Sprinkler rotor options
Q: Which has the greater benefits-closed-case or open-case rotors?
Frank Simon, president, Landscape Irrigation Consulting (Dana Point, Calif.)
The main reason we prefer using closed-case rotors is a reflection of the type of projects with which we are involved. Our project sites consist of slopes that usually are planted with shrubs and ground cover, achieving a less-maintained and more natural look, as opposed to manicured, maintained, open turf areas.
On one particular site, we installed open-case rotors at the top of the slopes prior to the introduction of the 12-inch closed-case pop-up rotors. The problems we encountered with the open-case rotors were twofold. First, the pop-up height was not sufficient to clear the plant material. Second, runoff water carrying loose materials would fill the cases with debris.
Additional problems occurred later during the plant-establishment period when branches interfered with the rotor operation, preventing proper coverage and rotation. Closed-case rotors, however, have a 12-inch pop-up range and prevent debris from flowing back into the case. Furthermore, the fact that the internal workings of the rotor do not have direct contact with the surrounding plant material enables the head to perform within tightly grown areas of plant material.
Granted, the open-case rotor is much more cost-effective relative to repairs. But comparing the cost to replace lost plant material and maintaining clearance around the heads for proper operation and coverage, you could forego the lesser repair cost to the functionality of the closed-case rotor. The closed-case rotor has more nozzle combinations, thus achieving a better precipitation rate among different heads.
Brian E. Vinchesi, design engineer, Irrigation Consulting & Irrigation Inc. (Pepperell, Mass.)
When we talk about open-case rotors, basically we are talking about impact-type vs. close-case gear-driven sprinklers. When you properly install open-case rotors, they will outperform a closed-case rotor in many ways. In general, a sprinkler at the same gpm, pressure and spacing will provide a better distribution uniformity, a better coefficient of uniformity and a better scheduling coefficient with an impact vs. gear-driven sprinkler. These three uniformity factors all add up to better irrigation coverage and less water use for the same area and price. Additionally, impact sprinklers are better in the wind and are much more forgiving when spaced improperly.
Open-case sprinklers are easier to adjust than closed- case. A simple setting of the stop points sets the arcs, and you do not have to wait for the sprinkler to rotate. Simply turn the sprinkler to check the arcs. Open-case sprinklers are easier to repair; you can buy the parts and rebuild the sprinkler. You must replace the entire gear-drive assembly or similar component of a closed-case at a much higher cost. More material choices in terms of plastic vs. brass exist with open-case rotors. And open-case rotors do not have problems with oil leaking or non-lubrication. Impact sprinklers also provide faster rotation speeds, which provide for more scheduling flexibility.
If you install an open-case rotor so that the case can drain, it will not collect debris and will give years of service with little to no maintenance, while providing a more uniform application of water.
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