Large openings that are less susceptible to clogging can be used. Variations in emitter operating pressures due to elevation differences and pipe friction cause smaller variations in the discharge from vortex emitters.
Pressure-compensating emitters attempt to overcome the hydraulic constraints imposed by orifice or long-flow-path emitters and to provide a constant emitter flow rate. Usually, an elastic material, which changes shape as a function of pressure, is used separately or in combination with orifices or small-diameter conduits. These emitters usually allow only small changes in emitter flow rate as pressure is changed within a given design range. Pressure-compensating emitters allow the use of smaller lateral pipe diameters, longer laterals, and/or fewer manifolds. Pressure-compensating emitters may be the only way to achieve uniform water application when slopes are steep or when the topography is hilly and uneven.
Automatic flushing emitters are less susceptible to clogging. In these drippers, the flow passages open more widely at low pressures than at the normal operating pressures. This results in high flow rates, which flush the system and wash away any deposits that may otherwise clog the emitters. On/off flushing emitters flush for only a few seconds each time the system is started and again when it is shut off. Continuous flushing emitters are constructed so that they can eject relatively large particles during operation. They do this by using relatively large-diameter flexible orifices in series to dissipate pressure. Particles larger than the diameter of the orifices are ejected by a local increase of pressure as the particles reach each flexible orifice.
Emitters flow rates are described for design purposes by experimentally determining flow rate as a function of operating pressure (Fig. 5.35). This empirical emitter-flow equation is
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