STATE OF ISRAEL
MINISTRY OF FOREIGN AFFAIRS
CENTRE FOR INTERNATIONAL
MINISTRY OF AGRICULTURE AND RURAL DEVELOPMENT
CENTRE FOR INTERNATIONAL AGRICULTURAL DEVELOPMENT
Irrigation Consultant and Former Director,
Irrigation and Soil Field Service
Chapter Topic Page
List of Tables II
List of Figures III
Foreword to The First Edition VIII
Foreword to the Second Edition IX
1. Introduction 1
The History of Drip Irrigation 1
2. Principles of Drip Irrigation 4
Advantages and Limitations 5
3. The Distribution of Water in The Soil 8
4. The Drip System 14
5. Flow Rate – Pressure Relationship 18
6. Pipes and Tubes for Drip Irrigation 28
7. Dripper Types, Structure, Function and Properties 32
8. Accessories 40
9. Filtration 46
10. Fertigation 58
11. Water Quality 64
12. Monitoring and Control 71
13. Subsurface Drip Irrigation (SDI) 74
14. Family Drip Irrigation 80
15. Water Distribution Uniformity 82
16. Drip Irrigation of Crops 84
17. Basics of Drip System Design 93
18. Drip Irrigation Scheduling 106
19. Maintenance 112
20. References and Bibliography 116
Conversion factors 120
LIST OF TABLES
1. Pressure Units 18
2. The Friction Coefficient ( C ) of Pipes 20
3. The Effect of Dripper Exponent on Head-Loss – Flow-
4. Head losses in Acuanet automatic valve 23
5. Plastro Hydrodrip II Integral Drip Laterals Technical
6. PE Pipes for Agriculture 29
7. Internal Diameter and Wall Thickness of LDPE Pipes 29
8. Internal Diameter and Wall Thickness of HDPE Pipes 30
9. PVC Pipes for Agriculture 30
10. Internal Diameter and Wall Thickness of PVC Pipes 31
11. Flow-Rate of Spring Actuated Pressure Regulators 42
12. Characteristics of Water Passageways in Drippers
13. Screen Perforation - examples 47
14. Sand particle size and mesh equivalent 48
15. Nominal Filter Capacity – examples 50
16. Relative Clogging Potential of Irrigation Water in Drip
17. Threshold and Slope of Salinity Impact on Yield 67
18. Yield Increase and Water Saving in Conversion From
Surface to Drip Irrigation
19. Manufacturer Data about the Allowed Lateral Length in
the Examined Alternatives
20 Allowed lateral length of Ram 16 PC drippers 97
21. Calculation Form: Head losses in pipes 101
22. Head Loss Calculation Form – Pressure Compensated
23. Head Loss Calculation 105
24. Irrigation Scheduling – Calculation Form (example) 106
25. Irrigation Scheduling Form for Annuals 109
26. Operative Irrigation Schedule 111
LIST OF FIGURES
1. Clay pot 1
2. Early patents issued for drip irrigation 2
3. Wetting pattern of drip irrigation in different soil textures 4
4. Water distribution in the soil along time 8
5. Water distribution from a single dripper in loamy and sandy soil 9
6. Salt distribution in the wetted volume 10
7. Leaching of salt into the active root-zone by rain 10
8. Diverse root systems 12
9. Typical root systems of field crops 13
10. Root system in drip irrigation vs. root system in sprinkler irrigation 13
11. Simplified scheme of drip system 14
12. Typical layout of drip irrigation system 15
13. Components of drip irrigation system 16
14. Control Head 17
15. Relationship between the dripper exponent and lateral length 22
16. Pressure Compensated dripper flow-pressure relationship 23
17. Non-pressure compensated flow-pressure relationship 23
18. Acuanet automatic valve 24
19. Head loss nomogram, based on Hazen-Williams formula 25
20. Nomogram for calculation of head losses in HDPE pipes 26
21. Nomogram for calculation of head losses in LDPE pipes 27
22. Evolution of the passageway style 32
23. Turbulent flow 33
24. Orifice dripper 33
25. Vortex dripper 33
26. Labyrinth button dripper 33
27. Tape dripper lateral: empty and filled with water 33
28. Point-source and line-source wetting by drippers 34
29. In-line laminar dripper and turbulent dripper 35
30. On-line drippers 35
31. Button drippers insert design 36
LIST OF FIGURES (Continued)
32. Adjustable and flag drippers 36
33. Flexible diaphragm under pressure 36
34. Button and inline PC drippers 36
35. ADI PC dripper 37
36. Change of water passageway length under high pressure 37
37. Woodpecker drippers 37
38. Flap equipped dripper 38
39. Arrow dripper for greenhouses, nurseries and pot plants 38
40. Six outlets 38
41. Ultra low flow micro-drippers 39
42. Integral filters 39
43. Auto flushing, pressure compensating dripper 39
44. Plastic and metal pipe and lateral connectors 40
45. Lateral start, plugs and lateral end 41
46. Reinforced connectors 41
47. Drip laterals connectors and splitters 41
48. Hydraulic valve 42
49. Spring pressure regulator assemblies 42
50. Spring actuated pressure regulator 43
51. Hydraulic pressure regulator 43
52. Horizontal and angular metering valves 43
53. Electric valve 44
54. Air-relief valves 44
55. Atmospheric vacuum breakers 45
56. Lateral-end flushing action 45
57. Screen filter 47
58. Head losses in clean screen filters 47
59. Disc filter 48
60. Media filter 48
61. Sand separator 49
LIST OF FIGURES (Continued)
62. Hydro-cyclone sand separator – head losses and optimal flow rates 49
63. Self-flushing screen filter 52
64. Automatic flushing of disk filters 52
65. High capacity media filters array 53
66. Back-flushing of media filters 53
67. High capcity automatic filter 53
68. Compact automatic filter 54
69. Slow sand filter 55
70. Slow sand filter scheme 56
71. Treflan impregnated disk stack 57
72. Fertilizer tank 58
73. Venturi injector 59
74. Piston and diaphragm hydraulic pumps 59
75. No-drain hydraulic pump 59
76. Mixer 60
77. Electric pump 60
78. Check valve 63
79. Tandem backflow preventer - exploded 63
80. Tandem backflow preventer 63
81. Installed backflow preventer 63
82. Chlorine- distribution below and between drippers 68
83. Salt level in relation to distance from dripper 68
84. Water quality for irrigation 68
85. Tensiometers 71
86. Soil moisture capacitance sensor 71
87. Multi-factor simultaneous phytomonitoring 72
88. Scheme of SDI system 74
89. Wetting pattern in SDI 77
90. Burying SDI lateral 78
91. Three-shank SDI lateral burying machine 79
92. Bucket kit 80
LIST OF FIGURES (Continued)
93. Drum kit 80
94. "Netafim" Family Drip System (FDS) 81
95. Components of Family Drip System (FDS) 81
96. Treadle pump 81
97. Apple root system in well aerated soil 84
98. Apple root system in compact soil 84
99. Drip irrigation Layouts in orchards 85
100. Drip laterals in vineyard, hung on the trellis wire 85
101. Dripper layouts in pecan orchard 85
102. Typical shoot and fruit growth curves for peach and pear 86
103. Partial Root-zone Drying with two laterals per row 87
104. Mango grown on nutrition ditches vs. control 87
105. Mechanized deployment of drip laterals 88
106. Cotton root development 88
107. Laterals on top of hillocks in potatoes 89
108. Lateral between hillocks 89
109. Potatoes – one lateral per row 89
110. Wide-scale drip irrigation in greenhouses 91
111. Drip irrigation of potted plants in greenhouse 92
112. Roadside drip irrigation 92
113. Wetted volume in different soil types 94
114. Apple orchard map 95
115. Local head losses in accessories 98
116. Drip system layout scheme 99
117. Feasible layouts 100
118. Segmented drawing for head loss calculation 101
119. The chosen diameter for mainline and manifold 102
120. One manifold layout 103
121. Pressure compensated Ram 2.3 l/h dripper, one shift design 104
122. Melons plot map 104
123. Melons – In-line non-compensated drippers 105
LIST OF FIGURES (Continued)
124. Schematic wetting pattern in different textured soils 107
125. Different schedules of drip irrigation operation 108
126. Layout of drip system for 55 ha. Of cotton 110
127. Automatic line flushing valve 114
128. Punch and holder 115
FOREWORD TO THE FIRST EDITION
The need for a comprehensive and updated book on Drip Irrigation has long been felt
as reflected by the intensive scheduling of international irrigation courses in
CINADCO’s yearly training program. The booklet on Drip Irrigation written by
Elimelech Sapir, and the late Micha Shani, in 1976 was updated in the early 1990s
and is used extensively in CINADCO’s irrigation training courses, in Israel and
abroad. However, with the rapid expansion and technological advances of Israeli
irrigation equipment, it became apparent that more detailed and systematic literature
Moshe Sne, the former Director of the Irrigation and Soil Field Service of the Israeli
Ministry of Agriculture and Rural Development, Extension Service, has been greatly
involved in the subject of irrigation systems and techniques in general, and drip
irrigation in particular, for many years. He has also served as the chief irrigation
course adviser for CINADCO. On the eve of his retirement from government service,
he committed himself to the worthy task of preparing a book on Drip Irrigation in
We wish to thank the author for the great amount of work and effort he put into the
writing and compilation of the drip irrigation subject matter presented here. He was
greatly assisted by the leading irrigation companies in Israel who allowed the use of
pictures, charts, diagrams and figures. We wish to thank them and the many
professionals who assisted Mr. Sne in this project and are credited throughout the
We are happy to share the professional material presented here with irrigation
experts, agriculturalists and others in the field, in countries throughout the world that
participate in Israel’s international cooperation programs. The contents have been
formulated particularly for the physical conditions prevailing in Israel. These are
recommendations only and should not take the place of local detailed irrigation
This is the first edition of Drip Irrigation printed in a limited number of copies. We
would appreciate your comments and suggestions for the coming editions.
