new system design opinion

[jabbo]

If you could design a system from scratch before the well was dug on an acre of centipede what gpm's would you tell your well guy.

[sildoc]

If you could design a system from scratch before the well was dug on an acre of centipede what gpm's would you tell your well guy.
as much as you can afford. I have talked to a well driller before. There is an art to their science, however there is only a certain amount that mother earth is going to give up. That will vary as to where the property is located.
We had a well on the ranch that cost us 48000 in 1985. It average flow is 40000gpm. The guy down the road less than a mile put in a well at the same time. He only gets 300 gpm. He went deeper and only got 100 gpm more and it cost him almost 100000 grand. We have since sold water rights and lease out the property but my point is that it will vary on what you can get and your well driller can tell you oh we can get you x amount of gpm but what is the cost and how deep is he going to have to go?
There are several hundred wells drilled a year that don't even have a 2gpm rating or better.

[bicmudpuppy]

as much as you can afford. I have talked to a well driller before. There is an art to their science, however there is only a certain amount that mother earth is going to give up. That will vary as to where the property is located.
We had a well on the ranch that cost us 48000 in 1985. It average flow is 40000gpm. The guy down the road less than a mile put in a well at the same time. He only gets 300 gpm. He went deeper and only got 100 gpm more and it cost him almost 100000 grand. We have since sold water rights and lease out the property but my point is that it will vary on what you can get and your well driller can tell you oh we can get you x amount of gpm but what is the cost and how deep is he going to have to go?
There are several hundred wells drilled a year that don't even have a 2gpm rating or better.
Very sound advice. Here in my location, within 10 miles, a "good" well might bring 10gpm. Other spots will have less than 5gpm. Many rural homes get placed on cisterns that wells fill almost 24/7 so that the house pump can run 5+gpm to run showers, etc. from the cistern. I have recomended wells to fill ponds in the same fashion so we could irrigate from the pond. Run the fill pump/well for 20+ hours a day so you can pump from the pond for 6............ Hopefully your in better water country than I, but a well expert will be able to give you good advice.

[jabbo]

You really did not answer my question. Lets say that the well guy says that he can put a 4" well in for "x" amount of dollars and I have the option (for that same amount) to have a choice from 10 gpm's to 30 gpm's what would be your choice. We don't have many problems with wells going dry. As a matter of fact we have some wells that are only 40 to 50 feet deep with all the water you want! Again this is for 1 acre of centipede. The reason I am asking is because I already have a 1.5 horse that produces about 13 gpm at 50 psi and I am debating on if I want to spend that much time a week watering because I am not going to be able to put alot of heads on a zone. Also the heads are not going to be able to have that much flow/pressure. So I was thinking before I even start designing this system that in the long run (as far as watering time per week) I would be better off to change out my well pump! Sorry for such a long post.

[sildoc]

You really did not answer my question. Lets say that the well guy says that he can put a 4" well in for "x" amount of dollars and I have the option (for that same amount) to have a choice from 10 gpm's to 30 gpm's what would be your choice. We don't have many problems with wells going dry. As a matter of fact we have some wells that are only 40 to 50 feet deep with all the water you want! Again this is for 1 acre of centipede. The reason I am asking is because I already have a 1.5 horse that produces about 13 gpm at 50 psi and I am debating on if I want to spend that much time a week watering because I am not going to be able to put alot of heads on a zone. Also the heads are not going to be able to have that much flow/pressure. So I was thinking before I even start designing this system that in the long run (as far as watering time per week) I would be better off to change out my well pump! Sorry for such a long post.
I am not even sure you are asking this question. If you can have 30gpm why choose 10? I find that if it is the same price there really is no question of what to do. You will need it later. Any ways a 30gpm well today might be the 10 gpm well in the future and visa versa. Go large work on the pressure thing later.
Now why the larger? Because most likely you are filling a tank also. Your pump only has to work half the time to fill the tank on a higher gpm well where if you have a lower gpm well you are going to have to replace the pump sooner because it is working harder.

[Wet_Boots]

There is no real economic motivation to go changing pumps or drilling wells, if the existing well and pump can supply the existing needs of your lawn. (and yours can do so, if you bother to run the numbers) By all means, if you care to, design a system with ability to use more water (by replacing existing nozzles with larger ones) in the event that you do replace a pump with a more powerful one. Choose larger pipe sizes, and there won't be excessive flow losses when a new pump is put in place.

