Adjustable Drippers
The flow-rate of these drippers can be adjusted according to the changing requirements along the growing season.
The flow-rate of compensated emitters remains uniform provided the available pressure is above a given minimum regulation pressure. There are several compensating mechanisms that narrow or lengthen the internal water passageway when the pressure rises, increasing head losses and keeping the flow rate constant.
Flexible Membrane above Water Path The compensating mechanism is a flexible diaphragm. As the pressure on top of the diaphragm increases it narrows the water passageway below the diaphragm, increasing the head losses and decreasing the flow-rate.
Thread Barb
Fig. 31. Button drippers conector design
Fig. 32. Adjustable dripper (above) and flag dripper (right)
Fig. 34. Button and inline PC drippers
Courtesy "Netafim"
Fig. 33. Flexible diaphragm under pressure
Changing of Water Flow Path Length In another technique, pressure compensation is applied by varying the effective length of the labyrinth. The higher the pressure the longer the effective passageway. This is accomplished by changing the number of openings between a membrane and the labyrinth. These openings are sequentially closed by an increase in the pressure, maintaining the
discharge constant. The shortened water passageway, supported by this technology, decreases clogging hazards and renders an efficient compensating mechanism.
Fig. 36. Change of water passageway length under high pressure - “Mezerplas” ADI PC Dripper Non-Leakage (No Drain) Drippers
Drainage of drip laterals after water shutdown promotes accumulation of precipitates at the bottom of the laterals and in the water passageways within the drippers. It lasts some time after the beginning of irrigation until the laterals are full with water and the required working pressure builds-up. During this time interval, the discharge of the drippers in the initial part of the lateral is significantly higher than that of the drippers at the distal end of the lateral. Frequent small water applications, as in vegetables cropping, makes this time segment a significant fraction of the irrigation time length.
This results in significant difference in water dosage between the initial and the distal ends of the laterals and in the plot as a whole.
The non-leakage drippers keep the lateral full of water after shutdown by sealing the dripper's outlet as the pressure drops. It also facilitates fast pressure build-up in the
laterals at the start of the next irrigation.
Woodpecker Drippers
These drippers are designed for use in plots prone to woodpecker’s damage. The woodpeckers drill holes in the LDPE laterals in search of water. Preventive action is taken by burying the laterals with
the woodpecker drippers underground and connecting thin micro-tubes to the dripper outlet. The distal end of the micro-tube is laid on the soil surface.
Woodpecker damage can also be reduced by distributing water-filled cans in the plot to satisfy the woodpeckers’ thirst.
Fig. 35. ADI PC dripperFrom "Mezerplas" brochure
Bug cover Woodpecker
Fig. 37. Woodpecker drippers
Flap Equipped Drippers
Drippers equipped with a flap on the water outlet prevent the suction of small soil particles into the dripper at shutdown as well as the intrusion of roots into drip lateral installed below the soil surface.
Treflan Impregnated Drippers
For long-term prevention of root intrusion into
subsurface drip laterals, the herbicide Trifluraline (TreflanTM) is impregnated into the drippers during the production process. After installation of subsurface laterals, small amount of the herbicide is released with each water application into the soil around the dripper, sterilizing its immediate vicinity. Drippers containing Trifluraline can substitute routine Treflan application for up to 15 years.
Arrow Drippers
Arrow dippers are used for the irrigation of potted plants. The stick-like dripper is inserted into the bed inside the pot. A high capacity built-in filter and efficient zigzag turbulent water passageway keep the tiny dripper clean and reliable in long-term use.
Multi-Outlet Drippers
Each dripper has 2 – 12 outlets onto which small diameter micro-tubes are connected. These drippers are used mostly in landscaping and potted plants irrigation.
Ultra Low-Volume Drippers
Extremely low water application rates, in the range of 0.1 – 0.3 l/h per dripper, change the water distribution pattern in the soil and the water-to-air ratio in the wetted soil volume. The horizontal movement is more pronounced than with drippers of conventional flow-rate range. Therefore, water can be applied to shallow root systems with minimized drainage beneath the root-zone.
Fig. 38 Flap equipped dripper
Fig. 39. Arrow dripper for greenhouses, nurseries and pot plants Courtesy "Netafim"
Fig. 40 Six outlets
Due to the extremely low water sensitive to clogging because of the narrow water passageways and low flow velocity. There are two technologies to achieve low flow-rate with minimal clogging hazard.