Abraham Edery, Director of Training, CINADCO
Shirley Oren, Publications’ Coordinator, CINADCO
FOREWORD TO THE SECOND EDITION
A year has passed since the publication of the First Edition of Drip Irrigation written
by Moshe Sne. At the time of the first printing, we requested from the irrigation
experts, irrigation course participants and others who would be reading the book to
give us their comments and suggestions.
This was done and the author incorporated the comments and suggestions received,
as well as his own changes and corrections into this publication.
We are pleased to bring to print in May 2005 the second edition of Drip Irrigation. We
are greatly appreciative of the efforts made by Moshe Sne to improve upon and
correct the already comprehensive material he compiled previously.
As we mentioned in the Foreword to the First Edition, we are happy to share this
professional material with irrigation experts, agriculturalists and other interested
parties in countries throughout the world that participate in Israel's international
agricultural development programs. In order to facilitate this purpose, the book is
currently being translated into Spanish and Russian. The content has been
formulated particularly for the physical conditions prevailing in Israel. These are
recommendations only and should not take the place of local detailed irrigation
Abraham Edery, Director of Training, CINADCO
Shirley Oren, Publications' Coordinator, CINADCO
I would like to thank my colleagues and friends, as well as the Irrigation course 2004
participants for proofreading the preliminary first edition and for the helpful remarks
and corrections. Their valuable contribution had been embedded in the current
Second Edition of the publication being printed in 2005.
I am deeply grateful to the authors of the books and papers cited in the Reference
List and the Bibliography. The vast material on drip irrigation inspired me and filled
me with admiration for the enthusiastic and hard-working people in the forefront of
irrigation technology. I would also like to thank the manufacturers for the wealth of
information embodied in their brochures and professional guides. I am particularly
grateful to Mr. Nachman Karu and Mr. Dubi Segal for their contribution of impressive
and useful graphic material.
Last but not least, thanks to Ms. Shirley Oren and Ms. Bernice Keren for their patient
editing and elaboration of the Second Edition of Drip Irrigation.
In the first version, uploaded to Scribd on September 19, some mishaps occurred
during the conversion from the print to the electronic version, mostly in matching
between the table of contents, and the actual document layout. These discrepancies
had been adjusted. Additionally, replacement of some outdated figures and minor
corrections and adjustments had been done in this version of the document.
Chapter 1. INTRODUCTION
Drip irrigation, by definition, is an irrigation technology. However, during the last four
decades, since the start of its world-wide dissemination during the early sixties, it
appeared not only as an irrigation technology but as a comprehensive agro
technology that changed crop growing practices and widened modern agricultural
horizons. Drip irrigation facilitated increased efficiency of water use in irrigation and
triggered the introduction and development of fertigation – the integrated application
of water and nutrients. It raised the upper threshold of brackish water use in irrigation
and simplified the harmonization of irrigation with other farming activities. Drip
irrigation facilitated optimal “spoon-feeding” of water and nutrients to crops, attuned
to the changing requirements along the growing season. Drip irrigation enabled the
accurate supply of water and nutrients to the active root-zone with minimal losses. In
protected cropping, it facilitated the combination of the advantages of hydroponics
with improved plant support by solid detached media. Drip irrigation has promoted
the sophistication of monitoring, automation and control of irrigation, as well as the
diversification of filtration technology. Drip irrigation has gained momentum during the
last two decades. The world-wide area under drip irrigation is estimated at 3 million
ha., out of a total area of 25-30 million ha. irrigated with pressurized irrigation
technologies. The area of surface irrigation is estimated at 270-280 million ha.
THE HISTORY OF DRIP IRRIGATION
From the early days of irrigated agriculture, farmers and irrigation professionals
looked after concepts and technologies to improve water utilization in agriculture.
One of these concepts was the localized application of water directly to the root zone.
Another concept was subsurface water application to avoid evaporation from the soil
Such technology was used by the ancient
Persians and is still applied in some countries in
Asia and Africa. Clay pots made of unglazed
indigenous earth-ware have many micro-pores in
their walls. These micro-pores do not allow water
to flow freely from the pot, but slowly release the
water in the direction in which suction develops by
the tension gradient. The pots are buried neck-
deep into the ground, filled with water and the
plants are planted next to them.
In south-east Asia, bamboo drip irrigation has been in use for more than 200 years.
Stream and spring water was tapped into bamboo pipes in order to irrigate
plantations. About 18-20 l/min of water that enters the bamboo pipe system flows
along several hundred meters and is finally distributed to each plant at a rate of 20-
80 drops per minute. This traditional system is still in use by tribal farmers to drip-
irrigate their black pepper plots.
The concept of water saving was further elaborated during the nineteenth century.
People involved with irrigation were dissatisfied with the wasteful surface irrigation
technologies. There is evidence that in 1860, subsurface tile pipes were used
experimentally for irrigation in Europe. Patents for water saving irrigation
technologies were registered in Europe and the United States. Patent # US146,572
dated January 20, 1874 by Nehemiah Clark of Sacramento, California, describes a
Fig. 1. Clay pot
pipe with a "non-clogging" leaking connection. In the year 1888, Mr. Haines of
Nashville, Iowa, registered a patent of the direct application of water to the root
system of orchard trees. In 1917, Dr. Lester Kellar introduced an agricultural drip
system in a symposium at Riverside, CA., but further development of drip irrigation in
the United States was delayed for another 40 years.
Perforated pipes for subsurface irrigation were used experimentally in Germany in
1920 and in the USSR in 1923. In 1926, Mr. Nelson of Tekoa, Washington, had
registered a patent for a subsurface irrigation system. Another subsurface irrigation
system was examined in 1934 at the New Jersey and Indiana Agricultural
Experiment Stations. After WWII, micro-tubes were used for greenhouse irrigation in
England and France. In 1954, Mr. Richard Chapin developed in the USA, drippers for
irrigation of potted plants in greenhouse. Mr. Hansen, of Denmark, developed a small
plastic tube for the irrigation of potted plants in greenhouses.
Fig. 2. Early patents issued for drip irrigation
The breakthrough in drip irrigation occurred in the early sixties, firstly in Israel and
later in the United States. This initiative is attributed to Mr. Simcha Blass, who
invented a dripper with long laminar water flow passageways in the form of a spiral
micro-tube. The micro-tube was first wrapped around the feeding lateral, followed by
an improved model comprised of a molded coupling with a built-in spiral. Later it was
manufactured as a two-piece in-line dripper (US patent 3,420,064).
Mr. Blass collaborated with Kibbutz Hazerim to establish "Netafim", a worldwide
leading drip irrigation company. At the same era another Israeli inventor, Mr. Ephraim
Luz developed a different drip irrigation system, with perforated polyethylene tubes, 4
– 6 mm in diameter. In both technologies the drip laterals were buried 20 – 40 cm
below the soil surface. The main flaw with the buried laterals was the clogging of the
drippers by soil particles and intruding roots. Mr. Yehuda Zohar, an agricultural field-
adviser demonstrated that on-surface drip irrigation had the same advantages as the
subsurface installation but with significantly less clogging hazard. For many years the
on-surface pattern was the dominant drip irrigation technology. During the late sixties
and early seventies, "Netafim" licensed some foreign factories of irrigation equipment
in the USA and South Africa to manufacture its patented drippers.
As mentioned before, in 1954, Mr. Richard Chapin of the United States developed a
system comprised of small diameters tubes for irrigation of pot plants in
greenhouses. In 1964, he invented a drip tape for the irrigation of cantaloupes. In
1974, he developed the bucket kit for irrigation of small family plots in developing
countries. That system does not require an external source of energy.
In 1962, Mr. S. Davis installed an experimental subsurface drip irrigation system in a
lemon orchard in Pomona, California, USA. Only ten years later, during the early
seventies, after the problems of root intrusion and soil particle suction had been
resolved, did the installation of subsurface drip irrigation (SDI) systems expand on a
wide scale in California and other States of the United States.
Hawaiian sugar producers were introduced to drip irrigation In 1970, at an agricultural
convention in Israel. Returning to Hawaii, they converted a significant portion of sugar
cane acreage to drip irrigation, with astounding achievements in both water savings
and sugar content.
In order to reduce the costs of the drip system, perforated thin-wall tapes were
introduced. However the variance in flow-rate and the clogging of the outlets were
unacceptable. These problems were solved with the introduction of a twin-walled
tape in which an inner conveyance tube bled water into a second outer distribution
duct that emitted water from tiny holes onto the ground at low flow rates. A ratio of
four outlet holes for every inner hole rendered low-flow rates with acceptable
Corresponding with the expansion of drip irrigation in the early sixties, fertigation
technology evolved. Due to the small volume of wetted soil in drip irrigation, an
adequate supply of nutrients to the root system requires the synchronization of water
and nutrient supply through the drip system.
Further steps in the development of drip irrigation technology was the introduction of
seep hoses, woodpecker drippers, compensated drippers, non-leaking (no-drain)
drippers, anti-siphon mechanisms and techniques that prevent root intrusion.
Drip irrigation triggered the development of filtration systems and chemical water
treatment technologies that were necessary to protect the narrow dripper water
passageways from clogging. Sophisticated control and monitoring instrumentation
has been developed to enable the optimal implementation of this technology.
Drip irrigation was also adopted by gardeners and landscape architects. It
revolutionized the concept of irrigation in gardening, with its capability to irrigate
without disturbing visitors. The utilization of reclaimed water with subsurface
installation and the convenience of irrigating narrow strips of vegetation without
wetting sidewalks, excited leading professionals in this sector. Nowadays there are
many countries where sales of drip irrigation equipment for landscaping and
gardening applications surpass those of agricultural applications.
