Note that if the operating pressure is greater, a greater elevation difference is required to cause a 10 percent variation in flow rate. If the flow rate is altered on one portion of the system, the remainder of the system will experience some change in flow. Thus, when elevation differences exist, regulators are installed on all sprinklers. The second point to remember is that none of the regulating devices function until the mainline pressure exceeds the rated operating pressure of the regulator. Typically, the mainline pressure must be at least 5-8 psi greater than the pressure rating of the regulator.
Operating costs are greater for a system equipped with regulators.
An elevation difference on the outside of the irrigation system involves a greater amount of water and a greater irrigationd area than a similar length of the system located near the pivot point. Small changes in sprinkler output on the outside portion of the system lead to large pressure differences on the remainder of the system. Particular attention should be paid to the outside portion of the irrigationd area. The number of acres affected by a variation in flow rate before regulators are economically justified varies. The actual number can be based upon the severity of the flow rate variation, the crop under irrigation, the amount of irrigation water applied annually and the price to be received for producing a greater or higher quality yield.