One technology is based on conventional button drippers that emit water into a secondary small
diameter with 10 – 30 molded or inserted micro-drippers. In the second technology, conventional drip laterals are used but the water is applied in pulses created by pulsators or by the irrigation controller. Because of the relatively short pulses and long intervals between them, drippers should be of the non-leakage (no drain) type.
Integral Filtration in Drippers High quality drippers have built-in small integral filters to reduce the clogging hazard of the water passageways and guarantee proper function of the complicated mechanisms needed for pressure compensation, drainage prevention, etc. The filtering area is increased to ensure long-term performance.
Additional anti-clogging means are dual water inlets and outlets in the single dripper and the barbs in on-line drippers which protrude into the lateral so that the water inlet is kept away from the dirt that accumulates on the lateral's walls. Anti-siphon devices such as the above-mentioned flaps also decrease clogging hazard.
Static state Pressure compensation Flushing
Fig. 43. Auto flushing, pressure compensating dripper Courtesy "Netafim"
Auto Flushing Mechanisms
In some of the compensated drippers, a flexible diaphragm is used to release debris that clogs the dripper. When a solid particle blocks the water path, the diaphragm is arched, widens the passageway and releases the clogging object.
Fig. 41. Ultra low flow micro-drippers
Adapted from "Plastro" brochure
Fig, 42. Integral filters Courtesy "Netafim"
Chapter 8. ACCESSORIES
In addition to drippers and pipes, drip irrigation systems are comprised of diverse accessories. Wise selection of these components can guarantee optimal long-term performance of the system.
These accessories can be classified in four categories:
Connectors: connecting pipelines and laterals to the regulating and control devices, interconnecting pipes of different types and diameters, laterals to manifolds and drippers to laterals.
Control, monitoring and regulation devices: valves, filters, water meters, pressure gauges, etc.
Chemicals injectors and safety devices.
Soil moisture measuring and monitoring instrumentation.
Connectors
Connectors are made of metal or plastic materials. They may be two-sided straight-through or angular units, T or Y pattern triple outlets, four-sided crosses or multi-outlet splitters.
Fig, 44. Plastic and metal pipe and lateral connectors
Connectors to control devices are usually threaded or flanged. Connectors between pipes and laterals are mostly barbed or conic. There are simple barb connectors, while more sophisticated connectors have an inner barb and external fastening cap.
HDPE pipes may be joined by heat fusion in the field. If done properly, fusion is reliable and durable.
Control Devices
Valves are basic control devices. There are different types of valves, each of which performs a different task.
Gate valves are used for on-off tasks.
They are not suitable for gradual opening and closing tasks.
Ball valves are also used for on-off tasks.
They have low head losses but are not suitable for flow regulation.
Globe valves have higher head losses but they are efficient and precise for flow regulation.
Angular and Y shaped valves have lower head losses than globe valves and they can also be used for flow regulation.
Butterfly valves have modest head losses and certain throttling capability.
Hydraulic valves appear in most of the before mentioned designs. They have a control chamber in which water pressure from the command line actuates a piston or diaphragm that regulate the flow through the valve by narrowing or expanding the water passageway.
Hydraulic valves are of two types: normally open (N.O.) and normally closed (N.C.).
Normally open (N.O.) valves remain open until the control chamber is filled with water under the system’s pressure, to close it
Normally closed (N.C.) valves remain closed by the water pressure in the main-line.
The closure is secured by a spring, in case of a rupture in the command line. In order to open the hydraulic valve, the controller opens a small valve at the top of the control chamber, releasing the pressure exerted on the diaphragm.
Fig. 45. Lateral start, plugs and lateral end Fig. 46. Reinforced connectors
Fig. 47. Drip laterals connectors and splitters
The pressure which the water in the system exerts on the lower face of the diaphragm reopens the valve.
Normally closed hydraulic valves have higher head losses, but they are safer to use, as the valve remains closed even if the command tube is torn or plugged.
Water meters are essential for accurate water application.
The most prevalent are the Woltmann models. Bi-annual re-calibration is required.
Pressure regulators are used to maintain a constant downstream pressure, independent of upstream fluctuations provided it remains above the regulating pressure.
Pressure regulation is particularly important for drip irrigation.