Mainstream drip irrigation is relatively expensive and is actually unaffordable for low
income farmers in developing countries. This impediment has been partially solved
by local production of cheap low-quality drip equipment, which compromises on
emission uniformity and life expectancy. Another solution was the development of
simple drip kits, such as the bucket and drum kits, designed for small family-run
Chapter 2. PRINCIPLES OF DRIP IRRIGATION
Drip irrigation, sprinkler irrigation, center pivot and lateral-move are classified as
pressurized irrigation technologies. In pressurized irrigation, the driving force of water
movement is provided by an external energy source (or a raised reservoir). The water
is delivered through a closed pipe system. This differs from surface irrigation
technologies – flood, border, furrow and small basin irrigation – in which the driving
force of water flow is gravity, and the delivery and application structures – canals,
ditches, furrows, small ponds and basins – are open to the atmosphere.
Drip irrigation is a section of the micro-irrigation (localized irrigation) sector, which
includes also micro-sprayers and mini-sprinklers. The term trickle irrigation is
generally used to describe irrigation methods whereby small quantities of water are
applied at short intervals directly to the soil, from point source discrete emitters
spaced along thin tubes or tapes, line-source densely mounted dripper outlets, or
seep-hoses. Water applied from small sprayers, micro-sprinklers and bubblers is
transmitted to the soil through the atmosphere. The terms trickle, micro, drip, low
volume and localized irrigation are sometimes used interchangeably in the literature,
although each one has a slightly different technical meaning.
With micro-irrigation, the emitters deliver water through three different types of
emitters: drippers, bubblers and sprayers/micro-sprinklers. Drippers apply water as
discrete droplets or trickles. With bubblers, water ‘bubbles out’ from the emitters at
higher flow rates and the flow appears as a continuous stream. Micro-sprinklers
sprinkle, spray or mist water to the atmosphere around the emitters.
The uniqueness of drip irrigation is the partial wetting of the soil. Water is applied by
many tiny emitters, 5,000 – 300,000 per hectare. In on-surface installation, each
emitter moistens the adjacent surface area. The percentage of the wetted surface
area and soil volume depends on soil properties, initial moisture level of the soil, the
applied water volume and emitter flow rate. In subsurface installation, the soil surface
Fig. 3. Wetting pattern of drip irrigation in different soil textures
Adapted from: The University of Maine Cooperative Extension Farm Note
The lateral movement of the water beneath the surface of a medium or heavy
textured soil is more pronounced than in sandy soils. Whenever the dripper's flow
rate exceeds the soil intake (infiltration) rate and its hydraulic conductivity, the water
ponds on the soil surface and wets larger soil volume.
The vertical cross section of the wetted volume in sandy soils resembles a carrot. In
medium textured soil, the dimensions of the wetting depth and wetted diameter are
similar, while in heavy soils the horizontal dimension of the wetted volume is greater
than that of the wetted depth.
Indicative values for the wetted diameter by a single dripper may be 30 cm in a light
soil, 60 cm in a medium soil and 120 cm in a fine textured soil.
Due to the partial wetting of the soil in drip irrigation, water has to be applied more
frequently than with other irrigation methods that wet the entire area such as sprinkler
and flood irrigation.
The capacity to apply water to each plant separately in small, frequent and accurate
dosing enables high application efficiency. Water is delivered from the emitter
continuously in drops at one point, infiltrates into the soil and wets the root zone
vertically by gravity and horizontally due to capillarity.
During the last three decades, subsurface drip irrigation (SDI) has gained
momentum. The wetting pattern with SDI is somewhat different from that obtained
with on-surface emitters.
The localized and limited wetting pattern by drip systems requires the application of
fertilizers through the drip system, a technique named fertigation.
The great number of water emitters per unit area requires the minimization of the
single emitter’s flow-rate (discharge). The customary dripper flow-rate range is 0.1 –
8 liter per hour (l/h). The low emitter flow-rate is achieved by diverse designs: a tiny
orifice, large head losses within a long flow path, turbulent or vortex flow.
The narrow passageways in the emitters and the low flow rates lead to the
accumulation and precipitation of substances that may fully or partially clog the
system. Adequate filtration is a prerequisite for the implementation of drip irrigation.
Complementary chemical treatments are required when low quality water is used for
ADVANTAGES AND LIMITATIONS OF DRIP IRRIGATION
Drip irrigation technology has many advantages over other irrigation technologies.
Drip irrigation significantly increases the efficiency of water utilization and improves
the growing conditions of the irrigated crops.
• Accurate localized water application: Water is applied precisely to a
restricted soil volume, corresponding with the distribution of the root system.
Appropriate water management can minimize water and nutrient losses
beneath the root-zone.
• Minimization of evaporation losses: The reduced wetted upper surface area
decreases water losses by direct evaporation from soil surface.
• Elimination of water losses at the plot's margins: with drip irrigation, water
does not flow beyond the limits of the irrigated plot as happens with sprinkler
irrigation. The drip system can actually fit any plot, regardless of shape, size or
• Decrease in weed infestation: The limited wetted area decreases the
germination and development of weeds.
• Desirable air-water equilibrium: The soil volume wetted by drip irrigation
usually retains more air than a soil that is irrigated by sprinkler or flood
• Simultaneous application of water and nutrients: Application of nutrients
together with the irrigation water directly to the wetted soil volume, decreases
nutrient losses, improves nutrient availability and saves the labor and/or
machinery required for the application of fertilizers.
• Adjustment of water and nutrient supply to changing crop demand along
the growing season: Fertigation technology together with high frequency
water and nutrient applications facilitate the tuning of the supply to the
dynamic requirements of the crop.
• Automation: Automatic controllers can easily be incorporated in drip irrigation
• Adaptability to harsh topographical and soil conditions: Drip irrigation
functions successfully on steep slopes, shallow and compacted soils with low
water infiltration rate and sandy soils with low water-holding capacity.
• Irrigation does not interfere with other farming activities: The partial
wetting of the soil surface does not interfere with other activities in the plot,
such as spraying, fruit thinning and harvesting.
• Water distribution is not disturbed by wind: Drip irrigation can proceed
under windy conditions. Wind does not interfere with drip irrigation, unlike in
• Low energy requirements: Due to the low working pressure, energy
consumption in drip irrigation is significantly lower than that of other
pressurized irrigation technologies such as sprinkler and mechanized irrigation
• Decrease in fungal leaf and fruit diseases: Drip irrigation does not wet the
plant's canopy. This reduces the incidence of leaf and fruit fungal diseases.
• Avoiding leaf burns: The elimination of foliage wetting reduces leaf burns by
salt and fertilizers present in the irrigation water.
• Allows for extended use of brackish water for irrigation: Frequent
watering with drip irrigation allows for the use of irrigation waters containing a
relatively high concentration of salt with minor impact on plant development
and yield. The frequent applications dilute the salt concentration in the soil
solution beneath the emitter and drive the salt to the margins of the wetted soil
Due to the limited wetted soil volume, the narrow water passageways in the emitters
and the vast amount of equipment needed, drip irrigation has some drawbacks.
• Clogging hazard: The narrow passageways in the emitters are susceptible to
clogging by solid particles, suspended organic matter and chemical
precipitates formed in the water. Clogging may also occur by suction of soil
particles and root intrusion into the dripper.
• High initial cost: Due to the large amount of laterals and emitters, mobility of
drip systems during the cropping season is rarely feasible. Most systems are
solid-set arrays, resulting in high cost of equipment per area unit.
• Salt accumulation on the soil's surface: Upward capillary movement of
water from the wetted soil volume and evaporation from the soil's-surface
leave behind a high concentration of salts in the upper soil layer. Light rains in
the beginning of the rainy season, leach the accumulated salts into the active
root zone and may cause salinity damage to the crop.
• Vulnerability of on-surface laterals and drippers to damage by animals:
The laterals, particularly the thin-walled tapes and the tiny drippers are prone
to damage by rodents, rats, moles, wild pigs and woodpeckers. Subsurface
laterals and drippers may be also damaged by rodents.
• Negligible influence on microclimate: Irrigation is occasionally used to
improve local climate conditions – reducing temperature during heat spells
and rising the temperature during frost events. With sprinkler and sprayer
irrigation, a fraction of the sprinkled water evaporates, releasing energy to the
atmosphere in cold weather and absorbing heat in hot weather. Naturally, this
does not occur with drip irrigation
• Restricted root volume: The frequent water applications to limited soil
volume lead to the development of restricted and sometimes shallow root
systems. As a consequence, the crop depends on frequent water applications
and increases its susceptibility to water stress during extremely hot weather.
High-velocity winds can uproot large trees with shallow root systems.
Chapter 3. THE DISTRIBUTION OF WATER IN THE SOIL
The flow of water and its distribution within the soil by drip irrigation is different from
that obtained with other irrigation techniques. Water is applied from a point or line
source. Point sources are discrete drippers which each of them wets a discrete
volume of soil. Line sources are drip laterals in which the drippers are installed close
to each other. The water flows along the lateral so that the wetted volumes formed by
adjacent emitters, overlap and create a wetted strip. With on-surface drip irrigation,
the wetted soil surface area is a small fraction of the total soil surface area. A small
pond is created beneath each emitter. The pond's dimensions depend on the soil
type and the emitter's flow rate. In light sandy soil, the pond is tiny and is actually
hardly observed. In soils of heavier texture, the pond's diameter is greater. Water
distribution within the soil follows a three-dimensional flow pattern, compared with the
one-dimensional, vertical percolation pattern typical of flood and sprinkler irrigation
that wet the entire soil surface area. With subsurface drip irrigation, the wetting
pattern is quite different. Water moves downward, sideways and also upwards.
Fig. 4. Water distribution in the soil along time: (a) on-surface drip irrigation. (b) SDI
Two driving forces simultaneously affect the flow of water in the soil: gravity and
capillary force. Gravity drives the water downwards. Capillary forces drive the water
in all directions. The equilibrium between these two forces determines the distribution
pattern of water within the soil.
