As a general rule you should hire a professional designer if you need sprinkler spacings greater than 45 feet. Figure a minimum of 15 PSI more will be required for the pipes and valves.) The small rotors sold for residential use work best at 25 to 35 foot spacings, although with careful design some models can be spaced up to 50 feet apart. (Caution: you will actually need more pressure than 35 PSI to run the system due to pressure loss in the pipes and valves between the water source and the sprinkler. When selecting a rotor keep Stryker's Rule in mind "the water pressure at the rotor head (in PSI) must exceed the distance (in feet) between the heads.") Thus if you want to space rotors 35 feet apart you will need 35 PSI of pressure at the rotor. Most rotors require a lot more water pressure to operate than spray-type sprinkler heads. There are also rotors available for spacings farther apart than 55 feet but they are typically only used for golf courses. There are rotors available that can be spaced closer than 18 feet but they are generally not cost effective, as a spray sprinkler will work well at this spacing and cost less. Typically rotors are used for sprinkler spacings from 18 feet to 55 feet apart. What situations work best with rotor-type sprinkler heads? Typically they use an electric motor to move the nozzle. The size and shape of the area to be watered is programmed into a computer, the computer then controls the sprinklers, telling them where to move the stream and how much water to apply in each spot. This works something like when you use a hose to water the yard, and you move the nozzle of the hose around to make the stream of water fall on different spots. Sometimes called robot sprinklers, these sprinklers direct a stream of water to fall on specific spots. However, it operates a little different from a traditional rotor. I need to mention a new type of sprinkler, which I am classifying as a rotor since it utilizes a moving stream of water. A preinstalled nozzle or limited nozzle tree is common with many of the prepackaged rotors sold at discount stores. Some rotors, however, still come with a single, pre-installed nozzle, and some come with stripped down nozzle trees (with only a few of the available nozzle sizes on them.) If you want the whole set of nozzles with these less expensive models, you must purchase them separately. You might be able to green it up by installing a larger nozzle in the rotors surrounding the dry spot. Multiple nozzles are a big advantage, as you can change to a different size nozzle if needed to help balance your system. Save the rest of the nozzles, you may need them later.
Just remove the nozzle you want from the tree and install it in the rotor. Often these nozzles come attached to what is called a nozzle tree. Most rotors now come with a set of nozzles rather than a single nozzle. Multi-stream rotors are fascinating to watch but tend to be higher maintenance than the other types of gear-drive sprinkler heads. The prettiest of these are the multi-stream rotors (or stream-rotor) where multiple streams of water rotate over the landscape one after the other. These gear-drive rotors have one or more streams of water which rotate silently across the landscape. The water moving through the sprinkler spins a turbine, this turns a set of gears, which turn the nozzle. As with cam and ball drives, only the nozzle on a gear-drive moves. Thus the impact rotors have now been almost completely replaced by gear-driven rotors, which are very quiet, rotate smoothly, are lower maintenance, and much smaller in size. While impacts do an acceptable job of irrigating, the jerky motion of the impact drive tends to make them rotate in a less than uniform manner. Most of these ball and cam drive sprinklers are no longer sold, but a few, like the Rainbird R-50 (they don't call it a ball drive, but it is) are still available. With ball and cam drive rotors only the nozzle moves. These are also impact sprinklers, however the impact is caused by either a cam or a ball bearing inside the body of the sprinkler. You may run into rotor-type sprinklers called cam drives or ball drives. You probably know the impact sprinkler best for the distinct sound it makes when operating- tooka, tooka, tooka, tic, tic, tic, tic, tic, tooka, tooka, tooka, etc. It is rotated by the impact of a swinging arm which repeatedly strikes the body of the sprinkler, causing it to rotate slightly each time. The example which most people are familiar with is the "impact" rotor sprinkler (often improperly called a "rainbird", Rainbird is the actually the trade name of a sprinkler manufacturer.) The impact sprinkler is mounted on a bearing that allows the entire sprinkler body to spin in circles. Rotor is the term used to describe the various sprinklers which operate by rotating streams of water over the landscape.