Question
I have a sprinkler system that run from a well, or at least that is what I have been told.  I have a pump that sits next to a control panel that activates the various zones to water the lawn. Recently, some of the zones work, and some of them don't.  The pump is very old and is very loud when it runs.  I plan to replace the pump, and wonder if there is a priming process I need to do to kick start the sprinklers?

Answer
Thanks for the question. Sorry I didn't answer sooner.
Off -hand I would say you pump is in need of some help or replacement. Usually, when they run they're fairly quite unless the bearings or impellers are going bad. There is a situation called cavitation, but I doubt that the problem unless the well you are drawing from is slowly getting plugged. In that case, it would not allow enough water to the pump making the pump sound like it was full of marbles.
I'll need a bit more info to help further. Is this well only for the sprinkler system? What size well is it, if you know? Do the zone that run have approximately the same number of sprinklers as the zones that won't run?
One thing you could do, is look for any leaks on the suction side of the pump. (Between the pump and the well). A tiny air leak drastically reduces a pump efficiency.

Matt