The water distribution pattern affects the spreading of the roots in the soil and also
the distribution and accumulation of the dissolved chemicals - nutrients and salts.
Soil Wetting Patterns
The main factors affecting the distribution pattern of water and solutes in the wetted
soil volume with drip irrigation are listed below:
Capillary forces are more pronounced in finer textured soils than gravity; hence the
horizontal width of the wetted soil volume is greater than the vertical depth. The
wetted volume shape resembles the shape of an onion. In medium textured soils, the
wetted volume is pear-shaped, and in soils with a coarse texture the vertical water
movement is more pronounced than the horizontal one so that the wetting volume
resembles a carrot.
Soil structure also influences water distribution. Compact layers and horizontal
stratification enhance the horizontal flow of water at the expense of vertical
percolation. On the other hand, vertical cracking in compacted soils enhances
preferential downward flow of water followed by incomplete wetting of the upper soil
The greatest wetting horizontal diameter by drippers of on-surface drip laterals
is near the soil surface, 10 – 30 cm deep.
The greatest wetting horizontal diameter by drippers of subsurface drip laterals
is at the depth of the lateral.
The vertical dimension of wetted soil above the emitter in SDI is about ¼ of the
wetted width in sandy soil and about ½ of the wetted width in silty and clayey soils.
Emitter Flow Rate
For the same application
time-length and amount
of water applied:
• A lower flow rate
renders a narrow
• A higher flow rate
renders a wider
ponds and the
diameter is bigger
than in lower flow
For the same application
time-length and volume of water applied:
Narrow spacing with overlapping renders narrower and deeper wetting pattern. The
wetted width by each dripper increases until adjacent circles overlap. After
overlapping, most of the flow is directed downwards
Fig. 5. Water distribution from a single dripper in loamy
and sandy soil. 4 l/h and 16 l/h flow rates, 4, 8, 16 l dose
After Bressler 1977
Wide spacing renders wider and shallower wetting pattern.
The wetted volume grows wider and deeper as the applied water amount increases.
Chemical Composition of the Water
Chemical compounds dissolved in the water may change the wetting pattern.
Detergents and other surfactants contained in reclaimed and storm waters reduce
water's surface tension and decrease the horizontal flow.
The lower surface tension increases the affect of gravity at the expense of the
capillary forces, resulting in a narrower and deeper wetting pattern.
Salt and Nutrient Distribution
Dissolved salts tend to accumulate at the perimeter of the wetted zone, particularly at
the soil surface where the water content of the soil is lower. A saline ring develops
around the wetted circles on the soil's surface, along with a zone of salt accumulation
at a depth which depends on the leaching efficiency. Good drip irrigation
management at an appropriate irrigation frequency, replenishes the water removed
by the crop, so that the soil water content in the soil remains high enough to maintain
a low concentration of soluble salts. The nutrients applied with the irrigation water
also follow the same distribution pattern.
Fig. 6. Salt distribution in the wetted volume
Adapted from Kremmer & Kenig, 1996
Fig. 7. Leaching of salt into the active root-
zone by rain Adapted from Kremmer & Kenig, 1996
Salt accumulation at the soil's surface and in the uppermost soil layer requires
implementation of preventive measures with the first rains after a dry season.
Irrigation should be applied as long as the rain lasts as to avoid the accumulation of
the salts leached from the soil surface into the active root-zone.
Soil Properties that affect the Water Distribution Pattern
As mentioned before, soil properties affect the flow of water in the soil as well as the
pattern of the wetted volume.
The balance between the vertical and the horizontal movement is determined by soil
properties such as infiltration and percolation rates that are dependent on the soil’s
hydraulic conductivity. Hydraulic conductivity is expressed in units of velocity
(length/time) per unit cross section (m/sec). A given soil does not have a constant
value of hydraulic conductivity. In one and the same soil the hydraulic conductivity is
higher in saturated soil than in unsaturated state. It also depends on the degree of
stratification - the presence of compact soil layers and the moisture content of the soil
before irrigation. Though different mathematical models have been developed for the
prediction of soil water distribution patterns, the use of empirical field techniques for
the estimation of the size and volume of the wetted soil is preferable.
While plants are not consuming water, as it happens at night, the volume of the soil
that is wetted depends on the volume of water applied by the dripper and the change
in water content in the wetted volume.
V = L X [100/(Mf-Mi)]
V = Soil wetted volume, l'.
L = Amount of the applied water, l'
Mf is the average percentage of water content per unit volume in the wetted zone
after irrigation and Mi is the average percentage of soil water content per volume unit
For example, if 100 l' of water were applied at night and the soil water content in the
wetted volume increased by 10% per volume, then the wetted volume would be 1000
l' (1 m3
) of soil.
Mf – Mi = 10%
V = 100l X (100/10) = 1000l
Wetting Width and Depth
Selection of the most suitable dripper and determination of the spacing between
laterals and between drippers on the lateral, commit a thorough estimation of the
wetting pattern of the soil by the drippers.
For a simple estimation of the width and depth of soil wetting, it is assumed that the
capillary forces drive the flow of water in the soil at the same rate in all directions and
gravity drives the water downward. For a given amount of applied water, the balance
between these two forces determines the dimensions of the soil wetted volume and
the ratio between the vertical and horizontal axis. During the wetting of a dry soil,
gravity initially drives the water downwards through the empty, non-capillary voids
much faster than the horizontally capillary movement. As the capillary voids are filled
with water, the horizontal flow becomes more pronounced. This happens earlier at
higher flow rates, therefore the horizontal diameter of the wetted volume by drippers
with higher flow rates is larger. The same happens with soils of fine texture. Vertical
gravity-driven percolation is slower and the capillary voids are filled earlier with water.
Schwarzman and Zur developed a semi-empirical formula for estimation of the
dimensions of the wetted volume:
W = K3 (Z)0.35
When: W = Max width of the wetted volume (not of the wetted area on soil surface)
K3 = 0.0094 (empirical coefficient)
Z = Desired depth of the wetting front – m (related to depth of the active root system).
q = Dripper flow rate l/h
Ks = Saturated hydraulic conductivity – m/s (has to be measured in laboratory or
taken from a table)
The result of using this formula differs in many cases from the empirical
measurements in the field, since the hydraulic conductivity is determined in the
laboratory on a disturbed soil sample. Whenever possible, it is recommended to
determine the wetting pattern in undisturbed soil in the field.
The distribution of nutrients applied by fertigation depends significantly on the
interaction between the nutrient ions and the soil.
Potassium ions are absorbed on the surface of clay minerals so that their transport
with irrigation water in fine and medium textured soils is limited and most of the
applied potassium remains in the upper soil layers.
Phosphorous precipitates from the soil solution as insoluble salts with calcium and
magnesium in basic and neutral pH levels and with iron and aluminum in acid soils.
In these cases, it remains in the upper soil layer. In SDI, application of phosphorous
in deeper soil layers increases its availability and absorption by the root system.
Root System Development under Drip Irrigation
It is well known that the water application regime and water distribution pattern in the
soil affect the pattern of root system development.
Each plant family has a typical root distribution pattern, stemming from the growing
conditions in the plant’s site of origin and its adaptation of the plant to the local
Fig. 8. Diverse root systems
As depicted in the above drawing, root systems can be shallow or deep, dense,
branched or sparse, mostly unrelated to the shape of the plant's canopy.
The root system pattern and soil properties are important factors in determining
dripper spacing and the scheduling of the irrigation regime. Shallow and sparse root
systems require a close dripper spacing and frequent water applications, while deep
and branched root systems allow for wider spacing and larger intervals between
Frequent and small water applications
by drip irrigation lead to the
development of shallow and compact
root systems. This increases crop
sensitivity to heat spells and water
stress. Large plants with shallow root
systems are prone to uprooting by
On the other hand, because of the
improved aeration and nutrition in the
drip irrigated soil volume, the density of
the active fine roots is significantly
higher than the density of root systems that grow under sprinkler irrigation.
grow under sprinkler irrigation.
Fig. 10. Root system in drip irrigation (left) vs. root system in sprinkler irrigation (right) Courtesy “Netafim”
The active root system and most root-hairs of drip-irrigated orchard trees, are
concentrated in the wetted volume. The highest density of the active roots is in the
aerated upper layers, provided there is no accumulation of salts. At the margins of
the wetted volume, where salt accumulates, active roots are sparse.
Evergreen fruit trees such as avocado and citrus develop shallower root systems
under drip irrigation than deciduous orchards and vineyards. This determines the
irrigation regime and necessitates the addition of a second drip lateral per row on
light textured soil.
With SDI, the root distribution pattern is different. Roots are mainly concentrated
under and beside the laterals. Very few roots develop above the laterals due to the
higher salinity in these soil layers.
Fig. 9 Typical root systems of field crops
Chapter 4. THE DRIP SYSTEM
Although the drippers are the core of the drip irrigation network, the system is made
up of many additional components. These components have to be compatible with
each other, with the crop demands and with the characteristics of the plot to be
The components are classified in six principal categories:
• Water source: A pumping system from an on-surface or underground source
or a connection to a public, commercial or cooperative supply network
• Delivery system: Mainline, sub-mains and manifolds (feeder pipes)
• Drip laterals
• Control accessories: Valves, water meters (flow-meters), pressure and flow
regulators, automation devices, backflow preventers, vacuum and air release
• Filtration system
• Equipment for the injection of plant nutrients and water treatment agents
The Water Pumping/Supply Head
There are two alternative sources of
a. independent pumping from an on-
surface source (such as a lake, river,
stream, pond or dam reservoir) or from
an underground source (such as a well).
b. connection to a commercial, public or
cooperative supply network on the other.
With independent pumping, the pump is
chosen according to the discharge and
pressure requirements in the irrigated
In connection to a water supply network,
the diameter of the connection, main
valve and the delivering pipeline should
correspond with the planned flow-rate and the requested operating pressure, with the
smallest possible friction head losses.
