Irrigation drippers (also called emitters) are the most critical segments in the drip irrigation system. The function of all drippers is to control the flow of water from the inner, pressurized side of the pipe into the atmospheric pressure outside the pipe. The aim is to make this outflow uniform to all plants in the field, regardless of their location or the terrain conditions.
Typically, drip irrigation system products are divided into several families. Each product family has unique features that make it advantageous for specific types of uses.
Drippers are assified according to several parameters:
1. Dripper shape
Cylindrical drippers are the veteran workhorses of the dripper range. These drippers have a massive body, large filters, long and a wide labyrinth, and the PC version has a very large, elastic diaphragm. Two outlets on opposite sides of the pipe ensure that regardless of pipe position, at least one side will always be open and free from sediments.
Cylindrical driplines are typically installed in orchards and landscape systems.
Their ability to sustain challenging water quality and fertilizer sediments, and their physical robustness make cylindrical drippers a long-term investment. On the downside, cylindrical drippers require more material for production and are bulkier for logistics in drip irrigation systems. Inside the pipes, the profiles of cylindrical drippers increase head loss, compared to low, flat drippers (larger Kd).
Flat drippers are more economical as far as production, shipment and logistics, requiring less production material and more compact reels.
Flat drippers have a modest profile in the pipe (smaller Kd) and therefore allow longer length of laterals and more drippers per meter. In the field, the compact dripline reels allow easier logistics, faster installation and faster retrieval when irrigation season is over in seasonal crops.
2. Flow rate regulations
The second parameter is all about flow rate regulations (PC or Non-PC Drippers for drip irrigation systems).
Turbulent Flow Drippers:
The turbulent flow dripper has an internal water path that looks like a labyrinth. While water flows through the “teeth” of the labyrinth, the flow becomes turbulent and the water loses energy and pressure. Dimensions of the labyrinth and the internal water pressure dictate the level of turbulence and the consequent dripper flow rate.
When running a drip irrigation stsyem on a flat terrain, pressure in the pipe declines along the driplines. As a result, the flow rate of the first dripper is higher than the last. For shorter rows, this difference is marginal, but on long rows, the difference will produce uneven water distribution to an extent that may affect the uniformity of crop growth. On undulated land or steep slopes, the difference in flow rate may be even bigger, further restricting the allowable length of dripline laterals.
Pressure Compensated (PC) (Flow regulated drip irrigation system):
PC drippers are designed to overcome the limitations of Turbulent Flow drippers by regulating the water pressure, thus unifying the flow rate along the line.
PC drippers are designed with a flexible membrane that controls the dripper’s flow rate. The membrane functions as a tiny pressure sustaining valve: when the pressure in the pipe rises or falls, the dripper flow rate remains unchanged, therefore the first and the last drippers in a long row will emit the same flow rate. Similarly, on steep slopes, all drippers will have a unified flow regardless of their uphill or downhill position.
In advanced PC drippers, a unique design regulates the flow by pressing on the labyrinth. When irrigation starts or stops, the gap between the membrane and the labyrinth opens wide, flushing sediments from the line.
3. Advanced solutions for running a drip irrigation system:
The pressure compensation mechanism initiated the development of these two types of drippers for special applications:
Non-Drain application for pulse irrigation:
In a regular dripline, when water flow ceases, most of the water will drain from the pipe through the drippers in the lowest part of the dripline. When irrigation starts again, the entire dripline will have to be filled again before the drippers all have a uniform flow rate.
Pulse irrigation is an irrigation management method whereby irrigation is applied numerous times a day for very short periods. This method eliminates water stress from the plants and promotes very fast growth. If a “regular” dripline is used for pulse irrigation, lower drippers in the dripline will emit considerably more water than the elevated drippers.
However, with non-drain PC drippers, the dripline remains full of water between applications ensuring optimal uniformity along the line. When the dripline is full, the extra time required for filling the pipe at the beginning of the pulse is eliminated, enabling very short pulses as required.
Anti- Siphon for subsurface dripline insertion (SDI drip irrigation system):
When an irrigation cycle is finished, water drains from the dripline and air penetrates the tubes. However, when the driplines are installed under the ground, soil particles may invade the drippers through the outlets. Anti-Siphon technology allows the drippers to drain, but very slowly, enabling water to percolate slowly from the dripper, and air to replace the water volume. This advanced solution eliminates soil suction into the drippers.
Read more about SDI in Root -Guard Technology.