[Wet_Boots]

If you want to install a larger pump, and your well can supply the water, then nothing is stopping you. It's only money. What you have yet to state is what it is that requires you to obtain more water. You could have less than half your current gallons per minute, and still water an acre. I've had to work with even less than that, and still managed to cover the area. Some more details, please. Is your soil sandy? Extremely sandy soil drinks in much more water than normal soil will. Is there some absolute limitation on the hours that the sprinklers can be running? Pin down some of these variables, and and some informed advice might follow. For now, all you have is some vague feeling that you want more. Who doesn't?

Compared to what you'll get back on sprinkler system savings, a new pump here won't be paying for itself. And you do want to consider the short-cycling of a more powerful pump on your existing pressure tank. A pump puts out X gallons per minute maximum. The pressure tank has a Y gallons minimum drawdown. Run the numbers, and you will obtain Y/X minutes (minimum) between pump starts. - steel pressure tanks can rust out. If your tank may someday give out, adding an additional one, maybe a fiberglass model, will add needed drawdown as well as providing some insurance.

[jabbo]

Ok, I'm going to try and make this as short as possible. First of all, I really appreciate the help and I would really like for you to walk me thru this so that I can decide what I need to do. I have a little over an acre of really sandy land with centipede on it. I have about 13 gpm @ 50 psi as far as I can figure. I want to use mainly hunter stuff and have been doing some figuring using one of there books. As far as I can tell with that flow I can put about 4 or 5 pgp's per zone using #5 nozzle for 2 gpm. If I use head to head spacing I am going to have to space them about 30 ft. apart. I sat down and kinda drew out some heads and spaced them out for 30 ft. I came up with around 80 heads( I know some of this "figuring" is probably wrong so that is why I am asking all of the questions). With that many heads I am going to have around 15 or 16 zones plus the flower beds. Going by the manual a #5 nozzle will produce about .15 tenths in an hour for a full circle. At that rate it will take me running my system all night long all week long just to water over the yard one time. Then I'll have to start all over again. And like I said please correct any of this if it is wrong. So I was thinking about the long term $ amount and was going to icrease my flow so that I had about twice as much flow so I could space the heads out further and put out more water at the same time. It would be a cost increase at first but after that I would not have to run my system near as long to cover the yard. I'm trying to think about 10 or 15 years down the road. I need all the advise I can get so if you think I don't need to change out my pump and will not have to spend all night watering then shoot me some numbers or scenarios. Sorry for the long post.

[williamslawn]

We like to have 30GPM so we can use 8 heads a zone with 3.0 nozzles. I set my pumps to run constantly while irrigation is on. But as someone else said if you can only get 13 GPM then you will need to design your system on the amount of water you have.

[jabbo]

Thanks for the reply. I also did some "figuring" after I decide to go to 30 gpm's and found that I could even use 4 or 5 heads still but would be putting down more than three times the water and also could space the heads at like 45' instead of 30'.

[Ground Master]

30 gpm for an acre

[Wet_Boots]

I already have a 1.5 horse that produces about 13 gpm at 50 psi 30 gpm is a bit of a reach. Expect closer to 25 gpm if you install a 3 horsepower pump. You don't need more to cover an acre, even if it's sandy. To evenly cover an acre with one inch of water takes about 27000 gallons. At 13 gallons per minute, that works out to about 35 hours of pumping. Per Week (sometimes the calculations miss that detail) - So, as a starting point, you're pumping 35 hours a week to put an inch of water on an acre. Add the detail of extremely sandy soil, and you could double that amount of water, and get 70 hours a week. But you will not reach the point where all-watering all-the-time will not be enough to nourish that thirsty acre. A larger pump would be nice to have, but absolutely necessary? No.

With 50 psi, you could create a layout for an acre that uses less than sixty heads. Less than fifty, probably. Not counting mist heads in beds.

[bicmudpuppy]

One acre? 200x200=40,000'sq. 210x210 would be an 8x8 grid w/ 30'spacing and mean 64 heads 4 of which are 90degree heads and 24 of which are half circle heads. So 28 heads with the equivalent of 13 full circle heads and 36 true full circle heads means the equivalent of 49 heads @ 4 gpm each or 196gpm. 196/13=a fraction over 15 zones. So 16 zones of rotors even at 2 hours per zone means 4 days for 8 hours per day. Centipede, even in sandy soil is going to thrive on that. Personally, I would stretch things slightly and grid 7x7 or 49 heads. So only the equivalent of 36 full circle heads. Now we are down to 12 zones and watering for 2 hours every 3 days for 8 hours per day. So, I'm with wetboots, asking why do you need to spend thousands of dollars on a new pump?