Thin walled laterals have PN of 4 – 15 m, and burst at higher pressures. When using non-compensated drippers, pressure regulators installed on the manifolds or lateral heads can maintain uniform pressure under harsh topographic conditions.
There are two types of pressure regulators. Simple mechanical devices regulate the pressure against a spring, Fig. 48. Hydraulic valve
Fig. 49. Spring pressure regulator assemblies
Courtesy "Netafim"
while in the more sophisticated devices the pressure is controlled hydraulically by a diaphragm or piston.
Fig. 50. Spring actuated pressure regulator Fig. 51. Hydraulic pressure regulator Metering Valves
The metering valve is a combination of a water meter with a hydraulic valve. The desired volume of water to be applied is dialed in. The valve opens and closes automatically only after the assigned volume has been delivered.
Metering valves are used extensively in drip irrigation. They facilitate also the gradual opening and closing of water, which is important to avoid the collapse of thin-walled laterals. They are handily compatible with automation.
Fig. 52. Horizontal and angular metering valves
The actuator in the metering valve can be a diaphragm or a piston. A diaphragm is less sensitive to dirt in the water, but can be torn in high pressure fluctuations and may wear due to chemical degradation.
Electric Valves
Electric valves are vastly used in automation. They are operated by a solenoid that converts electric pulse to mechanical move. In a small diameter – up to 1” (25 mm) – the solenoid can serve as direct actuator. In wider diameters, the solenoid commands hydraulic actuators. Energy sources are AC current where applicable, batteries and solar cells.
Pressure relief valves have the task to instantly release water under excess pressure in order to protect the system. They can be mechanical, working against a spring (cheaper but less reliable) or hydraulic devices.
Air relief valves are used to release air from the pipelines during filling with water and to let air in when pipelines on slopes drain. Plastic pipes, manufactured to withstand a pressure of 6, 10 or
more bars, are seriously damaged when the pressure inside the pipe falls below atmospheric pressure. “Double action" air relief valves let air escape even when the floating device is lifted by pressure buildup as the pipeline fills with water.
Air Relief Valves and Vacuum Breakers
Fig. 54. Air-relief valves
As mentioned before, air relief valves and atmospheric vacuum breakers are essential components of the drip irrigation system.
There are three types of air relief valves:
Fig. 53. Electric valve "Bermad"
Automatic valve: releases small volumes of air during ordinary operating conditions.
Kinetic valve: releases large volumes of air while the system is filled with water and allows a great volume of air to enter the system at shutdown.
Combination valves: Automatic and kinetic valves mounted together in one assembly.
Atmospheric vacuum breakers are small devices, ½” – 1” in diameter that break the vacuum at water shutdown and do not allow air to escape from the system when water drains from the irrigation system and the pressure in the pipelines falls below the atmospheric pressure.
Air relief valves introduce air into the
irrigation system when its pressure equals or falls below the atmospheric pressure and function as vacuum breakers.
Check-Valves and Backflow Preventers
These valves are used to prevent backflow from the irrigation network to the water supply network, when that network supplies potable water to consumers. These devices are described in the chapter on fertigation.
Lateral-End Flush Devices
In drip irrigation, a vast amount of precipitates is accumulated in the lateral distal end.
The automatic lateral end flush device releases water at the start of irrigation, before working pressure builds-up in the system. This performs routine flushing of the laterals, eliminating the need to do it manually.
Fig. 55. Atmospheric vacuum breakers
Fig. 56. Lateral-end flushing action
Chapter 9. FILTRATION
Due to the narrow water passageways and low water-flow velocity in the drippers, drip systems are sensitive to clogging. Clogging prevention requires high-level filtration and complimentary chemical and physical water treatments.
Table 12. Characteristics of water passages in drippers (example)
Water passageway Water passageway
Flow
* In non-compensated drippers – nominal flow rate at 1 bar (10 m) pressure head. Courtesy “Netafim”
Impurities in water can be classified in four categories:
Inorganic suspended solids: sand, silt, clay and gravel.
Dissolved chemicals that precipitate from the water in certain circumstances. The most prevalent chemical precipitates are calcium carbonate, calcium phosphates and calcium sulfate (gypsum). Dissolved iron and hydrogen sulfide enhance development of bacteria population that clogs drippers, filtering media and command micro-tubes.
Live organic material: zooplankton and phytoplankton - algae, protozoa, bacteria and fungi. Live organisms can propagate rapidly in suitable conditions and excrete sticky mucus material with enormous clogging potency.
Organic debris
The most contaminated waters are raw sewage and low-quality reclaimed water.
Water pumped from ponds, lakes, rivers, streams, canals and dam reservoirs, also contains a high load of impurities. Water pumped from sand aquifers contains a relatively high amount of suspended sand.
There are diverse filtering methods using different filtering media: screens, grooved discs, gravel and sand. Sand and silt separation is often performed as a pre-treatment in settling ponds and tanks or by means of centrifugal separators. In greenhouses with detached growing media, in which drainage water is recycled for reuse in irrigation, slow sand filter systems are used to eliminate water-borne pathogens.
Screen (Strainer) Filters
There are different types of screen filters. The most important properties of a screen filter are filtration degree, filtration surface area and filtration ratio.
Filtration degree is defined with two systems of units: microns and mesh number. The filtration degree in microns designates the diameter of the biggest ball-shaped particle that can pass between the screen wires. The mesh number counts the number of wires along 1" (25.4 mm) length of the screen. The two definition procedures are not fully inter-convertable. Holes width may differ in two screens with the same mesh number due to a difference in wire thickness. Rough conversion from one system to another is made using the rule of thumb: mesh number x microns = 15,000.
When selecting the filtration degree, both the dimensions of the water passageways in the dripper and the character of water impurities should be considered. When the impurities are suspended
inorganic solids (sand, silt, chemical precipitates), the maximum perforation diameter should be 25%-30%
of the width of the emitter’s narrowest water passageway. When the impurities are organic and biological materials, the maximum perforation diameter should be no more than 10%-20% of the water passageway width. Screen filters are most suitable for water with inorganic impurities, while high loads of organic and biological impurities may quickly clog the screen.
Fig. 58. Head losses in clean screen filters Adapted from "Odis" brochure
One of the main disadvantages of screen filters is the fast accumulation of dirt on the screen's surface. The accumulated dirt increases the head losses and may cause the
Fig. 57. Screen filter
collapse of the screen. Excess dirt accumulation should be prevented by monitoring the pressure difference between the filter inlet and outlet and cleaning the screen when the difference is greater than 5 m head.
Disc Filters
Disc filters are the favored choice for filtration of water containing mixed impurities - inorganic solid particles and organic debris. The casing is made of metal or plastic materials. The filtering element is made of a stack of grooved rings, tightened firmly by a screwed cap or a spring with a water-piston. Water is filtered as it flows through the grooves. The intersections of the grooves provide in-depth filtering. Coarse particles are trapped on the external surface of the stack. Finer particles and organic debris remain in the inner grooves. The disc filter has a significantly higher dirt-retention capacity than screen filters. The definition of the filtration degree is identical to that of screen filters and is mostly indicated by the color of the discs.
Fig. 59. Disc filter Media Filters
Media filters are used to protect the drippers when using water with a high organic load from open water bodies or reclaimed water. Wide-body (0.5 - 1.25 m in diameter) media containers are made of epoxy-coated carbon steel, stainless steel or fiberglass.
The filtering media are 1.5 - 4 size mm basalt, gravel, crushed granite particles or fine silica sand. The organic impurities adhere to the surface of the media particles. The accumulated dirt should be back-flushed routinely in order to eliminate excessive head losses. The filtration degree is defined according to that of screen and disc filters.
Sand Separators
High loads of sand and other solid particles should be removed before reaching the main filtration system.
Table 14. Sand particle size and mesh equivalent Sand No. Effective sand
Crushed Silica 20 0.28 170 - 230
Fig. 60. Media filter
There are two methods of sand separation.
The traditional practice is based on sedimentation of solid particles from the water by slowing down its flow in settling tanks or basins. Closed tanks conserve the water head while the use of open settling basins requires re-pumping of the treated water into the irrigation system.
Contemporary technology employs centrifugal sand separators that sediment sand and other suspended particles that are heavier than water by means of the centrifugal force created by the tangential flow of water into a conical container. The sand particles are thrown against the walls of the container by the centrifugal force,
Contemporary technology employs centrifugal sand separators that sediment sand and other suspended particles that are heavier than water by means of the centrifugal force created by the tangential flow of water into a conical container. The sand particles are thrown against the walls of the container by the centrifugal force,