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The last 8 posts

Sunday, October 9th 2016, 4:02pm

by Wet_Boots

..... being a numbers person .............
Well, there's your problem right there. Numbers aren't enough. Unless you get a pressure gauge and some sprinkler heads and watch them perform on a test stand in the field, you won't know when and where sprinkler performance charts are fibbing. Charts will be accurate about flow, but there it ends.

When you abandon the pipe dream of running the entire yard from a centrifugal pump and gear drive rotors throwing 39 feet, you might dial back your expectations and create something that actually works. For the money, you use a jet pump and break the system into zones.

By the way, the sprinkler companies make it plain that you are expected to be using head-to-head spacing from border to border. Heads on the perimeter spaced at the numbers supplied by the manufacturer are still going to provide effective coverage when it turns out they were fibbing about spray distance. Your "band of circles" design is likely to be a disaster if you don't step away from the catalogs and apply real-world knowledge. What you really need to do is get a couple of the Maxipaws and try them to see whether they fit. Going strictly by the flow numbers, you can run 9 of them at once, possibly from a GT10 pump, using the smaller black 07 nozzles.

If you are wondering "why is this?" the answer is more or less "impact heads" - today's gear drive rotors had to compete against impact heads when they were first introduced, and they never could spray as far as brass impact heads, so there began a tradition of performance charts that tried to make the new technology look as good as the old. There might be a test result in a sealed warehouse with absolutely still air, that matches what you see in a catalog, but that is meaningless for actual design work. So the tradition has become distance numbers you don't bet the ranch on, along with design instructions that make their numbers accuracy unimportant.

Sunday, October 9th 2016, 2:48pm

by 7474

Thanks for your responses. Your time and assistance is appreciated.

I started this project thinking I would just use a sprinkler pump and put out impact sprinklers. This then changed to rotors since they had lower GPM requirements, allowing me to run more at one time. This then progressed to the current underground project because I didn't want to set-up things every week.

My first pump was from Harbor Freight.....

The first version of my irrigation project used this pump and the RainBird 42SA+ with a 1.5 nozzle that was rated at 33' radius. I had the rotors attached in series with 50' 5/8" garden hose spaced 33' apart, just like in my original post. With the rotors in series and over 300' of 5/8" garden hose I was able to have 6 of the 8 rotors pop up and provide full head to head coverage.

So, being a numbers person and looking at the specs of the Goulds GT20 and upgrading to 230' of 3" mainline (total psi friction loss of 1.081 - at ~70gpm at 35psi and 5' suction lift) coupled with the rotor performance info from RainBird I am having a difficult time understanding how my coverage would be insufficient. Especially, since I was getting head to head coverage on the same set-up for 6 of my 8 rotors on a weaker pump and far smaller pipe (garden hose). I understand the tree area, but this could be solved with the placement of 2-3 additional rotors near the sidewalk.

If I am getting ~70gpm at 35psi from the Goulds GT20 and I have the RainBird 42SA+ with a #6 nozzle (5.2gpm/52-58gpm over 10-11 rotors) at 35psi showing a 43' radius on their performance chart with rotors spaced 33' apart, seems my coverage would be more than sufficient.

I understand the statement regarding radius not being greater than PSI at the rotor, but again being a number person this would mean the 42SA+ is overrated on the nozzle chart anywhere from 3% to 23%. Even the PGP Ultra shows radius greater than PSI on their blue and red nozzle performance charts. This to me would make designing a system very difficult if the numbers weren't standing up in the real world. Or, it would make the system very inefficient if you were designing a system with a max head to head distance of the psi at the rotor when in reality you were getting anywhere from 3-23% greater coverage.

Thanks again for all of your input, you have given me much food for thought. Even thinking that perhaps I will continue to leave the irrigation to mother nature as she has been doing for the past 10 years.

Friday, October 7th 2016, 4:32pm

by SunCoLawns

It does not matter what kind of pump or heads you use. It is never going to have good coverage with this kind of design. As long as you are going to spend all that money on a pump set up, why don't you do it right the first time?

Friday, October 7th 2016, 10:55am

by Wet_Boots

It all kind of depends on how much spray distance you really need for your intended design to function. One detail I left out of the earlier post is that larger nozzle sizes in the gear drive rotor heads like the 42SA have very poor water distribution at low pressures. The larger the nozzle, the more pressure you need to give it, in order to get a good spread of water.