[jabbo]

Thanks. It would be very good news to know that I didn't have to change out that pump!! I just didn't want to design it and crank it up and have a few heads per zone just peeing out about 25' or so. So can you give me a configuration as far as number of heads per zone,how many zones, gpm of head or pgp nozzle, the amount of time each zone will run, size of mainlines and laterals etc... I have run the numbers using 13 gpm many times and also I'm not trying to be totally helpless here I just want some good sound advise from someone that installs these heads/valves everyday and knows exactly what they will do. I have never even seen a pgp except in the books!! Also back to the question about the pump start relay and cycle stop valve. Do you guys think that I will need either? Another thing (which I hope is a good thing) is that I have a good bit of elevation change in my favor because my well just happens to be sitting on the highest place in my yard, even higher than my house!!! But I have yet to measure it exactly.

[bicmudpuppy]

You stated a running pressure of 50psi @ 13gpm. Design for 12-14 gpm per zone and set the pressure switch so it doesn't kick off when a 12 gpm zone is running and you should be fine. You may have 55 or 60 psi at 12gpm, but that isn't a big deal. Set up this way, you don't need a pump start or cycle stop. What type of backflow are you required? With a RPZ, your going to lose probably 20psi in the piping. With a Double check, less than 15 psi. Nozzles should be selected so that a full circle head is 100%, 3/4 or 270 heads are 75%, 1/2 or 180 are 50%, 1/4 or 90's are 25%. Your corners are going to be a little bit short if you use PGP's and figure 100% is 4gpm, but that is how I would lay it out. Again, I'm banging my irritrol drum, but I like the CR500 because the 1gpm @30psi nozzle will throw 28'. So you use #4's for fulls, and #1's for corners. Some guys here are saying the RB 5004's work just as well. I haven't tried them. For PGP nozzle set, I would recomend a 3,6,9 nozzle set w/ the #8 if you had to go 3/4's. The 9's are just over 4gpm @30psi but you should be OK. 3 heads per zone on the fulls. Try to include six half circles w/ each corner. Is the lot square? Does the 7x7=49 rotors layout work? If so, you have a total of 24 perimiter heads. If you make 4 zones of `1 corner head and 5 half circle heads, you will have 4 zones @ 11gpm each. We now have 4 half circle heads on the perimiter left to zone w/ 25 full circle heads. So a total of 9 zones @ 12gpm (actually 12.6) each. This means 13 zones total, and the precip rate on #9 nozzles square spaced w/ 30psi head pressure is .56" per hour. So they can run once every three days and exceed 1"/week.

[bicmudpuppy]

On a side note to go with my above post, this would lay out much cleaner, if you put all four half circle perimiter nozzles on one zone w/ one extra full cirlce head, and then ran the other 24 fulls as #6 nozzles for twice the run and half the zones. This means 6 heads per zone and only 4 zones instead of 8. These zones would need to run twice as long, but it is the same total run time.
1 1 1 1 1 4 4
5 5 9 9 9 9 4
5 8 8 8 9 9 4
5 8 8 8 7 7 4
5 7 7 7 7 6 3
2 6 6 6 6 6 3
2 2 2 2 3 3 3


OK, the table didn't paste like a table, but if it holds format, you will get the idea. That is a 7x7 and each number represents a zone.

[Wet_Boots]

If the soil is really sandy, the Hunter gear drives might not be your best choice. Someone who works almost exclusively in sandy soils might have some alternatives. I would consider Rainbird R-50 heads, from my own experience in seeing how well they pop up and retract without leaks or problems. Sandy water wouldn't trouble them. They can work at low water pressure. But they won't spray as far as gear drives will.

System layout is up to the one person who knows the details of the layout. Get out your drawing of the property, and start locating sprinkler heads. Put a head in every inside corner. Then begin to 'connect the dots' by locating heads evenly spaced between them. Use a drafting compass to draw circles around the heads. Despite what numbers you might read, for the sake of designing this way, don't expect more than 35 feet from a gear drive head.