The Delivery System
Mainlines for water delivery and distribution
Pipes are made of PVC or polyethylene (PE). PVC pipes are installed underground
as usually they have no protection against UV-radiation. PE pipes are installed
underground or above ground, as they contain carbon black, which provides UV
protection. The pipes’ PN (nominal working pressure) has to be higher than the PN of
the drip laterals, particularly if the system has to withstand pressure with closed
valves. The most common PN of delivery and distribution lines is 6 – 8 bar (60 – 80
m pressure head).
Fig. 11. Simplified scheme of drip system
The sub-mains are installed under or above ground. Underground installed pipes can
be made of PVC or PE, while above-ground installed pipes can only be made of PE.
In the case of retrieveable drip systems for the irrigation of annual crops (the system
is layed out at the beginning and retrieved at the end of the growing season). Above-
ground pipes can be made of P.E., aluminum or vinyl “lay-flat” hose. The lay-flat hose
is durable and lays flat when not in use, so mechanic equipment can travel over it.
The lay-flat hose, connectors, and feeder tubes are retrieved after the growing
season to be used for the irrigation of another plot or stored until the following
season. Wide-diameter PE pipes are more rigid, and are not easily rolled up at the
end of the season.
In certain circumstances, when rows are very long or in harsh topographic conditions,
sub-division of the plot by sub-mains is insufficient. In these conditions, additional
division is accomplished by manifolds.
Fig. 12. Typical layout of drip irrigation system
The drip laterals are connected to the sub-mains or the manifolds. The laterals are
made of LDPE (Low Density Polyethylene). There are different types of connectors
between the sub-mains/manifolds and the laterals. The connectors have to withstand
the working pressure as well as pressure spikes and water hammers. The lateral may
be laid on soil surface or underground (SDI). Shallow burying, 5 – 10 cm below soil
surface is common in vegetables grown under plastic mulch.
Two basic types of drip laterals are used: Thick-walled laterals with on-line or in-line
discrete drippers and thin-walled tapes with turbulent flow inherent water
passageway molded into the tape during the extrusion process. The tape shrinks
when it is not under water pressure. Thick-walled laterals have a PN of 1 – 2 bar (10
– 20 m), and tapes have a PN range from 0.4 to 1 bar (4 – 10 m).
Control and Monitoring Accessories
Valves and Gauges
Simultaneous irrigation of several plots, each one with different water requirements
from a single water source requires the sub-division of the irrigated area into sectors,
each controlled by its assigned valve. These valves can be operated manually or
automatically. Water-meters as well as automatic water-metering valves are used to
measure and control water supply to the various sectors.
Pressure regulators are used to prevent excessive pressure above the working
pressure of the system.
A backflow prevention/anti-siphon valve is required if the water is supplied from a
well or a municipal water source that distribute drinking water, when fertilizers or
other chemicals are injected into the irrigation system.
Air-release/relief valves have to be installed at the highest topographic points of the
system in order to avoid interference with water flow, excessive friction with pipe
walls and pipe burst as an outcome of the flow of a high volume of air in the system.
Vacuum breakers are used to avoid the collapse of pipes in steep slopes. In SDI
systems, they are installed to avoid suction of soil particles into the drippers after
shut-down of the water supply.
Fig. 13. Components of drip irrigation system
The narrow passageways of the emitters are susceptible to clogging by suspended
matter and chemical precipitates from the irrigation water. Three measures are taken
to prevent clogging:
• Preliminary separation of suspended solid particles by settling ponds, settling
tanks and sand separators.
• Filtration of the irrigation water.
• Chemical treatments for decomposition of suspended organic matter, blocking
the development of slime by microorganisms and prevention of precipitates
Filtration devices are usually installed at the control head. When the irrigation water
is heavily contaminated, a main filtration system is installed at the plot control head
and secondary control filters are installed at the sectorial control heads. Filters should
be flushed and cleaned routinely. Flushing can be manual or automatic. Automatic
back-flushing of media filters is performed with filtered water, hence, the filters are
installed in pairs and flush one-another alternately.
Three types of chemicals are injected into drip irrigation systems: fertilizers,
pesticides, and anti-clogging agents. Fertilizers are the most commonly injected
substances; the ability to “spoon-feed” nutrients contributes to the increased yields
obtained with drip irrigation.
Systemic pesticides are injected into drip irrigation systems to control insects and
protect plants from certain diseases.
Chemicals that clean drippers or prevent dripper clogging are also injected.
Chlorine is used to kill algae and microorganisms and for decomposition of organic
matter, while acids are used to modify water pH and dissolve precipitates.
The different types of injectors are described in the chapter on fertigation.
Fig. 14. Control Head Courtesy “Netafim”
Chapter 5. FLOW RATE - PRESSURE RELATIONSHIP
Water pressure is a key factor in the performance of pressurized irrigation systems.
Pressure can be expressed in different unit systems.
Table 1. Pressure units
Definition Unit Sub units Conversion
Pressure/Tension Bar =100 Centibar 0.99 Atm.
Pressure/Tension Kilopascal (kPa) = 1000 Pascal 0.01 Bar=1 Centibar
Pressure/Tension Atmosphere (Atm) ~100 Centibar 1.01 Bar
Head Meter =100 cm 0.1 Atm. ~ 0.1 Bar
For simplicity and convenience in the design of irrigation systems, the preferred unit
system is pressure head, expressed in meters (m) height of water column. Pressure
is converted to head units by dividing the pressure (weight/area) by the water’s
specific weight (weight/volume). Therefore the head units are length (m) units.
For example: A pressure of 5 atmospheres (5 kg/cm2
) divided by water’s specific
weight (1 g/cm3
) equals (5000 g/cm2
) = 5000 cm = 50 m. In practice, a
column of water with cross section of 1 cm2
and weighing 1 Kg is 10 m high.
This unit system enables the concurrent calculation of the effects of topography and
friction losses due to the flow of water in the pipes on the pressure head at each
point of the irrigation system. Water pressure head can be referred to as the water’s
hydraulic potential energy. This potential energy is capable to accomplish work, e.g.
to move a certain mass of water along a certain distance.
Water Head Components
The total water head, measured at a specific point of the irrigation system, is made-
up of three components:
Elevation Head (z)
Elevation head is due to the topographical position, the relative height of a given
point above or below a fixed point of reference. For example, if the main valve in the
plot lies 5 m above the distal end of the plot, the measured static (elevation) head at
the distal end will be 5 m higher than the measured static head at the valve. Static
head is the pressure measured in a point in the water system when no water flow is
Water under high pressure has more energy than water under low pressure.
Although water is considered incompressible, water under pressure is stressed by
the pressure. The resultant stress compresses the water and squeezes the bonds
and electric fields in and around the water molecules. The water absorbs the energy
that pushes the water molecules back against the surrounding water molecules and
the container wall. The energy stored in the water molecules and the bonds between
them is available to move the water to lower energy points.
Flowing water has kinetic energy (velocity energy) represented by V2
/2g where V is
velocity which is measured in m/sec and g is the gravitational constant 9.81 m/sec2
Squaring V by itself (V x V = V2
) results in units of m2
which divided by g in m
gives velocity head in m. units.
Conservation of Hydraulic Energy
Globally, energy is never perished, it only changes forms. Hydraulic energy may
change back and forth between the three forms; elevation energy, pressure energy
and velocity energy. Some of it may be lost from the system and dissipated as heat
due to friction, but it is still all there. If the sum of the three energy components does
not remain constant as water flows through the irrigation system, then energy must
either be added by a pump or booster, or be lost by friction. Between any two points,
point 1 and point 2, in a closed system, changes in energy are accounted with the
P1 + V12/2g + Z1 + Energy Added (pump head) = P2 + V22/2g + Z2 + Head Losses
Initial Hydraulic Energy Final Hydraulic Energy
Pressure Head @1 + Velocity Head @1 + Elevation Head @1 + Pump Head Added
Pressure Head @2 + Velocity Head @2 + Elevation Head @ 2 + Friction Losses
The above expression is known as Bernoulli’s Equation which is used to solve
hydraulic problems in irrigation systems.
The two dynamic components in this expression are the pump’s energy (added) and
the friction losses (subtracted).
Head losses are the consequence of friction between the pipe's walls and water as it
flows through the system and meets obstacles (turns, bends, expansions and
contractions) along its way.
The degree of head loss is a function of the following variables:
a. Pipe length
b. Pipe diameter
c. Pipe wall smoothness
d. Water flow-rate (discharge)
e. Water viscosity
Diverse theoretical and empirical equations have been developed to calculate these
There are two types of friction losses: friction losses in water flow along straight
pipes, defined as major losses; and friction losses due to the turbulent flow at bends
and transitions, defined as minor (local) losses. If the flow velocities are high and
there are many bends and transitions in the system, minor losses can build-up and
be quite considerable. The most common equation used to compute friction losses
of water flow along a pipe is known as the Hazen-Williams formula.
J = 1.135 x 1012
J = head loss (‰ =m/1000 m)
D = inner pipe diameter (mm)
C = friction coefficient (indicates pipe wall smoothness, the higher the C
coefficient, the lower the friction head loss)
Q = flow-rate (m3
Minor (local) Head Losses
Minor head losses are usually
defined as equivalent length
factors which add a virtual
length of straight pipe in the
accessory same diameter to
the length of the pipe under
Total Dynamic Head
The total dynamic head
created by the pump is the
sum of the pumping suction lift (the difference between water surface height at the
source and pump height), the requested working pressure in the emitters, and friction
losses within the irrigation system.
The energy consumed per pumped unit of irrigation water depends on the total
dynamic head provided by the pump and the pumping system's efficiency. The total
dynamic head depends on:
• Vertical distance that the water is lifted
• Pressure required in drippers' inlets
• Friction losses in the pipeline along the way from the water source through filters,
valves, pipelines and manifolds on the way to the emitters
Pumping system efficiency depends upon the pump efficiency, its power unit
efficiency, and the efficiency of power transmission of power between them.
