Type and hydraulic functioning of the emitters
Laminar flow emitters
In laminar emitters (microtubes, spiral drippers) the water current moves slowly and regularly, flowing smoothly and at low speed.
Figure 1 – Laminar emitters
Laminar flow devices regulate water flow by dissipating energy by friction against the walls of the water conduit. The narrower or longer the duct, the greater the friction resistance opposed to the water flow and the lower the resulting flow rate. Ultimately, the pressure drops that occur inside the dispenser are only of the continuous type. Therefore laminar flow devices typically use long and narrow passageways. Examples of laminar flow devices are microtubes, capillary tubes and spiral drippers.
The drawbacks of these devices are represented by the fact that they have a certain sensitivity to pressure variations (their flow rate varies considerably with the variation of the pressure) and that they are more subject to clogging, due to the low speed of water flow at their internal and the narrowness of the diameter of the internal passages.
Laminar flow devices are also sensitive to the viscosity of water, which means that their flow rate will vary as the water temperature changes.
Turbulent flow regulators
In dispensers operating in turbulent regime (orifices, double chamber pipes, labyrinth drippers) the fluid particles move rapidly with irregular and random movements.
Figure 2 – Turbulent flow emitters
The turbulent flow devices regulate the water flow by dissipating the energy in the friction against the walls of the duct, and through the collisions that occur between the water particles themselves. Compared to laminar dispensers, these dispensers have larger passage sections and generally higher current speeds. The pressure drops that occur inside them are generally both continuous and localized. In addition to orifice-type dispensers, tortuous path drippers are to some extent turbulent flow, which rely on both turbulence and wall friction to dissipate energy.
Compared to laminar flow devices, turbulent flow devices have the advantage of having shorter and wider paths with higher flow speeds, which are useful factors in terms of resistance to clogging. Also, if a dispenser is truly turbulent flow, its flow rate will be less sensitive to pressure changes than laminar flow devices and will not be affected by water temperature.
Vortex dispensers
Vortex regulators are designed to take advantage of the fact that a vortex, or swirl, has less pressure in the center. As the water rotates inside the vortex nozzle, centrifugal force pushes it towards the outer edge of the vortex, which produces a low pressure area in the center.
Figure 3 – Vortex emitters
The point of emission, usually an orifice located in the center of the vortex, senses a lower pressure and therefore delivers a flow rate that is correspondingly lower. A well designed vortex regulator is less sensitive to pressure changes than a turbulent flow regulator.
Vortex dispensers have the drawback of having very narrow water ducts, which are easily clogged by earth particles or other contaminants. So vortex drippers will require a high quality filtration system and careful water management.
Pressure compensated dispensers
Pressure compensated devices can be either laminar or turbulent flow. In both cases, these devices use inlet pressure to change the size, profile or length of the slide path. This modification generally occurs with the deformation, induced by the pressure, of a disc, a diaphragm or the water duct, made of elastomeric material.
Pressure compensated devices are capable of delivering nominal flow over a wide range of inlet pressures, within which delivery is relatively constant. Pressure compensated (self-compensating) regulators can suffer from the drawback that the elastomeric materials they are made of have a tendency to change their properties as they age.
Depending on the material, the elastomer may have a tendency to absorb water, lose elasticity or permanently deform under prolonged tension. The change in the properties of elastomers over time will result in a change in the performance of the device. Recently, drippers with silicone regulating membrane have been introduced. Silicone is a material that does not change over time, does not absorb water, does not lose elasticity and is resistant to chemical agents, thus allowing constant performance over time.
Related topics
- Qualità degli erogatori e coefficiente di variabilità tecnologico
- Curva caratteristica degli erogatori
