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Phil
Phil, Mechanical Engineer.
Category: Plumbing
Satisfied Customers: 7585
Experience:  Retired mech. contractor, shop owner, 51 yrs experience.
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I need an expert on yard irrigation, iam on city water with

Customer Question

I need an expert on yard irrigation, iam on city water with a ,separate from house, 1" meter, with a min of 50psi and 30gpm. I was planning on using Hunter MP 3000 90 *- 210* rotary heads shooting 30ft. My irrigation store, guy says it will work as long as I loop the supply pipe, using 1.5" CL 200 PVC pipe and loop the zones using 1" CL 200. Hunter says the optimal psi for these heads 40psi. I'am using a tutorial on line with spreadsheets for this and other pipe. Stick in the numbers gets psi loss. If the back flow preventer loss is 6psi, valve is 5psi, iam below 40psi right there. I know that looping, when u put your numbers in u divide your gpm , and feet of pipe in half . I get 1.83psi loss for the supply pipe and 4.62 psi loss for the longest zone . This uses an error factor of 1.1 for couplers and bends in the pipe. I don't understand?
Submitted: 1 year ago.
Category: Plumbing
Customer: replied 1 year ago.
It's been about 24hrs, no answer yet?
Expert:  Phil replied 1 year ago.
Welcome!
We are apparently short on irrigation specialists here. The issue however is not so much an irrigation issue as a mechanical engineering issue.
Simple pressure loss calculations, most of which you have already done.
Having designed industrial piping systems over a span of 51 years it seems that you are over thinking this situation, all of these sorts of things operate within *broad tolerances*, worst case here might be a 25 foot throw from the sprinkler head instead of the rated 30 foot throw.
'Broad tolerances' are the over riding key words here.
You are looking at a bit less throw from the sprinkler heads if the water pressure at the sprinkler head is lower than the sprinklers ideal or peak rating.
The reduction in throw would be in direct proportion to the loss of head pressure within limits (say a 20% drop in pressure, would reduce the sprinkler head throw by 20%)
Obviously if you dropped the head pressure to say 5 psig for example there would not be enough pressure to rotate the sprinkler... but we are not talking about much of a head pressure loss... you also have the option of increasing the pipe size to the longest zone to 1-1/4" and reducing that pressure loss by 70 or 80%
The other aspect is that city water generally runs higher than 50 psig you can simply fit a pressure regulator and set it higher to offset the pressure losses in the valves and piping,
Let me know what you think, we can go from there.
.
Customer: replied 1 year ago.
I wrote a reply yesterday, with some more questions, not sure if u got it?
Expert:  Phil replied 1 year ago.
Hello again, I did not get the questions, Can you repost them to this dialog by pressing the 'reply' button.
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Customer: replied 1 year ago.
Ok , I wish I'd wrote them down. We have right out of the meter 50psi and 30gpm, only when the city's pump is on do we have 68psi. It's a random thing, water tower gets low, pump comes on. Usually runs in the afternoon, so we can't count on it. I put a gage right behind the meter, and timed how long to fill 5gal bucket, run it 5, 6 , times at different times , and days. IAm sure iam overthinking it, but iam not putting pipes in the ground without knowing for sure , there right . If they tell me I can exchange the MP-3000 for a reg robor , I might try them. My math is telling me he' s wrong. Jess Strykers tutorial , his golden rule is never space heads further than u have pressure, 30ft, u better have 30psi or more. So I've pretty much decided to go with reg rotors , there's a lot more flexibility, with the different nozzles. The idea pressure for them is still 40 psi, some 45, but u can get down to 30 and make them work, for the 30ft that I want them to throw, and the spec say they can throw more. But the spec are recorded inside a building , so there's no wind, which is another reason to have more flexibility. Unles iam doing it wrong, I barely have 30 psi, even looping both the supply and the zones ,which is a lot of extra pipe. I can ditch the filter, and lose 5psi of loss, we live in a pretty sandy area, so I thought it was a good idea, but I don't know anyone that runs I filter, so it's probably ok to not use it. One question I have is if u have 30gpm , can u use it all, as in if u want to use 3 gpm nozzles, can u run 10 heads in a zone?
Another question if u have small, length of pipe off the looped supply pipe, do u figure it's friction loss using the looped way or because it dead heads , do u figure it the reg way? But the main question, is am I figuring it right, why are they telling me it will work, when I can't get it to work past the backflow preventer , and filter, and a valve, which is 16psi minimum . Thanks Kevin
Expert:  Phil replied 1 year ago.
Hello again,
Regarding the looped supply, don't look at it as a 'dead head issue' but as a single pressurized loop. The loop will cut your pressure drop calculation for a single supply line in half, and provide equal pressure to all sprinklers... its much better engineering.
