017)

It's 40/60


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## SCGrassMan (Dec 17, 2017)

We are putting in irrigation and sod - I think their budget is maxed out. The good news is the well is just for the irrigation.


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## Pete1313 (May 3, 2017)

Gotcha. Match the irrigation design to the output of the pump as mentioned above, maybe slightly less and you will be good to go.


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## SCGrassMan (Dec 17, 2017)

I hadn't thought about too low of a flow, I was worried about too much demand to feed all of the heads.

Guess I need to break out the 5 gallon bucket!


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## SCGrassMan (Dec 17, 2017)




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## SCGrassMan (Dec 17, 2017)

Just measured 6 GPM at 30 PSI using the irrigation tutorial for the dynamic flow rating.

So I guess I'm chopping everything up into multiple zones or putting in a bigger pump?


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## SCGrassMan (Dec 17, 2017)

One of my guys caught on that it's rated for 230V but it's wired as 115V single phase.

Might be able to double the output just by running a dedicated 230V line.


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## g-man (Jun 15, 2017)

It is rated for 115/230V. It then has amps at 13.4 and 6.7 for each voltage. This yields the same wattage, 1,541watts. The pump will pump the same. You will have less heat and resistance in the wire by using 230v.

Are they using this pump? Does the welll keep up? What is the well recharge time? Using a low gpm as your design input might be best if you can't answer these questions. Irrigationtutorials explains the well design items to consider.


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## Greendoc (Mar 24, 2018)

Well said. Reviewing the pump model, that looks like a shallow well jet pump. That type of pump is not made to provide pressure. The GT15 or GT20 pumps made by the same company are specifically designed for irrigation service.


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## SCGrassMan (Dec 17, 2017)

Supposedly it's double the HP at 230, but a larger pump will need 230V either way. So my logic was let's get it running on what it's supposed to be.

How restrictive is 6 GPM with rotators? It looks like I can run 6-10 heads off it.

The well is only for irrigation, it's not used for household water.


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## SCGrassMan (Dec 17, 2017)

Greendoc said:


> Well said. Reviewing the pump model, that looks like a shallow well jet pump. That type of pump is not made to provide pressure. The GT15 or GT20 pumps made by the same company are specifically designed for irrigation service.


Yeah I saw that on their website - I believe the GT 20 is what I would want on a 230V line.


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## Greendoc (Mar 24, 2018)

Even a GT 15 would work based on the gallonage you are planning to run. Big pumps are needed to run single stream rotors.


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## SCGrassMan (Dec 17, 2017)

Greendoc said:


> Even a GT 15 would work based on the gallonage you are planning to run. Big pumps are needed to run single stream rotors.


My other issue is the well side input is 1.25" and the output side is 1". Some of the bigger pumps are 1.5/1.5. Once that pipe disappears into the ground on the well side I have no idea what's going on. So I don't know if I can just step down to 1.25" etc.

On the system side how do you feel about 3/4" PEX versus 1" PVC?


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## Greendoc (Mar 24, 2018)

I do not like 3/4 for anything other than to feed drip irrigation. Friction losses in 3/4" will cause problems. Especially if your pressure is limited. I do not see that kind of problem in the systems I deal with as long as the gallonage of the water meter is not exceeded and incoming pressure is 80 PSI. If pressure is lower than that, 1" and larger becomes a good idea.


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## SCGrassMan (Dec 17, 2017)

I think 1" is the way to go then. Can I do 1" PEX?


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## SCGrassMan (Dec 17, 2017)

@Greendoc something like this:

https://www.lowes.com/pd/SharkBite-1-in-x-300-ft-PEX-Pipe/1000391339

Flexible pipe would help me out in a variety of ways on this project


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## Greendoc (Mar 24, 2018)

1" PEX is more like 3/4" PVC SCH 40 in terms of flow. Good choice. 3/4" PEX would be more like 1/2"


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## SCGrassMan (Dec 17, 2017)

Greendoc said:


> 1" PEX is more like 3/4" PVC SCH 40 in terms of flow. Good choice. 3/4" PEX would be more like 1/2"


Ok, thanks. I mean 1" schedule 40 is certainly an option. I could do the irrigation heads on schedule 40 and just feed the zone with pex so I can curve things easier.


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## g-man (Jun 15, 2017)

I'm not sure why use PEX. It is an overkill in irrigation. 125psi Poly pipe would be fine. 1in PEX = ~3/4 copper.


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## J_nick (Jan 28, 2017)

I used 1" class 200 for my zones. Then came off it with 1/2" swing joints. It has quite a bit of flex to it but not near as much as PEX would have.


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## g-man (Jun 15, 2017)

Also, PEX cannot be exposed to sunlight. UV breaks it down.


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## SCGrassMan (Dec 17, 2017)

J_nick said:


> I used 1" class 200 for my zones. Then came off it with 1/2" swing joints. It has quite a bit of flex to it but not near as much as PEX would have.


Class 200 is what I'm replacing. Shattered pipes all over the place. I have no idea, other than saving a very few dollars, why anybody would use that stuff. Super thin walls.


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## SCGrassMan (Dec 17, 2017)

g-man said:


> Also, PEX cannot be exposed to sunlight. UV breaks it down.


I plan on burying it  Could be poly instead of PEX. Just 1" and flexible is the important part.


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## J_nick (Jan 28, 2017)

I guess I'm just an idiot :crazy:


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## SCGrassMan (Dec 17, 2017)

J_nick said:


> I guess I'm just an idiot :crazy:


Nah that's not what I mean lol. You gotta understand we've spent 4 days digging all of this crap up from under bushes and tree roots etc. I don't ever want to dig it up again. So it's schedule 40 or poly pipe for me.

I plan on putting a fitting for blowing it out every fall but that definitely didn't happen before and I think the pipes froze.


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## J_nick (Jan 28, 2017)

SCGrassMan said:


> .... I think the pipes froze.


I think that's probably what happen also. Especially since you have multiple places where the PVC broke. Class 200 is meant to be irrigation pipe after all. The "class" designation is for the PIP system, Plastic Irrigation Pipe. But like all plastics they will get brittle with age and break.

Why dig the lines up? I would have just left them in the ground and trenched new lines where I wanted. Pick up the pieces that came up from the trencher, throw them away and be done with it.


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## SCGrassMan (Dec 17, 2017)

Well, we needed to find valves and heads and some other things. We were hoping we would be able to fix what was there. We ultimately only dug up about half, before we realized it was gonna be a complete redo.

We used people and not a trencher 

I did use a sod cutter though for removing the sod.


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