The power output required by the pump is calculated with the formula below:
Q x H
N = ----------
270 x ŋ
Where: N = required input – HP
Q = pump discharge – m3
H = total dynamic head – m
η = pump efficiency – decimal fraction
Example: Q = 200m3
H = 150 m;
ηηηη = 0.75.
N = 200 X 150/(270 X 0.75) = 148 HP
When measuring pressure, it should be remembered that the pressure gauges are
calibrated to read 0 (zero) at atmospheric pressure (about 1 bar). It is important to
Table 2. The friction coefficient ( C ) of pipes
PVC and PE 140-150
New steel 110-120
5 year old steel 80-90
Steel with internal concrete coating 110-120
remember this fact for the operation of devices such as Venturi suction injectors in
Absolute pressure is the formal expression of total force per unit area. It is composed
of the pressure of the atmosphere, the pressure due to any external forces applied
on the fluid and the pressure resulting from the weight of the fluid itself.
The gauge pressure is the absolute pressure minus the atmospheric pressure that
typically acts in all directions and on all objects in open air. Since atmospheric
pressure at sea level height is typically about 1 bar, an absolute pressure of 3 bars
would be equivalent to a gauge pressure of 2 bar (~20 m pressure head).
The working pressure is the pressure required at the emitters to guarantee effective
performance and uniform water distribution. The range of the appropriate working
pressure of the emitter is defined and published by the manufacturer in the operating
guide. The type of the emitter chosen and its working pressure, have to be taken into
account in the design of the irrigation system and in the irrigation scheduling. The
distributing pipelines are designed to deliver the water to the emitters with such
pressure losses that guarantee the appropriate working pressure in the emitters, so
that water will be applied uniformly in the whole irrigated block.
Although there are a number of formulae for calculation of head losses, in daily life,
tables, nomograms and dedicated software are mostly used.
When calculating the head losses in a pipe network, a distinction is made between
the flow in pipes with a single outlet at their distal end and distributing pipes with
multiple outlets. In a non-distributing pipe, head loss values taken from a table or a
nomogram are expressed in % or ‰ units by its length in m. Multiplication by the pipe
length in m. length units renders the actual losses in m. head units.
Christiansen friction factor (F) is used also to calculate the head losses in pipes with
multiple outlets such as drip laterals, This factor accounts for the decrease in flow
along the lateral and depends upon the number of outlets or emitters (N) and the
exponent (m = 1.852) of (Q) in Hazen-Williams equation. The formula to calculate
this factor is as follows
F = 1/(m+1) + 1/(2N) +((m-1)0.5
For a lateral with more than 10 emitters, F= 0.35 can be used regardless of which
friction loss calculation formula is used. The head loss due to friction in drip laterals is
then determined by Hl = F(Hlp), where Hl is the head loss due to friction in the drip
lateral and Hlp is the head loss due to friction of the same discharge in a pipe of the
same diameter and length but with a single outlet at the end. As mentioned above, Hl
= 0.35 Hlp can be used when there are more than 10 outlets on the pipe.
Hydraulic Characteristics of the Emitter
The flow-rate of emitters in micro-irrigation is affected variably by pressure
fluctuations. The performance of a given model depends on its design and
construction. The relationship between the emitter operating pressure and flow-rate
is calculated with the following equation:
Q = kPe
Where: Q = dripper flow-rate – l/h
k = dripper constant – depends on the units of flow rate and pressure head.
P = Pressure at the dripper's inlet – m
e = dripper discharge exponent (dripper exponent)
The dripper exponent indicates the specific relationships between the working
pressure and the flow-rate of the emitter. The range of emitter exponents is 0 – 1.0
Drippers with laminar flow pattern have high exponents, in the range of 0.7 – 1.0.
Drippers with turbulent flow pattern have exponents between 0.4 and 0.6.
Compensating drippers have exponents which approach zero in the regulated flow
The larger the dripper exponent, the more sensitive the flow-rate is to pressure
variations. A value of 1 means that for each percent change in pressure there is an
identical percent change in flow rate. On the other side, an exponent value of 0 (zero)
means that the emitter flow-rate does not change at all as pressure changes.
Table 3. The effect of dripper exponent on pressure – flow-rate relationships
% flow rate change% pressure
Exponent ----> 0.4 0.5 0.6 0.7 0.8
10 3.9 4.8 5.9 6.9 7.9
20 7.6 9.5 11.6 13.6 15.7
30 11.1 14.0 17.1 20.2 23.3
40 14.4 18.3 22.3 26.6 30.9
50 17.6 22.5 27.5 32.8 38.3
Fig. 15. Relationship between the dripper exponent and lateral length Courtesy “Netafim”
Whenever the laterals are laid out on the soil surface, the ambient temperature
affects dripper flow-rate. As water temperature increases, water viscosity decreases
and the discharge increases. Lateral heating is more pronounced at the distal end
due to decrease in flow velocity. As a result, the emitters in the lateral's end may
have a higher flow-rate than the emitters at the beginning of the laterals.
In pressure compensating
(PC) drippers, pressure
fluctuations above the
threshold of the regulating
pressure do not affect the
flow-rate. The regulating
pressure is that head
range in which regulation
of flow-rate takes place.
The graphs to the right
show that in Ram PC
drippers, the regulating
pressure threshold is
about 4 m.
Calculation of the Head
As mentioned before, slide
rulers, tables, nomograms,
hand-held and on-line
calculators as well as
dedicated software can be
used for the calculation of
head losses. Pipe and
accessories manufacturers publish tables and nomograms depicting the head losses
in their products. Valve producers use the Kv coefficient that designates the
discharge of the valve in m3
/h at which 10 m head (1 bar) are lost by friction.
Table 4. Head losses in Acuanet automatic valve
1" El/St 1½" El/An 1½" El/St 1½" Hy/St 2" El/St 2" Hy/An 2" Hy/St 2" Hy/An
3 1.6 0.5 0.4 0.3 0.3 0.2 0.3 0.2
5 2.3 0.5 0.4 0.3 0.6 0.4 0.3 0.3
7 4.7 1.3 1.0 0.7 0.9 0.7 0.5 0.8
10 2.2 1.8 1.3 1.5 1.0 1.0 1.0
12 3.0 2.2 1.3 1.9 1.3 1.4 1.2
14 3.5 2.8 2.2 2.4 1.7 3.4 1.4
16 4.6 3.4 3.0 3.0 1.9 2.4 1.6
18 5.8 4.3 4.0 3.6 2.4 3.2 2.1
20 6.6 5.2 4.7 4.2 2.9 3.8 2.6
24 8.5 6.5 6.5 5.6 3.8 5.5 3.6
28 7.2 4.9 7.2 4.6
32 9.6 8.8 8.5 6.4
El=Electric; An=Angular; St=Straight;Hy=Hydraulic Courtesy "Netafim"
Fig. 16. Pressure Compensated dripper flow-pressure relationship
Fig. 17. Non-pressure compensated flow-pressure relationship
Dripper manufacturers provide detailed technical
data, in catalogues or on-line, about the flow-rate -
pressure relations of their products, such as the
dripper's coefficient and the dripper exponent. This
information should be utilized for the design of
lateral length and the pressure required at the
lateral's inlet. Low dripper exponents allow higher
pressure difference between drippers without
deviating from the rule allowing flow-rate difference
of 10%. (This rule is dealt with in the topic on
Adapted from "Plastro" CD-Rom
This example shows that a large difference in pressure head – up to 20%, is
tolerated for drippers with a dripper exponent of 0.5 and below.
A comprehensive nomogram for the estimation of friction losses in straight pipe
sections that can be used with any type of pipe is presented overleaf. The example
shows the head loss (in J ‰) for a flow-rate of 200 m3
/h through a pipe with an inner
diameter of 200 mm.
The first step is to draw a straight line from Q=200 on the left scale through the 200
mm point on the D mm scale. The crossing point of the ruler with the axis (the blank
line) has to be clearly marked.
The second step is to draw a straight line connecting the mark through the relevant
friction coefficient on the scale C and to mark the point where this line crosses the
/00. The value of the crossing point is the head loss in 0
/00 (m pressure head
per 1000 m length of the pipe.
The following nomograms are useful for LDPE and HDPE pipes. In each nomogram,
the relevant PN values are designated under "Class".
Fig. 18. Acuanet automatic valve
Table 5. "Plastro" Hydrodrip II integral drip laterals technical data
DRIPPER CONSTANTS DH=7.5% DH=10%EMITTER
INTERNAL COEFFICIENT EXPONENT Pmin-m Pmax-m Pmin-m Pmax-m
12-/26/40 2.1 12 10.4 0.6442 0.506 9.25 10.75 9 11
16/18 1.6 16 15.2 0.5300 0.4830 9.19 10.81 8.91 11.09
2.2 16 15.2 0.7260 0.4840 9.19 10.81 8.91 11.09
3.6 16 15.2 1.1940 0.4792 9.19 10.81 8.90 11.10
16-/25/35 1.7 16 15.2 0.5212 0.5090 9.24 10.76 8.97 11.03
-40/45 2.3 16 15.2 0.7646 0.4704 9.17 10.83 8.88 11.12
3.6 16 15.2 1.1940 0.4792 9.19 10.81 8.90 11.10
20-/24/36/44 1.7 20 17.6 0.5212 0.5090 9.24 10.76 8.97 11.03
2.3 20 17.6 0.7646 0.4704 9.17 10.83 8.88 11.12
3.6 20 17.6 1.1940 0.4792 9.19 10.81 8.90 11.10
25-/17/34 1.7 25 22.2 0.5212 0.5090 9.24 10.76 8.97 11.03
2.3 25 22.2 0.7646 0.4704 9.17 10.83 8.88 11.12
3.6 25 22.2 1.1940 0.4792 9.19 10.81 8.90 11.10
Fig. 19. Head loss nomogram, based on Hazen-Williams formula
Fig. 20 Nomogram for calculation of head losses in HDPE pipes Adapted from "Plassim" brochure
Fig. 21 Nomogram for calculation of head losses in LDPE pipes Adapted from "Plassim" brochure
The class designation relates to the working pressure (PN) in atm. 1atm = 10 m ≈ 1 bar
Chapter 6. PIPES AND TUBES FOR DRIP IRRIGATION
The commercial development of drip irrigation is based on the use of plastic
materials. Drippers, pipes and most of the other drip system components are made of
Plastic solid materials are comprised of one or more polymeric substances that can
be shaped by molding or extrusion. Polymers, the basic ingredient of plastic
materials, are a broad class of materials that include natural and synthetic
substances. In professional terminology, polymers are frequently defined as resins.