You will get a lot less than 16 psig pressure drop, if the back flow preventer is 6 psig, and you use a full port ball valve for shut off that will be 0 psig loss, and loop the supply that will be .9 psig, and size the supply to the furthest sprinkler in order to get 1 psig pressure to it at 3 gpm (0.9 psig) as you do to the rest of the sprinklers.
Thats 8 psig total loss to each sprinkler head, or 42 psig when the city water pressure is at 50 psig.
You can run 10ea, 3 GPM heads in a zone.
....
We are on the honor system here. Please remember to rate my service before you leave today. If you need anything else, just let me know. You can continue asking follow-up questions at no additional charge.
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Customer: replied 1 year ago.
I don't know what a full port valve is, I'am talking about the electric zone valves 1" . The supply is 632ft and I get the loss as 1.69psi with 1.5inch cl200 PVC . The longest zone is 484ft , also 1.5" cl 200 , with 1.29psi loss both are looped . Really going any bigger , won't be cost effective or practical , trench wise etc. but the irrigation co man had the zones using 1" cl200 which would be close to 8psi loss. U undrstood me about the a small length of pipe off the supply pipe that is still supply pipe it just goes to a valve , like 36ft . the looped way it would be .1psi loss and .69psi loss the reg way? Is the reSon I can use the whole 30gpm, because the pipe is big enough to handle the flow? If it were 1" it couldn't?
Expert:  Phil replied 1 year ago.
Hello again, I probably made a mistake in using your pressure drop numbers without looking them up myself. I need a full specification on the tubing you using.
A full port valve is a valve with the port size the same as the inside diameter of the pipe.
The irrigation type valves are normally diaphragm types and those do need a pressure drop to operate... see if you can find some full port plastic ball valves, you do not need a pressure drop to operate those.
How many sprinklers are on the longest zone.
Looping a zone cuts whatever a single supply pressure drop in half.
.
Customer: replied 1 year ago.
The longest zone is 280ft looped, and in this plan there were 5, in each of 8. I would redo the zones and heads per zone, if I were to use it. The pipe CL 200 PVC ips pipe, pipe coefficient is 150, the 1.5" pipe I'd is 1.7, he uses a error factor of 1.1, this is an adjustment value to account for manufacturing error, fittings, bends, in pipe etc. u can find these at Irrigation Tutorials.com. I've looked for some larger valves, what I found was, the reg valves with flow control ,are around $14, $15 , 1.5" are $50, $60. The valves, your talking about are hundreds each , for electric ones, I'd need 8 or more, way to much.
Expert:  Phil replied 1 year ago.
This is getting into a bit of engineering... well beyond just pipe sizing, you may not need all those valves.
If you can send a photo of a neat pencil sketch of the system that will help. Use the 'attach files' link at the lower left of your reply box.
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Customer: replied 1 year ago.
One shows head placement, 30ft and the other , the zones.
Expert:  Phil replied 1 year ago.
Hello again, thanks for the sketches.
There are several issues here.
1. With just the verbal description of the pipe loops and no drawing of the *pipe there seems to be conflicting loop length numbers. Not enough for me to run reliable calculations on.
2. The other factor is that for any input I provide to be reliable this will take way more time than I can afford, its a small engineering project... does not fit into the miniscule pricing structure here by a wide margin.
I will opt out for the time being, perhaps someone else here will want to take this project for you, most likely on an additional services basis however.
.
Customer: replied 1 year ago.
For this plan the length oh pipe is 685ft for supply pipe, I believe that includes the three pipe Spur coming off the main , to a valve zones. For the zones, only the longest one, giving the max loss is important which is zone 2 an 9 , 8, are the same at 280ft. In this example, the zones use 1" cl200 pipe , that is what my retailer said will work , but I can't get to work. All the zones are laid out laterally except z-3 which makes a circle , the others do to but have to use twice the pipe basically because they run in a line right next to the pipe that the heads are on. The reason for this layout is three utilities on south side ,two on west, 5 on the north , 1 on the east. In order to have as little as possible hand digging over them. On the north, there's just to many , my heads need to be at least 22ft off the property line , mine are at 24ft. On the west and south they cross as little as possible. In past responses I may have given different length, for main loop , i'am working on different layouts, but this is the layouts , that my man said would work . This still goes back to the same basic question of needing a minimum of 40psi for the rotary heads to work, I've got 50psi. If the backflow and a valve are 11psi of loss, how can it work , the loss for everything else could be zero, where already under 40psi? Iam not sure about u saying there no drawling of the pipe, the picture that doesn't show the radius of the heads , shows the pipe. Also not sure about it being a small engineering project? I looked up the loss for the backflow preventer and the valve, which are 11 maybe 12psi loss. So unless there's something iam missing something, it can not work? Going back to gpm, what I was getting at was With any size of pipe only so much , can be pushed through it, 1" has a max number, 1.5" has a max, which I think is 34gpm, so this is why I can use the whole 30gpm? Thank u
Customer: replied 1 year ago.
I think I've stumped just answer?