Question
Jeff -- My town has reduced the water pressure and this has negatively impacted my irrigation system. The town sent out their engineers and I called my irrigation company. The irrigation company wanted to put in a pump ~$2000. The town suggested replacing some of the spray heads and replacing with rotator heads. I called the irrigation company and they said they could do that and it might work. Specifically, we'd cap 8 heads and swap out 4 heads for 3500 models and 3 for 5000 models. New estimate ~$500. When I looked at the pricing on parts I noticed that the heads were more than a 100% marked up. When I asked about this the guy said that was to cover his overhead and I could do the work myself. So now, I'm thinking about doing the work myself but have a number of questions:
- Currently I have Nelson heads in the system, can I use other manufacturers in the system without creating additional problems?
- How do you cap heads?
- How difficult is it to replace spray heads with rotators? Is it as simple as screwing in the new head to the same base or will I need to replace part of the piping with new pieces?

Basically, I was wondering how hard is the to do and how do I do it?

Thanks.

Answer
You can mix heads with little problem, but there are a few considerations.  You want to try to match the precipitation rate (the water the sprinkler puts out), and the pattern (the area that the sprinkler covers) as much as possible.  
To cap a head, you dig around it, exposing the base of the head and the riser supplying it.  Unscrew the head, and use a threaded PVC cap fitting to replace it.  Its a good idea to seal the threads on the riser with teflon tape.
Its easy to replace the heads, but it may take some tweaking to make the system work well.  Like I said, you just expose the pipe and screw on the new head.  Shouldnt be a need to replace any existing piping unless you have coverage problems, and need to add a head where one was not before.