The correct design of a micro-irrigation system cannot ignore the knowledge of the characteristic delivery curve relating to the particular type of dripper to be used, which represents a functional link between the flow rate delivered by the dispensing device q [L³ T-¹], and the piezometric height corresponding to the operating pressure h [L] of the same and takes the form [Wu, Gitlin, 1974], [Howell, Hiler, 1974 a, b], [Karmeli, 1977]:
where: q = flow rate delivered[L³ T-¹] h = Operating pressure [L] K = Flow coefficient x = Flow exponent.
K and x are two parameters that characterize the type of dripper. These parameters can be obtained experimentally and depend respectively on the geometric characteristics and the motion regime of the water current inside the dripper [Keller, Karmeli, 1974], [Bralts et Al., 1981], [Vermeiren, 1983], [Mandramootoo et Al., 1988].
Figure 1 – Characteristic curve of the regulators
The value of the flow coefficient K is related to the physical dimensions of the water pipe. The value of x can be between 0 and 1, according to the type of dispenser; the lower the value of x, the greater the pressure compensation of the device will be and it assumes values close to 0 in the case of pressure compensated emitters, the flow rate is constant in the specific range of operating pressures and the uniformity of the system will be theoretically perfect (regulators at complete pressure compensation).
In the case of nozzles without pressure compensation, the value of x depends on whether the flow of the nozzles is vortex, wholly turbulent, wholly laminar, or to some extent between turbulent and laminar, so that we have values close to 0.5 in the case of purely turbulent flow and values tending to 1 in the case of laminar flow. Sometimes, for dispensers in which an increase in the orifice section is determined as the pressure increases, values even greater than unity can be obtained.