For example, a polyethylene (PE) pipe compound consists of PE resin combined with
colorants, stabilizers, anti-oxidants and other ingredients required to protect and
enhance the quality of the material during the fabrication process and operation in the
Plastic materials are divided into two basic groups: thermoplastics and thermosets,
both of which are used for the production of plastic pipes.
Thermoplastics include PE, polypropylene, polybutylene and PVC. These materials
can be re-melted by heat. The solid state of thermoplastic materials is the result of
physical forces that immobilize polymer chains and inhibit them from slipping past
each other. When heat is applied, these forces weaken and allow the material to
soften or melt. Upon cooling, the molecular chains stop slipping and are held firmly
against each other in the solid state. Thermoplastics can be shaped during the
molten phase of the resin and therefore can be extruded or molded into a variety of
shapes, such as pipes, flanges, valves, drippers and other accessories.
Thermoset plastic materials are similar to thermoplastics prior to a chemical reaction
(“curing”) by which the polymer chains are chemically bonded to each other by new
cross-links. That is usually performed during or right after shaping of the final product.
Cross-linking is the random bonding of molecules to each other to form a giant three-
dimensional association. Thermoset resins form a permanent insoluble and infusible
shape after applying heat or a curing agent. They cannot be re-melted after shaping
and curing. This is the main difference between thermosets and thermoplastics. As
heat is applied to a thermoset component, degradation occurs at a temperature lower
than the melting point. Thermosetting resins can be combined with reinforcements to
form strong composites. Fiberglass is the most popular reinforcement and fiberglass-
reinforced pipe (FRP) is a common form of thermoset-type pipes.
Polyethylene (PE) is the most prevalent material in pipes and laterals in drip irrigation
systems. There are four types of PE, classified by material density:
Type I – Low Density (LDPE), 910 – 925 g/l
Type II – Medium Density (MDPE), 920 – 940 g/l
Type III – High Density (HDPE), 941 – 959 g/l
Type IIII – High Homo-polymer, 960 and above g/l
Carbon black 2% is added to reduce pipes’ sensitivity to ultraviolet (UV) sun
PE pipes can be classified according to the working pressure (PN) they can
withstand. The common grades of PN used in irrigation are: 2.5, 4, 6, 10, 12.5 and 16
bars (atm). Some thin-wall laterals withstand much lower PN: 0.5 – 2 bar. The
tolerance to working pressure depends on pipe density and wall thickness. The
tolerance data given by the producers relates to temperature of 20 C0
. In higher
temperatures, the tolerance decreases significantly, hence pipes are tested at twice
their designated working pressure.
Plastic pipes are defined according to their external diameter, in mm. In the USA and
some other countries, pipe diameter is defined by imperial inch units (“). 1” = 25.4
mm. Pipe wall thickness is also defined in mm units (in the USA by mil units - 1/1000
of inch). 1 mil = 0.0254 mm.
Laterals are commonly made of LDPE (PE grade 32) while delivering and distributing
pipes with diameters greater than 32 mm are mostly made of HDPE.
HDPE pipes are further classified according the grade of the material: PE-63, PE-80,
PE-100. The higher the grade, the higher the pipe quality.
Table 6. PE (polyethylene) pipes for agriculture
PE type ND Applications PN - m
LDPE 6 mm Hydraulic command tubing 40 – 120
LDPE 6 – 10 mm Micro-emitters connection to laterals 40 – 60
LDPE 12 – 25 mm Thin-wall drip laterals 5 – 20
LDPE 12 – 25 mm Thick-wall drip laterals 25 – 40
LDPE 16 – 32 mm Micro and mini emitter laterals 40 – 60
HDPE 32 – 75 mm Sprinkler laterals 40 – 60
HDPE 40 – 140 mm Main lines and sub-mains 40 – 100
HDPE 75 – 450 mm Water supply networks 60 - 160
Table 7. Internal diameter and wall thickness of LDPE pipes
OD/PN 25 m 40 m 60 m 80 m 100 m
mm ID Wall
12 9.8 1.1 9.6 1.2 9.2 1.4 8.6 1.7 8.0 2.0
16 13.2 1.4 12.8 1.6 12.4 1.8 11.6 2.2 10.6 2.7
20 17.0 1.5 16.6 1.7 15.4 2.3 14.4 2.8 13.2 3.4
25 21.8 1.6 21.2 1.9 19.4 2.8 18.0 3.5 16.6 4.2
32 28.8 1.6 27.2 2.4 24.8 3.6 23.2 4.4 21.2 5.4
40 36.2 1.9 34.0 3.0 31.0 4.5 29.0 5.5 26.6 6.7
50 45.2 2.4 42.6 3.7 38.8 5.6 36.2 6.9 33.4 8.3
Adapted form "Plastro" brochure
ND = Nominal Diameter
OD = External (Outer) Diameter. In plastic pipes it is mostly equivalent to the ND.
ID = internal (inner) Diameter
Table 8. Internal diameter and wall thickness of HDPE pipes
OD/PN 25 m 40 m 60 m 80 m 100 m 160 m
mm ID Wall
12 8.6 1.7
16 12.8 1.6 11.6 2.2
20 16.8 1.6 16.2 1.9 15.4 2.8
25 21.8 1.6 21.1 1.9 20.4 2.3 18.0 3.5
32 28.8 1.6 28.2 1.9 27.2 2.4 26.2 2.9 23.2 4.4
40 36.8 1.6 35.2 2.4 34.0 3.0 32.6 3.7 29.0 5.5
50 46.8 1.6 46.0 2.0 44.0 3.0 42.6 3.7 40.8 4.6 36.2 6.9
63 59.8 1.6 58.2 2.4 55.4 3.7 53.6 4.7 51.4 5.8 45.8 8.6
75 71.2 1.9 69.2 2.9 66.0 4.7 64.0 5.5 61.4 6.8 54.4 10.3
90 85.6 2.2 83.0 3.5 79.2 5.5 76.8 6.6 73.6 8.2 65.4 12.3
110 104.6 2.7 101.6 4.2 96.8 6.6 93.8 8.1 90.0 10.0 79.8 15.1
125 118.8 3.1 115.4 4.8 110.2 8.1 106.6 9.2 102.2 11.4 90.8 17.1
140 133.0 3.5 129.2 5.4 123.4 9.2 119.4 10.3 114.6 12.7 101.6 19.2
160 152.0 4.0 147.6 6.2 141.0 10.3 136.4 11.8 130.8 14.6
180 172.2 4.4 166.2 6.9 158.6 11.8 153.4 13.3 147.2 16.4
Adapted form "Plastro" brochure
PVC (Polyvinyl Chloride) is a rigid polymer. To soften the material and enable its
shaping, it is common to add substantial amounts (up to 50%) of plasticizers. These
additives render flexibility to tubes made of soft PVC. PVC pipes are sensitive to UV
sun radiation. Soft flexible PVC pipes are used in a limited scale mainly in gardening
and landscape. Their life span is short. Rigid PVC pipes are used In agriculture
mainly for water delivery and distribution. PVC pipes are installed underground only,
to avoid UV radiation damage. In the last decade, UPVC (unplasticized PVC) pipes
are preferred because of their improved durability and ability to withstand pressure.
PVC pipes appear in discrete 4 – 8 m long segments and have to be jointed in the
field. The working pressure of rigid PVC pipes is 6 – 24 bars (60 – 240 m).
Table 9. PVC pipes for agriculture
PVC type ND Applications PN - m
Soft PVC 6 mm Hydraulic command tubing 40 – 80
Soft PVC 6 – 10 mm Micro-emitters connection to laterals 40 – 60
Soft PVC 12 – 25 mm Thin-wall drip laterals 5 – 20
Rigid UPVC ½” – 4” Risers 40 – 100
Rigid UPVC 63 – 1000
Supply networks, main lines, sub-
40 – 240
When PVC pipes are installed in heavy or stony soil, it is recommended to pad the
trench with sand to avoid damage to the pipe wall caused by soil swelling and stone
Table 10. Internal diameter and wall thickness of PVC pipes
PN------> 60 m 80 m 100 m
OD - mm ID - mm Wall thickness -
ID - mm Wall thickness -
ID - mm Wall thickness -
63 59.0 2.0 58.2 2.4 57.0 3.0
75 70.4 2.3 69.2 2.9 67.8 3.6
90 84.4 2.8 83.0 3.5 81.4 4.3
110 103.2 3.4 101.6 4.2 99.4 5.3
140 131.4 4.3 129.2 5.4 126.6 6.7
160 150.2 4.9 147.6 6.2 144.6 7.7
225 210.2 6.9 207.8 8.6 203.4 10.8
280 262.8 8.6 258.6 10.7 253.2 13.4
315 295.6 9.7 290.8 12.1 285.0 15.0
355 333.2 10.9 327.8 13.6 321.2 16.9
400 375.4 12.3 369.4 15.3 361.8 19.1
450 422.4 13.8 415.6 17.2 407.0 21.5
500 469.4 15.3 461.8 19.1 452.2 23.9
Flexible PVC lay-flat hoses can be used as mainlines and sub-mains. The hose is
impregnated with anti-UV radiation protecting agents. When the water is shut-off, the
hose lays flat on the ground and can be crossed-over by tractors and other farm
machinery. The lay-flat hoses can be laid out on the soil surface or in a shallow
trench. These hoses are available in diameters of 75 – 200 mm.