The elevations may be a bit of a burden, depending on what your plumbing codes are. I would have to employ a pressure-robbing RPZ device, when a property slopes uphill from the house. You might be able to use a Double Check Valve Assembly. If you do require an RPZ, you might end up balancing the system to use less water, so the supply pressure could be 60 psi or higher.

[jabbo]

Thanks for the replys. As far as the backflow I'm not required and don't think I am going to use it even after all the preaching about them from you guys! And as far as the elevation change my connection will be made at my well so everything will go down hill from there. I thought this was better than having to go up hill? One thing I'm kinda unsure on is what Bicmudpuppy said about full circle heads being 100%, 3/4 or 270 heads being 75% and so on. Does this refer to gpm? If so I got ya. I am starting out with 50 psi so if I don't use a backflow preventer I would think that there would be no more than around 10 psi or less in loss to the heads. You think thats pretty accurate? So I'm thinking maybe around 40 psi for the heads to run on. Wet Boots, you say I can probably get around 35 ft from a pgp with the right pressure. So I was thinking about running maybe 4 full circle pgp heads with a # 7 nozzle at 3.0 gpm. The hunter book says the radius would be 40' so if I shoot for 35' I should be o.k. Another question is that if I use different nozzles for the half and quarter circles want that decrease my radius on those heads. Like I said, I'm in the learning process so bare with me. I have just about got my yard drawn out on a piece of poster board for the extra room and will start drawing in the heads. Another thing I was wandering was what size mainline and laterals would you use, I have 1" 1/4 (I think) that I installed to check my flow and pressure. One more question, do I have to put mostly "like" heads on a zone or can I put whatever just as long as I stay within my gpm range? Because if I can't hit whatever heads are in a group that is going to be alot of different pipes going everywhere! While I'm asking, what type of valve do you recommend,flow control, anti siphon, etc...

[Wet_Boots]

Whoa! Back up. Backflow not required? Not on your tintype. This is a well water supply feeding your home, isn't it? That puts it under the prevailing housing codes. In your state, possibly the SBCC. Every one of these regional housing codes mandate the protection of the water supply in the house. There are no local exceptions permitted. What a locality may do is raise the bar, and require backflow protection above the written minimum, but they cannot waive the plumbing codes for anybody. If any official tries to tell you different, ask them to put it in writing on their letterhead and sign it and date it. Don't hold your breath. Another consideration is what would happen to an exisiting system without backflow, when the backflow does get added (and it does get added in a hurry, when someone finds they cannot sell their house without it) and the resulting loss in water pressure ruins the sprinkler coverage.

If this is a well that has no connection to your home, then housing codes wouldn't apply, but even if there is no current requirement to protect the well water (It's the state's water, not yours, and they get to set the rules) it would be prudent to allow for the future installation of a backflow preventor, and the pressure loss it would create.

Either way, if the well is at the property's high point, you can feed the system through a pressure vacuum breaker, located so it's a foot-and-a-half higher than the highest head or pipe it feeds, and be good to go for any regional plumbing code. It's money well spent.

Locate the heads first, then worry about how you will group them. In the old days, you would group full-circle heads together, and so on, because the nozzles weren't interchangeable. Nowadays, you just swap nozzles, to make each head's consumption proportional to its arc. If you can avoid mixing quarter-circle heads with full-circle ones, that will give you a wider choice in nozzles.

[jabbo]

What I meant by not required is that we have no building inspector in our county. Not for electrical, not for plumbing, not for hvac or anything. So I figured there were no requirements in place as of now. Down the road probably yes. So I will take your word on it and install one. So what is the psi loss for one of these at my flow?

[YardPro]

30 gpm is a bit of a reach. Expect closer to 25 gpm if you install a 3 horsepower pump.


all depends on where you are.

here we get 30 gpm from a 1hp pump.

our commercial wells have 5hp and put out about 100 gpm.

[bicmudpuppy]

You almost lost me on this thread completely the minute you said no backflow. A DC will cost you less than 5psi. As to laying out your valves, split your main and you can group the permimiter heads seperately fairly easily. Again, look at the 7x7 table I typed for you. By using the equivalent of 1/2 circle nozzles on the fulls and running them twice as long, you also beat the remarkable range of distance those hunter nozzles produce.

[Wet_Boots]

all depends on where you are
Sure does. He's on a hill. You're on the flatlands. He gets 13 gpm from a horse-and-a-half pump. That's why 30 gpm from a three-horse isn't likely to happen for him.

