# Sprinkler line question

• posted on October 24, 2008, 5:04 am
I have a few busted sprinkler heads so I decided to dig a trench along the line and examine the line. I was amazed that in a stretch of 60' the pipe went from 1-1/2" diameter to 3/4" to 1" then back to 3/4" as it goes downstream. I think over the year sections of pipes were being repalced or modified.
I assume the changes in the diameters like this would cause unnecessary pressure loss or even un-uniform pressure for each sprinkler head on that line? So I am planning to replace them all with a long stretch of pipe with the same diameter. I am not sure what diameter to use, should I stay with 1-1/2" or reduce it to a smaller diameter? This line runs down the middle of a side yard about 25' wide and 75 feet long but the run is only 60'. How far apart should I space the sprinkler heads if I used 360 degree heads?
Another question is at the end of that 60' run is a big tree occupying the end of that yard, and the root system is such that I cannot trench any further. I am wondering if it's ok (will there be enough pressure) to put a big 360 degree impact rotor sprinkler head on the end of the pipe run to try to cover the area of the tree, but I don't know if it's going to have enough pressure to run that rotor sprinkler at the end of the line. How can I determine that without actually gluing up everything to try it?
Thanks,
MC
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• posted on October 24, 2008, 10:00 am

Gee How can anybody even try to make a guess without knowing how many heads, of what gpm, and water pressure.
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• posted on October 24, 2008, 12:28 pm

Google 'lawn irrigation tutorial'. There's a guy who has a great web site with all sorts of planning information. Your question can't be answered without more information.
R
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• posted on October 24, 2008, 3:04 pm

One thing is for sure, you don't need 1 1/2" pipe to water a 75 X 25 area. The 3/4" is what would typically be used. So, you can go ahead and change it if you want. but if what's there works except for the heads being shot, you're not improving anything, just making more work.
As to exactly how to place the heads, what kind to use, etc, there are varying theories and websites that have guides and info.
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• posted on October 24, 2008, 4:37 pm

One thing is for sure, you don't need 1 1/2" pipe to water a 75 X 25 area. The 3/4" is what would typically be used. So, you can go ahead and change it if you want. but if what's there works except for the heads being shot, you're not improving anything, just making more work.
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I went with 1" pipe for all my longer runs. A 3/4" pipe with many heads on it would have a lot of pressure drop. Unless the pressure is very high, the OP may have problems by the end of the line.
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• posted on October 24, 2008, 2:54 pm
MiamiCuse wrote:

If you plan to replace lines and heads, the simplest thing to do is to use one of the manufacturers free design services. You send them the dimensioned sketch of the yard, water supply info, etc. and in a week or two they send you a full design with all the piping and sprinkler head specs. Get this design and then just use the portion of it you need, and as other areas need repair, just refer to the plan again for what to replace things with.
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• posted on October 24, 2008, 3:46 pm

Toro has a pretty good sprinkler installation guide, here: http://www.torodesign.com/iguide2/intro.html
The process is pretty generic - space heads for full coverage, determine GPM (gallons per minute) needs vs. supply capacity, split heads into circuits, start digging and gluing.
For best coverage, the spray patterns should overlap completely - i.e. if the head says 15' spray radius, the heads should be about 15' apart.
Determining you water pressure and flow capacity in GPM will tell you how many heads you can put on one circuit - add up the individual GPMs of all the heads - should not exceed the supply GPM, if it does, add another circuit.
Jerry
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• posted on October 24, 2008, 4:34 pm
Yes I did look at some of those web sites for the calculations. However the problem is I have two runs that serves different parts of the yard and I have yet to discover all the heads and there are areas that the two runs partially overlap and I do not know which head is from which run. I fixed a few heads last weekend and once they are fixed I then realized I have another stretch somewhere else that when along the perimeter of the property line then under the driveway and back up on the other side of the sidewalk.
So what I am trying to say is it's impossible for me to know all the heads and all the run and branches at this time without me digging them all up, so I am trying to use the best judgment I can to fix a partial section of it by knowing that the existing configuration works so trying to isolate the subsystem and establish it's boundary conditions. The water supply is from a well pump.
MC
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• posted on October 25, 2008, 1:42 am

I would think your best plan would be to repair the system using your best information from the existing heads and pipes. Then try it out and figure out what needs to be changed or added. I have done that a couple of times and it worked for me. Oversize pipes or sections of pipes do not cause any problems.
Don Young