In addition to UPVC and HDPE pipes, reinforced fiberglass pipes are used to deliver
water under high pressure from the water source to the irrigated area, as a
substitution for steel and asbestos-cement pipes.
GRP (Glass Reinforced Polyester) fiberglass pipes are manufactured in diameters of
300 – 3600 mm and PN grades of 40 – 250 m. They are particularly useful in delivery
of reclaimed water.
External and Internal Pipe Diameter
The internal diameter (ID) of a pipe can be calculated by deducting twice the wall
thickness from the external diameter (OD). In most cases, the nominal pipe diameter
(ND) is the same as its external diameter. Friction head losses of water flow in the
pipe are determined by the internal diameter.
When using nomograms, on-line calculators and design software it is important to
check whether the designated diameter is nominal (mostly external) or internal.
Chapter 7. DRIPPER TYPES, STRUCTURE, FUNCTION AND PROPERTIES
The dripper is the core of the drip irrigation system. Drippers are small water emitters,
made of plastic materials. The design and production of high quality drippers is a
delicate and complicated process. Manufacturing the most effective dripper commits
compromising, taking into account diverse and contradicting demands.
The most important attribute of a dripper is low flow-rate, in the range of 0.1 - 8 liter
per hour (l/h). This low flow-rate can be obtained by different methods. Flow-rate is
determined by the pattern and the dimensions of the water passageway, as well as
the water pressure at the dripper inlet. The smaller the passageway cross-section,
the lower the dripper flow-rate at a given pressure. However, the narrower the
passageway the greater the risk of clogging by suspended solid particles and
Since the water pressure at the dripper's outlet is a key factor in determining flow
rate, reducing that pressure may facilitate a low flow rate through a relatively wide
water outlet. Pressure reduction is achieved by diverse means.
Water passageway pattern: Historically, the initial method for pressure reduction
was a long flow passageway along a tiny micro-tube. Water friction against the wall
of the micro-tube resulted in substantial head losses. The factors affecting the degree
of head loss are: micro-tube length and diameter, micro-tube wall smoothness, flow
pattern and velocity. Initially, the micro-tubes were attached to a lateral and delivered
water at the desired application point. Later, the micro-tubes were wrapped around
the lateral and finally, drippers with internal built-in spiral water passageways were
constructed. The laminar passageway was problematic. The long water path and low
flow velocity led to the precipitation of chemicals that changed the dripper's flow-rate
or plugged it completely.
The labyrinth passageway is a
more advanced design. The water
flows along a labyrinth wherein
the flow direction changes
intermittently and gets a turbulent
pattern with high head losses
along a significantly shorter path
as compared to the spiral dripper,
resulting in the manufacture of
smaller and cheaper drippers. An
additional advantage of this
design is the lower accumulation
of dirt - particles and chemical
precipitations. Later designs
modified the labyrinth
passageway into a zigzag toothed
path with more efficient pressure
dissipation and self-cleaning
attributes. An advanced refinement of the toothed passageway is the turbonet (by
"Netafim") that enables shortening and widening of the water path even further.
Fig. 22. Evolution of the passageway style Courtesy “Netafim”
Turbulent flow has a cleaning effect in the
corners of the water passageways.
The vortex design is another method for
significantly dissipating pressure along a short
passageway. The water enters tangentially into
the dripper and flows in a spiral whirlpool pattern
with high head losses along a short path and
improved prevention of precipitates.
Another type of dripper
is the orifice dripper.
occurs at the tiny water
inlet into the dripper.
The shortening of the
enables fabrication of
small and cheap button
Along with the development of the discrete dripper
technology, a different concept - the trickling tape was
developed. The first product was a perforated plastic tube.
In order to obtain low discharge, the water outlets were tiny
and highly sensitive to clogging. This flaw was eliminated
later by the molding of long labyrinth water passageways
into the tube.
Fig. 27 Tape dripper lateral: empty (left) and filled with water (right) Adapted from "T-Tape" brochure
Dripper systems are classified according to various parameters:
On-Surface Drip Irrigation
This is the prevalent drip technology. It enables convenient monitoring of dripper's
clogging and other disturbances during operation. On the other hand, this method is
susceptible to mechanical damage and degradation by solar radiation; it may
interfere with some farming activities and commits laying out and retrieving the
laterals when irrigating annual crops. In vineyards and some other deciduous
orchards (of apples and pears) grown at the palmeta pruning shape, laterals are
attached to trellises, improving the monitoring of drippers function and decreasing the
hazard of mechanical damage.
Fig. 23. Turbulent flow from "DIS" brochure
Fig. 25. Vortex dripper Adapted from
Karmeli & Keller, 1975
Fig. 24. Orifice dripper
Adapted from Karmeli & Keller, 1975
Fig. 26. Labyrinth
button dripper (“Netafim”)
Subsurface Drip Irrigation (SDI)
This technology has gathered momentum during the last two decades. Although the
system imposes extra costs for burying the laterals into the soil, this technology
simplifies irrigation operation and minimizes interference with other farm activities.
SDI has better water savings and nutrient utilization attributes than on-surface drip
irrigation. It also decreases infestation by weeds. Dripper clogging by root intrusion
and suction of soil particles may hinder proper function and must be avoided by the
proper selection of equipment, competent installation and strict routine maintenance
Layout of Water Outlets along the Lateral
There are two typical arrangements of drippers on laterals that affect the pattern of
water distribution in the soil.
Drippers are installed along the lateral with a spacing that creates a discrete wetted
soil volume by each emitter, without overlapping by the adjacent drippers. This layout
is mostly prevalent with thick wall laterals irrigating orchards and in annuals grown in
Fig. 28. Point-source (left) and line-source (right) wetting by drippers
In a different layout, the drippers are installed along the lateral closed to each other
so that the wetted soil volumes of adjacent drippers along the lateral overlap. This
arrangement is typical with tapes and is the preferred alternative for densely grown
Thick-walled laterals are made of Low Density Polyethylene Pipes (LDPE) with 12 –
25 mm external diameter and 1 – 2 mm wall thickness. The discrete drippers are
installed on-line or inline, 10 – 100 cm apart. The working pressure (PN) is 1 – 4 bar
(10 – 40 m).
Thin-walled laterals are also made of LDPE, however, the wall thickness is only 0.1 –
0.5 mm and the PN is 0.1 – 1 bar (1 – 10 m). Laterals may have discrete drippers
that are molded or inserted in the lateral. A different design is contiguous pressure
dissipation passageways as integral components of a tape.
Structure and Water Passageway Characteristics
As mentioned in the introductory section, the main objectives of the different dripper's
designs is the dissipation of pressure that renders low flow-rates, with minimal
clogging hazard and a cheap emitter. These objectives are achieved by different
methods, as is indicated below.
The water flows through a long and narrow micro-tube. The micro-tube may be a
long one (spaghetti) or a built-in spiral in the dripper's body. Water flow is laminar and
the friction with the tube walls and the internal friction between water molecules
results in pressure dissipation. The discharge (flow-rate) of laminar-flow drippers is
highly sensitive to changes in pressure.
Fig. 29 In-line barbed laminar dripper (left, "Netafim") and turbulent in-line integral dripper (right,
The water flows through a labyrinth that abruptly changes its direction, causing
turbulence. The frequent change of direction within the labyrinth results in high-
energy losses reducing the flow-rate along a relatively wide flow path. This pattern is
more effective in pressure dissipation than the laminar passageway. It enables using
wider water passages and reduces chemical and particle precipitations. The flow-rate
is less affected by changes in pressure in comparison to laminar flow.
Zigzag (Toothed) Path
The shape of the passageway is similar to the labyrinth path. However, the zigzag
flow dissipates more pressure in a shorter path and decreases clogging hazard.
The water enters tangentially into vortex drippers. The water stream hits the walls of
the circular chamber, spins and looses energy. This allows for a relatively short flow-
path and wide-outlet orifice.
The emitter flow rate is determined by the diameter of the orifice. This requires a tiny
aperture that increases clogging hazard.
Location on Lateral
Drippers can be installed externally on the lateral or inserted in-line.
Fig. 30. On-line drippers Courtesy “Netafim”
On-line drippers are inserted into the lateral through punched holes. Drippers can be
added along time according to changes in crop growth and water requirements. The
dripper protrudes from the lateral, making it
sensitive to damage in delivery, installation
and retrieval (when applicable). The
dripper has a barbed or threaded joint that
is inserted or screwed into thick-wall
In-line drippers keep the outer face of the
lateral smooth. There are two versions:
In-line built-in drippers are fused into the lateral during the extrusion process.
Barbed In-line drippers are installed by cutting the lateral and inserting the barbs
into the cut ends of the lateral.
The flow-rate of these drippers can be
adjusted according to the changing
requirements along the growing season.
These drippers have a twist opening locker
that eases the cleaning of fully or partially
clogged drippers during irrigation.
Pressure Compensated (PC) Drippers
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.
Fig. 31. Button drippers conector design
Fig. 32. Adjustable
dripper (above) and flag
Fig. 34. Button and inline PC drippers
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
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.
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 dripper From "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 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.
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
discharge from the emitters, more
air remains in the wetted volume,
compared with drippers of
Extremely low flow-rate drippers are
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 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-
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.
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
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
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
There are two types of pressure regulators. Simple
mechanical devices regulate the pressure against a spring,
Fig. 48. Hydraulic valve
Fig. 49. Spring pressure
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
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