Question
'd like to know the lifespan of a Nelson irrigation system, namely the pipes.  I
have a young man who claims to be an irrigation expert who comes out to
my house to turn on my system for the season.  He tells my wife the main
pipes need to be replaced along with four sprinkler heads because they don't
put out enough of a wide pattner/water.  The system was installed 13 years
ago and I'm not sure if this diagnoses is correct or not, as there doesn't
appear to be any leaks or problems.  We just spent a bunch of money last
year to replace an underground leaky valve.

Answer
Hi Scott

As far as I know, Nelson doesn't manufacture pipe of any sort, other than maybe swing pipe.  The typical life span of PE (polyethylene) is about 10-15 years and Class 160 PVC even longer, as long as the system has been adequately winterized every year.  

If you suspect there is an issue with the coverage provided by your current sprinklers, I'd suggest you turn on the system manually and look for the following during operation:

1.  Head to head coverage - This is where the water distributed from one head actually reaches an adjacent head and vice versa.  It is important to ensure this type of coverage because even a brand new single head by itself has poor coverage, so to offset the inefficiency of a single head, a good design sees heads throw water to over-lap each other.  If they fall short, you may have a flow issue.

2.  Area of coverage - While each zone is running, look at what is being watered and determine if there are any dry spots.  Conversely look for any areas that may be getting too much water.  

3.  Leaks - If there is a line leak, it won't take too long appear.  Let each zone run for approximately 5-7 minutes and look for excess water, or a soft and mushy area of the zone which would indicate an accumulation and subsequent leak to tend to.

Ultimately you are looking for good coverage to sustain your landscape and keep it healthy while using the least amount of water possible - conservation is the key.

Let me know how you make out and provide some feedback when you're finished.  I'd be happy to discuss the results.

Take Care

Tony