Of more benefit, what are the heads you're using in the sandy soil? Seen any long term performance trends in various equipment? Do you use any RPZ devices for code compliance?

[jabbo]

The reason for the low gpm's is that its 160 ft to the water!!

[Wet_Boots]

At least it's not 500 feet to the water. The pressure loss in the Pressure Vacuum Breaker mentioned earlier is a bit less than 5 psi. The pressure that is lost in the backflow preventors and zone control valves is a factor you just have to live with. You can hold it under 10 psi total loss from supply to heads if you select properly sized pipe.

Since you're dealing with slopes, you have to allow for the distance lost when a head sprays uphill. A 35 foot spray can drop below 30 feet.

[jabbo]

So if the psi loss is under 5psi in the backflow preventer and I do my pipe sizing right I should be able to keep the pressure at the heads to around 40 psi if I got 50 psi at the pump. I was thinking about running 1"1/2 for the mains and 1" for the laterals.Looks like around .5 psi loss for 1.5" schd. 40 per 100 ft. Looks like the valve loss will be around 1 psi.

[Wet_Boots]

Zone valve loss will be more like 3 or 4 psi, for a 1 inch valve, which is what you would use here. Remember that the 50 psi number is not 'etched in stone' but simply the pressure you observed at 13 gpm. If the flow is slightly reduced, the pressure will be higher, and vice versa. Elevation also changes pressure, at the rate of 0.43 psi per foot. If you have a 300 foot run from pump to the first head on a zone, then one-and-a-half inch pipe would gain you a psi or two, compared to inch-and-a-quarter.

[jabbo]

Another question. 1" and a 1/2 mainline, 1" laterals. How do I know if I need to downsize to 3/4" at the end of a zone like I read some people have done?

[bicmudpuppy]

Another question. 1" and a 1/2 mainline, 1" laterals. How do I know if I need to downsize to 3/4" at the end of a zone like I read some people have done?
You've got to reverse your thinking to understand pipe sizing. Pipe size is a result of flow within the pipe. The more flow (larger nozzles or more sprinklers) the larger pipe size. 1/2" pipe is good for about 5gpm, 3/4" pipe will carry 10gpm, 1" pipe velocity gets high at 20gpm. Charts are available. In low pressure, larger pipe sizes reduce your friction loss. If pressure is not a main concern, then the velocity of that flow within a pipe size becomes a concern. Most state a standard of 5fps for pvc, but many design texts will accept velocities that aproach 7fps or even a bit more. So, pipe size is a product of how much flow from the point of reduction on. When you are far enough down stream to have reduced flow to an acceptable level for smaller pipe, then using smaller pipe is (or can be) more economical and more hydraulically correct from a design standpoint.

[jabbo]

I thought I remembered having a 1"1/4 supply going to my house from my well tank and just tied on there with a tee to check my gpm's last year,but it is a 1". So my question is how much more flow(if any) will I get when I go up to a 1"1/2 mainline for my system? The reason I'm asking is that I'm about thru designing and I want to make sure I have everything right.

[Wet_Boots]

It's all pressure loss, and it depends on flow and pipe length, and can be checked on charts. What heads are you considering using?

[jabbo]

I'm going to use pgps. On the zones with all full circle heads I've got 3 per zone. I probably could have put more but I wanted to make sure that I had enough water on each head for it to perform right.

[Wet_Boots]

Probably a good choice, although some might favor stainless-steel I-20's if the soil is terribly sandy. If so, do mount the heads high, to protect the seals from the sand. The soil will tend to build up, once the lawn is flourishing.

[jabbo]

I have heard of alot of people using them and figured they had to be good heads. So, do you think I will gain any flow or not. I'm not really trying to gain any just trying to make sure I'm going to use up all thats there on every zone. I'm going to run 1"1/2 mainlines and 1" laterals. Another question is about running pipe. Are there any major rules I need to follow when I start drawing my pipelines. I'm going to put my valves out in the yard just because I have so many zones. Can you give me some do's and dont's for running the mains and laterals.

[Wet_Boots]

Once again, it's all pressure loss, and you know the flows and pipe lengths, so it's up to you to check <a href=http://www.rainbird.com/pdf/turf/ref_Friction_Loss_Characteristics_p2.pdf>friction loss charts</a> to see what the losses would be, and to choose appropriate pipe sizes.