As it is, your all-at-once 'economy' design will be very difficult to winterize by blowing air through it, unless you have a tow-behind jackhammer compressor.

Being that more water pressure equals more spray distance, you might do better to start with a different kind of pump. A Shallow Well Jet Pump is like a centrifugal, but it adds some internal recirculation in order to create more output pressure, at the cost of having less flow. It's a good tradeoff. You get more useful pressure, but not so much pressure that it can break anything in a system where a stuck-closed zone valve might prevent water flow. I use Goulds J+ shallow-well jet pumps.

If you design your system with a jet pump and several zones, you can operate at higher pressures and get more spray distance, and not need to use large diameter pipe to conserve pressure. You could get by with as little as a 3/4 HP jet pump running two or three heads per zone, should it be that you were determined to not use any pipe larger than one inch in diameter. Also, the system divided into zones allows for fixed-pattern spray heads in separate zones, to cover areas you left out of your original design.

Thursday, October 6th 2016, 6:13pm

by 7474

In Ohio.

Looking at the Goulds GT15 now. Thoughts on this pump?


Thursday, October 6th 2016, 5:56pm

by Wet_Boots

A few important notes here.
  1. the Wayne LS200 is one of their "Lawn Sprinkler" pumps - the name is nowadays a misnomer, because the pump is a simple centrifugal design that will not efficiently develop enough pressure for proper sprinkler operation - centrifugals are most efficient at pressures below 30 psi

  2. the Rainbird 42SA+ will never, not ever, spray 39 feet with 25 psi at the head - it is a good rule of thumb to never expect a rotor head to have a spray radius, in feet, that exceeds the head pressure, in psi

Those points established, there is a way to work with the primitive design idea shown here, while at the same time allowing for a more conventional layout. Change your sprinkler choice to the Rainbird Maxipaw impact head. Impact heads are the one rotor sprinkler that can exceed the pressure/distance constraint. Just the same, don't expect more than 35 feet spray radius.

One problem with the ultra-simple layout can be summed up in a single word. Trees. They get in the way. Dead stripes of lawn.

Play around with your design a bit more. Try a layout with half-circle heads along the street and driveway, and spraying away from paved areas near the house. You can easily feed 20 or more of the Maxipaw impact heads from your pump.

Watering everything at once has some advantages, but you don't save a ton of money doing it. The reason is that you can pump a very large flow of water, but at such a low pressure that you are forced to use pipe sizes large enough to insure you don't have any loss in pressure though the entire system. That means a minimum of 2 inch pipe coming from the pump, or even larger if you used more of the pump capacity. You do have an advantage of highest possible bang for the buck, in turning electricity into gallons of water sprayed on the lawn, and you also avoid issues with lake water being pumped through sprinkler zone valves.

There are better pumps than the WLS200 out there. If I were doing this project, I would be looking at the Goulds Irrigator pumps.

Where is your location? If you don't have winter freeze worries, some other system design possibilities might apply.

Thursday, October 6th 2016, 2:19pm

by 7474

Thinking about changing the pump out to a Goulds GT15 Irri-Gator. Found an online place with prices almost the same as the Wayne. The Goulds is higher pressure and seems to be more efficient for 1/2 horse less.

Also, I have read the Goulds are very reliable?

Wednesday, October 5th 2016, 8:12pm

by 7474

Running 9 rotors over full yard at once

I would like to run (9) rotors at the same time to water my yard all at once.

The red dot is the pump, the blue dots are the rotors, and the yellow line is the mainline, disregard the orange line.
The furthest distance from the sidewalk to the shrub beds is 40 feet. The water is from a lake and I am not concerned about the overspray.

(9) Rainbird 42SA+ with #6 nozzles at 25psi use 4.2gpm each (total 37.8gpm) with radius of 39'; spaced ~33' apart.
230' mainline of 2" SCH 40 PVC - at 40gpm = 2.645psi friction loss over the 230'
laterals are 1.5" SCH 40 PVC
pump will sit less than 2' above water level
elevation from pump to highest sprinkler is 10'

I originally was thinking of using a 2HP Wayne WLS200, but I am thinking that is going to be overkill since at 5' head and 25psi discharge it supplies 80gpm. However, it is only $30 more than the 1HP.

Am I thinking about this and running the numbers properly? Any guidance would be greatly appreciated.

Thanks for your time.