I bought an old utility pump from a retiring landscaper last year, and have been using it to pump water from the river behind my house to water my back yard/field (this is part of the continuing recovery from Hurricane Irene, which filled my field with sand piles, some 8-feet high).
In any case, we've had rains recently, and all of my sprinklers stopped working. After checking the pump, which is blasting water (it's a 3.5 HP unit), we finally figured out that there is sand and grit in the water lines, which clogged up the sprinklers. Before the rains, the pump was feeding all of the 10 sprinklers I have connected to the pump without a hitch.
I'm using $15 rotary stake sprinklers, which water about a 50' to 80' feet diameter each. Links to them are below: