Micro-irrigation Technology and Applications handbook- 2009

MICRO IRRIGATION
TECHNOLOGY AND APPLICATION
Moshe Sne
Irrigation and Plant Nutrition Consultant
SECOND VERSION
NOVEMBER 2009

I
FOREWORD
Since my retirement from the Irrigation and Soil Field Service, on October 2001, after
24 years of service as field adviser and 12 years as its manager, I had been asked to
share my experience and know-how with local and foreign farmers. That had been
implemented in courses, surveys and counseling abroad, as well as in written
publications printed by CINADCO and ICID, and in personal exchange by mail and e-
mail. Irrigation technology is so dynamic that updated publication becomes partially
obsolete in two or three years. The opportunity of uploading professional material to
the web by means of the Scribd system enables me to distribute in real time recently
updated material.
The author
September 24 2009
AUTHOR'S NOTE
Since the upload of the first version of this document, on September 24th
, I received
some dozens of e-mails from readers with comments and suggestions for
improvements in the document. I found some of the comments and suggestions
worthwhile to be embedded in the document. Additionally, I made adjustments on my
own initiative and replaced some outdated figures in this second version.
I would like to thank all the responders for their valuable contribution.
November 28 2009

II
Chap. CONTENT Page
FOREWORD I
CONTENT II
LIST OF TABLES V
LIST OF FIGURES VI
1 INTRODUCTION 1
2 MICRO IRRIGATION 2
2.1 Introduction ………………………………………………………………………………... 2
2.2 Micro-emitter Classification ……………………………………………………………… 2
2.3 Terminology ……………………………………………………………………………….. 3
2.4 Water Distribution Uniformity ……………………………………………………………. 4
3 DRIPPERS: STRUCTURE AND FUNCTION 7
3.1 Introduction ………………………………………………………………………………... 7
3.2 Types of Drip Systems …………………………………………………………………… 7
3.3 Lateral type ………………………………………………………………………………... 8
3.4 Water Passageway Structure and Characteristics ……………………………………. 8
3.5 Position on Lateral ………………………………………………………........................ 10
3.6 Dedicated Drippers ………………………………………………………………………. 11
3.7 Integral Filtration in Drippers ……………………………………………………………. 14
3.8 Auto Flushing Mechanisms ……………………………………………………………… 14
4 MICRO-JETS AND MICRO-SPRINKLERS 15
4.1 Introduction ……………………………………………………………………………….. 15
4.2 Static Micro-jets …………………………………………………………......................... 16
4.3 Vibrating Micro-jets ………………………………………………………………………. 16
4.4 Micro-sprinklers …………………………………………………………………………… 16
4.5 Bubblers …………………………………………………………………......................... 17
4.6 Water Distribution Patterns ……………………………………………………………… 18
4.7 Pressure Compensation …………………………………………………………………. 19
4.8 Emitter Mounting …………………………………………………………………………. 20
5 THE MICRO-IRRIGATION SYSTEM COMPONENTS 21
5.1 The Water Source ………………………………………………………………………... 21
5.2 The Delivery System ……………………………………………………………………... 21
5.3 Laterals ………………………………………………………………………………….. 22
5.4 Control and Monitoring Devices ………………………………………………………… 22
5.5 Sub Surface Drip Irrigation (SDI) ……………………………………………………….. 24
5.6 Low-Cost Drip Irrigation Systems ………………………………………....................... 25
6 PIPES AND ACCESSORIES 28
6.1 Polyethylene Pipes …..…………………………………………………………………… 28
6.2 PVC Pipes ………………………………………………………………………………… 29
6.3 Lay flat hoses …………………………………………………………………………… 30
6.4 Fiberglass Pipes ………………………………………………………………………….. 30
6.5 External and Internal Pipe Diameters ………………………………………………….. 31
6.6 Accessories ……………………………………………………………………………….. 31
7 WATER TREATMENT AND FILTRATION 37
7.1 Physical Quality Parameters ……………………………………………………………. 37
7.2 Chemical Quality Parameters …………………………………………………………… 37
7.3 Emitter Clogging Factors ………………………………………………………………… 37
7.4 Water Hardness …………………………………………………………………………... 38
7.5 Iron and Manganese in Water ………………………………………………………….. 38

III
7.6 Biochemical Oxygen Demand (BOD) ………………………………………………….. 39
7.7 Filtration …………………………………………………………………………………… 39
7.8 Supplementary Water Treatments ……………………………………………………… 47
8 FERTIGATION 49
8.1 Fertilizer Tank …………………………………………………………………………….. 49
8.2 Venturi Injector ……………………………………………………………………………. 49
8.3 Injection Pumps …………………………………………………………………………... 50
8.4 Injection Site ………………………………………………………………………………. 51
8.5 Control and Automation ………………………………………………………………….. 51
8.6 Avoiding Corrosion Damage ……………………………………………....................... 52
8.7 Back-Flow Prevention ……………………………………………………………………. 52
9 MONITORING AND CONTROL 53
9.1 Monitoring …………………………………………………………………………………. 53
9.2 Irrigation Control ………………………………………………………………………….. 55
10 FLOW RATE – PRESSURE RELATIONSHIP 57
10.1 Water Pressure …………………………………………………………………………… 57
10.2 Head Losses ……………………………………………………………………………… 58
10.3 Operating Pressure ……………………………………………………………………… 61
10.4 Hydraulic Characteristics of Emitters …………………………………………………... 62
10.5 Calculation of the Head Losses ………………………………………………………… 64
10.6 Technical Data ……………………………………………………………………………. 64
11 WATER DISTRIBUTION 67
11.1 Soil Wetting Patterns ……………………………………………………………………. 67
11.2 Salt Distribution …………….…………………………………………………………….. 69
11.3 Soil Properties that Affect Water Distribution Pattern ………………………………… 69
11.4 Wetting Width and Depth ………………………………………………………………... 70
11.5 Nutrient Distribution ………………………………………………………………………. 70
11.6 Root System Development Under Drip Irrigation ………………………..................... 71
12 PLANNING OF MICRO IRRIGATION SYSTEMS 72
12.1 Introduction ………………………………………………………………………………... 72
12.2 Planning …………………………………………………………………………………… 72
12.3 Data Manipulation……………………..…………………………………........................ 74
12.4 Existing Equipment ………………………………………………………………………. 78
12.5 Planning of Drip Irrigation for Different Crops …………………………...................... 79
13 DESIGN OF MICRO IRRIGATION SYSTEMS 85
13.1 Basic Guidelines …………………………………………………………....................... 85
13.2 The Design Procedure …………………………………………………………………… 85
13.3 Design of Drip Irrigation System for Row Crops ………………………………………. 88
13.4 Sub-Surface Drip Irrigation (SDI) ………………………………………....................... 98
13.5 Design of Drip Irrigation in Protected Crops …………………………………………… 99
13.6 Design of Irrigation Systems in Greenhouses ………………………………………… 100
13.7 Drip Irrigation Design for Orchards …………………………………………………….. 100
13.8 Design of Micro-jet and Micro-sprinkler Systems for Orchards ……………………… 110
14 MAINTENANCE OF MICRO IRRIGATION SYSTEMS 117
14.1 General ……………………………………………………………………………………. 117
14.2 Critical Issues in Installation …………………………………………………………….. 117
14.3 Routine Inspection ………………………………………………………........................ 118
14.4 Routine Maintenance ……………………………………………………....................... 119
14.5 Chemical Water Treatments ……………………………………………………………. 122

IV
15 NOMOGRAMS FOR ESTIMATION OF HEAD LOSSES IN PIPES AND
ACCESSORIES 123
16 BIBLIOGRAPHY 128
17 GLOSSARY 133

V
No. LIST OF TABLES Page
6.1 PE (polyethylene) pipes for agriculture…………………………………………………. 28
6.2 LDPE pipe internal diameter and wall thickness………………………………………. 29
6.3 HDPE pipe inner diameter and wall thickness…………………………………………. 29
6.4 PVC pipes for agriculture………………………………………………………………… 30
6.5 Rigid PVC pipes internal diameter and wall thickness………………………………... 30
6.6 Spring actuated pressure regulators……………………………………………………. 34
7.1 Relative clogging potential of drip irrigation systems by water contaminants………. 38
7.2 Characteristics of water passages in drippers (example)…………………………….. 39
7.3 Screen Perforation Examples …………………………………………………………… 40
7.4 Sand particle size and mesh equivalent………………………………………………... 42
7.5 Nominal filter capacity – examples ……………………………………………………... 44
10.1 Pressure and water potential units ……………………………………………………... 57
10.2 Friction Coefficients ……………………………………………………………………… 52
10.3 Multiple outlets factor F ………………………………………………………………….. 62
10.4 Effect of dripper exponent on pressure – flow rate relationships ……………………. 63
10.5 Example of integral drip lateral technical data ………………………………………… 65
10.6 Max. Allowed lateral length for non-compensated line drippers (example) ………. 65
10.7 Allowed lateral length for pressure compensated drippers (example) ……………… 66
13.1 Compensating dripper (compensating pressure threshold – 4 m) data ……………. 89
13.2 Max. Lateral length – m, Model 16012, ID = 13.70 mm, Inlet pressure 3.0 bars ….. 89
13.3 Max. Lateral length – m, Model 16009, ID = 14.20 mm, Inlet pressure 3.0 bars ….. 89
13.4 Non compensating thick wall dripper pressure – flow rate relationship ……………. 90
13.5 Max. Lateral length in non compensating thick wall dripper …………………………. 90
13.6 Non compensating thin wall dripper ……………………………………………………. 91
13.7 . Max. Lateral length in non compensating thin wall dripper ………………………… 91
13.8 The compatible drippers ………………………………………………………………… 92
13.9 Design Form: COMPENSATING RAM DRIPPER 16012, 1.6 L/H, PRESSURE IN INLET 30 m 94
13.10 Thin-wall tape data ……………………………………………………………………….. 97
13.2 (Duplicate) Max. Lateral length – m 16012 compensating dripper laterals………… 103
13.11 Basic data …………………………………………………………………………………. 104
13.12 HEAD LOSSES CALCULATION FORM ………………………………………………. 106
13.13 Head Losses In The Control Head, flow rate 56 m3/h ………………………………... 106
13.14 Head Losses In The Hydraulic Valves On The Sub-Mains flow rate 14 m3/h ……... 107
13.15 Total requested dynamic head …………………………………………………………. 107
13.16 Second alternative – compensating dripper laterals – Basic data ………………….. 108
13.17 Head-loss calculation …………………………………………………………………….. 109
13.18 Total requested dynamic head …………………………………………………………. 109
13.19 The chosen emitter - Non regulated Jet sprayer performance data ………………… 111
13.20 Allowed length of laterals, Emitter type: Jet+ (Red) – lph ……………………………. 112
13.21 Basic data …………………………………………………………………………………. 113
13.22 Head-loss calculation …………………………………………………………………….. 115
13.23 Total requested dynamic head ………………………………………………………….. 115

VI
No. LIST OF FIGURES PAGE
3.1 Point-source (left) and line-source (right) wetting patterns by drippers ……………. 8
3.2 In-line barbed semi-turbulent dripper and in-line integral turbulent dripper ……….. 9
3.3 Evolution of the passageway style …………………………………………………….. 9
3.4 Turbulent flow …………………………………………………………………………….. 9
3.5 Orifice dripper ……………………………………………………………………………. 9
3.6 Vortex dripper …………………………………………………………………………….. 9
3.7 Labyrinth button dripper …………………………………………………………………. 9
3.8 Tape dripper lateral: empty and filled with water ……………………………………... 10
3.9 On-line drippers ………………………………………………………………………….. 10
3.10 Button drippers connector design ……………………………………………………… 10
3.11 Adjustable dripper and flag dripper …………………………………………………… 11
3.12 Flexible diaphragm under pressure ……………………………………………………. 11
3.13 Button and inline PC drippers …………………………………………………………... 11
3.14 Cylindrical PC dripper: water passageway length changed under high pressure … 11
3.15 Flap equipped dripper …………………………………………………………………… 12
3.16 Woodpecker drippers ……………………………………………………………………. 12
3.17 Arrow dripper for greenhouses, nurseries and pot plants …………………………… 13
3.18 Six outlets dripper ……………………………………………………………………….. 13
3.19 Ultra low flow micro-drippers …………………………………………………………… 14
3.20 Integral dripper filters ……………………………………………………………………. 14
3.21 Auto flushing, pressure compensating dripper ……………………………………….. 14
4.1 Micro-emitters ……………………………………………………………………………. 15
4.2 Modular Micro-emitters …………………………………………………………………. 15
4.3 Static micro-jets ………………………………………………………………………….. 16
4.4 Vibrating micro-jet, micro-sprinklers and vortex micro-jet …………………………… 17
4.5 Modular micro-sprinkler …………………………………………………………………. 17
4.6 Bridge micro-sprinkler and bubbler …………………………………………………….. 18
4.7 Water distribution by micro-sprinkler at different flow rates …………………………. 19
4.8 Ray-jet (fan-jet) distribution patterns …………………………………………………... 19
4.9 Micro-emitters mounting alternatives ………………………………………………….. 20
5.1 Typical layout of drip irrigation system ………………………………………………… 22
5.2 Control head ……………………………………………………………………………… 24
5.3 Bucket and drum kits …………………………………………………………………… 25
5.4 Family Drip System (FDS) ……………………………………………………………… 26
5.5 Treadle pump at work and close-up …………………………………………………… 27
6.1 Plastic and metal connectors …………………………………………………………… 31
6.2 Start connectors, plugs and lateral ends ……………………………………………… 32
6.3 Lock fastened connectors ………………………………………………………………. 32
6.4 Connectors and splitters ………………………………………………………………… 32
6.5 Valves ……………………………………………………………………………………... 32
6.6 Hydraulic valve operating principle …………………………………………………….. 33
6.7 Pressure regulators ……………………………………………………………………… 33
6.8 Control valves ……………………………………………………………………………. 34
6.9 Air Relief Valves …………………………………………………………………………. 35
6.10 Atmospheric vacuum breakers …………………………………………………………. 36
6.11 Lateral-end flushing action ……………………………………………………………… 36
6.12 Lateral-end flusher components ……………………………………………………….. 36
7.1 Screen filter ………………………………………………………………………………. 40

VII
7.2 Head losses in clean screen filters …………………………………………………….. 40
7.3 Disc filter ………………………………………………………………………………….. 41
7.4 Media filters ………………………………………………………………………………. 41
7.5 Sand separator working pattern ………………………………………………………... 42
7.6 Hydro-cyclone sand separator – head losses and optimal flow rates ……………… 43
7.7 Automatic flushing of disk filter …………………………………………………………. 45
7.8 High capacity media filter array ………………………………………………………… 46
7.9 Back-flushing of media filters …………………………………………………………… 46
7.10 High capcity automatic filter …………………………………………………………….. 46
7.11 Compact automatic filter ………………………………………………………………… 46
1.12 Treflan impregnated disc filter and its discs stack ……………………………………. 47
8.1 Fertilizer tank ……………………………………………………………………………... 49
8.2 Venturi injector …………………………………………………………………………… 49
8.3 Piston and diaphragm hydraulic pumps ………………………………………………. 50
8.4 No-drain hydraulic pump ………………………………………………………………... 50
8.5 Mixer array ………………………………………………………………………………... 51
8.6 Electric pump …………………………………………………………………………….. 51
8.7 Tandem backflow preventer ……………………………………………………………. 52
9.1 Tensiometers …………………………………………………………………………….. 53
9.2 Watermark granular sensor …………………………………………………………….. 53
9.3 Time domain transmissometry sensor ………………………………………………… 53
9.4 . The pressure bomb …………………………………………………………………….. 54
9.5 Fertilizer and water controller …………………………………………………………... 55
9.6 Integrated monitoring and control ……………………………………………………… 56
10.1 On-line Dripper Connection …………………………………………………………….. 59
10.2 Head losses in hydraulic valves ………………………………………………………... 60
10.3 Relationship between the dripper exponent and lateral length ……………………... 63
10.4 Non-pressure compensating flow-pressure relationships …………………………… 64
10.5 Pressure Compensating dripper flow-pressure relationship ………………………… 64
11.1 Water distribution in the soil: in on-surface drip irrigation. And in SDI …………….. 67
11.2 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 ……………………………………………………………….. 68
11.3 Salt distribution in the wetted volume …………………………………………………. 69
11.4 Leaching of salt into the active root-zone by rain …………………………………….. 69
11.5 Diverse root systems ……………………………………………………………………. 71
11.6 Typical root systems of field crops …………………………………………………….. 71
11.7 Root system in sprinkler irrigation vs. root system in drip irrigation .……………….. 72
12.1 Wetting patterns by drippers in different soil types …………………………………... 74
12.2 Ellipsoid …………………………………………………………………………………… 76
12.3 Drip irrigation layouts in orchards ……………………………………………………… 78
12.4 Dripper layouts in wide-spaced orchards ……………………………………………… 78
12.5 Mechanized deployment of drip laterals ………………………………………………. 80
12.6 Cotton root development ………………………………………………………………... 80
12.7 Potatoes - Laterals on top of hillocks ………………………………………………….. 81
12.8 Wide-scale drip irrigation in greenhouses …………………………………………….. 83
12.9 Drip irrigation of potted plants in greenhouse ………………………………………… 84
12.10 Roadside drip irrigation ………………………………………………………………….. 84
13.1 Different design layouts …………………………………………………………………. 86
13.2 Manifolds save accessories cost ………………………………………………………. 87
13.3 Maize retrievable drip irrigation system layout ……………………………………….. 93

VIII
13.4 SDI layout ………………………………………………………………………………… 98
13.5 thin-wall non-compensating laterals in strawberries – excessive head losses … 99
13.6 Apple orchard – 9.6 Ha ………………………………………………………………….. 101
13.7 Non-compensating on-line drippers flow rate -pressure relationship ………………. 103
13.8 Two of the feasible layouts ………………………………………………………….. 104
13.9 Non- compensating drip system ……………………………………………………….. 105
13.10 Compensating drip system ……………………………………………………………… 108
13.11 Citrus grove - 11.5 ha. …………………………………………………………………... 111
13.12 Micro-jet irrigation system in citrus grove ……………………………………………... 114
14.1 Punch and holder ………………………………………………………………………… 117
14.2 Automatic lateral end flushing valve …………………………………………………… 119
14.3 Vertical stake …………………………………………………………………………….. 120
15.1 Nomogram for calculation of head losses in water flowing in pipes ………………... 123
15.2 Nomogram for calculation of head losses in LDPE pipes. Class designation
relates to the working pressure (PN) in bar …………………………………………… 124
15.3 Nomogram for calculation of head losses in HDPE pipes. The class designation
15.4 Nomogram for calculation of head losses in PVC pipes. The class designation
15.5 Nomogram for calculation of local head losses in valves and other accessories
and fittings ………………………………………………………………………………… 127

1
1. INTRODUCTION
Water scarcity, soaring energy costs, deterioration of agricultural land and
desertification, threaten agricultural development and food production for the fast
growing world population.
Irrigated agriculture increases yield per land unit twice up to ten-fold, compared to
non-irrigated farming.
The principle irrigation technologies are surface irrigation, mechanized irrigation,
sprinkler irrigation and micro irrigation.
Surface irrigation is regarded as the most wasteful technology. Irrigation efficiency is
mostly below 40%. In sprinkler and mechanized irrigation, the efficiency ranges from
60% to 85%. In micro irrigation, the efficiency can attain 90% - 95%.
Micro irrigation is well-suited to harsh environmental conditions. Partial wetting of the
soil volume, superior emission uniformity and a high level of water application control,
facilitate efficient utilization of restricted water resources.
The application of the water in partial, limited soil volume improves the leaching of
salts out of the active root-zone. This raises the upper threshold of permitted salt
content in irrigation water than with full surface wetting technologies. The frequent
applications of water that are mandatory in micro irrigation dilute the soil solution and
keep salt concentration low. Drip irrigation, in particular, minimizes evaporation
losses from the air and soil surface compared with sprinkler, border and furrow
irrigation.
Salinization of irrigated lands is one of the most widespread causes of desertification
(conversion of cultivated land to desert). More than one million hectares of arable
land are lost every year due to salinization. Micro irrigation, particularly drip irrigation,
facilitates the suspension of this process by leaching the accumulating salts out of
the active root-zone. The amount of water needed for adequate salt leaching is
significantly smaller than the leaching requirement in sprinkler, border and furrow
irrigation.
Wide-scale use of drip irrigation commenced in the Middle East, in arid regions in
Israel and disseminated extensively in arid and semi-arid areas all over the world.
The concept of Regulated Deficit Irrigation (RDI) - partial replenishment of the water
consumed by the crop is gaining momentum in arid and semi-arid regions. Under this
irrigation regime, the varying stress sensitivity in different phenological phases is
exploited to reduce water dosage. In the tolerant phases, the soil water deficit is only
partially replenished, maintaining the crop in mild stress that has no serious impact
on yield and the produce quality.
In some crops, salinity can be exploited to improve produce quality. High salt content
in irrigation water improves the produce quality in tomatoes and melons, at the
expense of yield. An economical balance point exists in which the premium for quality
compensates for loss in yield.

2
2. MICRO IRRIGATION
2.1. Introduction
The term micro irrigation refers to irrigation technologies employing water emitters
with tiny apertures that deliver water at a low flow rate. There is no definite distinction
between low volume sprinklers for irrigation and micro-sprinklers used in micro
irrigation, but emitters with flow rates lower than 200 l/h can be regarded as micro
emitters. Micro irrigation is one of the pressurized irrigation technologies alongside
sprinkler irrigation and mechanized irrigation technologies.
Four principal characteristics distinguish micro irrigation from the other pressurized
irrigation technologies:
a. Low flow rate
b. Localized, partial wetting of the soil surface and soil volume while in
sprinkler irrigation in field crops and vegetables the soil surface is wetted
entirely.
c. Frequent water applications are needed due to the limited wetted
volume.
d. Low operating pressure, compared with sprinkler irrigation.
2.2 Micro-emitters Classification
Micro-emitters are classified in two principal groups in respect to water emitting
patterns. The functional objectives of the emitters are distinctive in both groups.
In the first group, water is applied directly to the soil in discrete drops (by drippers) or
as a continuous stream (by bubblers). The objective of the water passageways is to
maximize pressure dissipation, to approach atmospheric pressure in the emitter
outlet.
In the second group, water is conveyed through the air and applied to the soil as
spray, mist or multiple discrete jets. Pressure dissipation is kept to a minimum in
order to enable the water to be adequately spattered on the desired surface area.
Each group is further subdivided in regard to the working patterns:
2.2.1. Emitters for direct application to the soil:
2.2.1.1 Drippers
2.2.1.2 Bubblers
2.2.2. Emitters for water application through the air:
2.2.2.1 Static emitters
2.2.2.1.1 Sprayers
2.2.2.1.2 Ray microjets (fan-jets)
2.2.2.1.3. Misters and foggers
2.2.2.2 Vibrating emitters
2.2.2.3 Rotating emitters

3
2.2.2.3.1. Micro sprinklers
2.2.2.3.2. Rotators
2.2.2.3.3. Spinners
Micro irrigation holds four obvious advantages over most other irrigation
technologies:
a. High efficiency in water application.
b. Improved plant nutrition management.
c. Better salinity handling.
d. Low energy requirement compared with sprinkler and mechanized
irrigation.
The basic planning and design procedures are similar in the two micro irrigation
technologies. Since drip irrigation is the most widespread technology, it receives
more coverage than spray technology in this publication.
2.3. Terminology
Certain terms relating to irrigation have different interpretations in micro irrigation
than in conventional sprinkler irrigation.
2.3.1. Application Rate
In full surface area wetting technologies such as sprinkler or border irrigation, the
application rate is designated as the volume of water applied over area unit during a
time unit. The application rate is expressed in units of l/m2
/hour, m3
/ha/hour or
mm/hour. The last unit indicates the depth of the applied water volume equally
spread on the irrigated area. E.g.: 1 mm water depth over 1 m2
area (1,000,000 mm2
)
is: 1 mm × 1,000,000 mm2
= 1,000,000 mm3
(micro liters). 1,000,000 micro liters =
1000 milliliters = 1 liter/1 m2
. Since 1 ha consists of 10,000 m2
, 1mm water depth =
10,000 l/ha = 10 m3
/ha.
In localized micro irrigation, the water does not spread evenly on the soil surface.
The term Irrigation Rate (IR) designates a virtual value. The applied water quantity
per hour over the irrigated area is addressed as if coverage is uniform.
The virtual irrigation rate per single emitter will be its flow rate over spacing between
emitters.
Example:
Emitter flow rate: 2 l/h
Spacing 3 × 0.5 m
Irrigation Rate = 2 / (3 × 0.5) = 1.333 l/m/h = 13.33 m3
/ha/h
2.3.2. Water Distribution
The water that spread unevenly on the soil surface and in the soil volume makes it
impractical to consider Distribution Uniformity the same as in sprinkler and border
irrigation. The wetted volume by a single emitter has variable moisture levels as a
function of distance from emitter, soil properties and water dose. Hence the
uniformity of water distribution in micro irrigation is expressed differently than in
sprinkler irrigation. The common term is Emission Uniformity (EU) that indicates the
variance between emitters in a representative sample. The calculation for EU is the
same as the calculation for DU but it relates to variance between emitters and not to
application to area unit.

4
2.3.3. Distribution of Chemicals
The distribution of dissolved chemicals (salts, nutrition elements) in micro irrigation
has also different pattern than in other irrigation methods. This pattern is beneficial
for nutrition and salt management but obliges strict precautions to be taken in acute
climatic events like heat spells and early rains after a dry period.
2.4. Water Distribution Uniformity
2.4.1. Irrigation Efficiency
Irrigation Efficiency (IE) is an important parameter for the evaluation of irrigation
excellence.
(Eq. 2.1)
Water beneficially used is the sum of the water amounts applied for the
replenishment of water used for evapo-transpiration from the plant and the soil
surface, for fertilizer and pesticide application, for salt leaching, for frost protection
and for crop cooling.
Micro irrigation facilitates the application of even volume of water to every plant in the
irrigated plot. This requires suitable spacing between laterals and emitters as well as
an appropriate pressure regime.
Application Uniformity can be expressed by different indices. A uniformity of 100%
means that each point within the plot area gets exactly the same amount of irrigation
water. When uniformity is low, certain sections of the plot receive less water than
others. In order for those sections to receive sufficient amount of water, extra water
amount has to be applied to the plot as a whole. As the application uniformity is
lower, the required amount of extra water will be greater. Application uniformity is
particularly important with drip irrigation systems, due to the cumulative nature of
non-uniformity embodied in factors that determine the dripper's flow rate.
2.4.2. Distribution Uniformity
A common index of application uniformity is DU (Distribution Uniformity). For
calculating this value, the flow rate of a representative sample (40 - 100 emitters
randomly selected in different sections of the irrigated plot) is measured.
Q25%
------------------
DU = 100 ×
Qn
(Eq. 2.2)
Where: Q25% is the average flow rate of 25% of the emitters with the lowest flow rate,
and Qn is the average flow rate of all the sampled emitters.
DU significance:
>87% - excellent distribution uniformity
75% - 87% - good uniformity
62% - 75% - acceptable
<62% - unacceptable.
Variability in the flow rate depends on the pressure regime, the manufacturing
variance of the emitters and partial emitter clogging.
Water beneficially used
--------------------------------------------------IE =
Total applied water

5
2.4.3. Manufacturer’s Coefficient of Variation (Cvm)
No two emitters can be identically manufactured; there will be always a certain
variation. The flow rate uniformity of new emitters is evaluated with the
Manufacturing Coefficient of Variation (Cvm).
Cvm indicates the variability in the flow rate of a random sample of a given emitter
model, just off the production line before any field operation or degradation has taken
place.
The flow rate variation in manufacturing is determined statistically. Randomly
selected emitter samples or a lateral segment are tested under constant pressure.
The Cvm is defined as the standard deviation over the average flow rate of a sample
of emitters. It is expressed as a decimal fraction or percentage. (0.01 = 1%)
According to the formula:
Sdm
--------Cvm =
Xm
(Eq. 2.3)
Where: Cvm = manufacturer coefficient of variation,
Sdm = standard deviation,
Xm = mean flow rate.
A Cvm of 0.1 (10%) means normal distribution (a “bell shaped” curve), where 68 % of
all emitter flow rates are more or less within 10% deviation from the mean flow rate.
The emitter design, materials used in production, and manufacturing precision
determine the variance in any particular emitter type.
The standard ranking of variability is as follows:
a. For point source emitters:
Cvm <0.05 - excellent
0.05 - 0.07 – average
0.07 - 0.11 – marginal
0.11 – 0.15 – poor
>0.15 – unacceptable
With recent improvements in manufacturing technology, most emitters have Cvm <
0.10. Pressure compensating emitters have a somewhat higher Cvm than non-
compensating labyrinth path emitters, due to the cumulative variability of the
passageway and the compensating mechanism.
b. For line source emitters (comparison of 1 m length segments):
Cvm <0.10 - good
0.10 – 0.20 – average
> 0.20 – marginal to unacceptable
2.4.4. Emission Uniformity
The Emission Uniformity (EU) conforms to Distribution Uniformity.
A controversy still exists about whether or not to consider Cvm to determine Emission
Uniformity when designing irrigation systems.
The stringent attitude claims that Cvm is one of the cumulative factors that determine
the uniformity of water distribution and has to be taken into account.

6
In this case, Emission Uniformity will be calculated using the following formula:
Where
EU = the design Emission Uniformity, %.
n = for a point-source emitter in a perennial crop, the number of emitters per plant; for
a line-source emitter in an annual or perennial row crop, either the horizontal rooting
diameter of the plants, divided by the same unit length of lateral line used to calculate
Cvm or 1, which of these variables that is greater.
Cvm = manufacturer’s coefficient of variation.
qm = minimum emitter flow rate in the sample, l/h.
qa = average or design emitter flow rate for the related sample, l/h.
The lenient attitude claims that since emitters with a dissimilar flow rate are randomly
located, the Cvm has to be ignored in evaluating Emission Uniformity in the design
process.
It has to be emphasized that the Design Emission Uniformity is relevant only for
new equipment before field operation. Once the system has been operated, there is
degradation of the Emission Uniformity due to full or partial clogging of emitters,
deformation of emitters and compensating membranes and damage to hoses and
tapes by environmental and mechanical factors. High-level maintenance, routine
periodical inspections and corrective measures are required to lessen the
degradation in water distribution uniformity within an irrigated plot over the long term.
2.4.5. Flow Variation of Emitters on the Lateral
This compares maximum and minimum emitter flow rates along a single lateral.
qvar = (qmax - qmin)/qmax (Eq. 2.5)
or
qvar = 1 – (qmin / qmax) (Eq 2.6)
Where qmax is the maximum emitter flow rate, qmin is the minimum emitter flow rate,
and qvar is the emitter flow rate variation. It is assumed that the manufacturer's emitter
flow variation follows normal distribution so that the mean value plus two standard
deviations is considered as the maximum flow rate, and the mean value minus two
standard deviations is considered as the minimum emitter flow rate. This range
covers over 95% of the emitter flow rates measured in the tests.
Relating test results to the manufacturer’s Cvm indicates that with a manufacturing
Cvm of 0.05 = 5%, the difference between maximum and minimum flow rates on the
lateral may be 15%.
1.27Cvm qm
---------------- --------EU =100[1.0
√n
]qa
(Eq. 2.4)

7
3. DRIPPERS - STRUCTURE AND FUNCTION
3.1. Introduction
Drippers, the core of the drip irrigation system, are small water emitters made of
plastic materials. The design and production of high quality drippers is comprised of
delicate and complicated processes.
The basic indispensable attributes of a dripper:
a. Low flow rate (discharge): 0.5 – 8 liter per hour (l/h).
b. Low vulnerability to clogging.
c. Low production cost and durability.
Attaining low flow rate necessitates a high extent of pressure dissipation. The flow
rate is determined by the pattern and dimensions of the dripper’s 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 plugging by suspended solid particles and
chemical precipitates.
Since the dissipated water pressure en route to the dripper's outlet is a key factor in
determining its flow rate, sophisticated passageway patterns have been developed
for high pressure dissipation.
3.2. Types of Drip Systems
Drip systems can be classified in respect to a variety of parameters:
3.2.1 Spatial Placement of Laterals
3.2.1.1. On-Surface Drip Irrigation
The dominant drip technology is on-surface drip irrigation. In this arrangement,
monitoring and control of the drippers' performance is convenient and effective. On
the other hand, the laterals are prone to mechanical damage and degradation by
solar radiation and may interfere with farming activity. In annuals, seasonal
deployment and retrieval of the laterals is obligatory and annoying. In vineyards, kiwi
plantations and palmetta-shaped deciduous orchards, laterals are hanged on trellises
in order to relieve monitoring of dripper function and minimize mechanical damage.
3.2.1.2. Subsurface Drip Irrigation (SDI)
SDI has gathered momentum over the last two decades.
3.2.1.2.1. SDI Main Advantages:
a. Negligible interference with farm activity
b. Elimination of mechanical damage to laterals
c. Decreased weed infestation
d. Elimination of runoff and evaporation from soil surface
e. Improved uptake of nutrition elements by the roots, notably phosphorous.
3.2.1.2.2. SDI Main Disadvantages:
a. High installation costs
b. Plugging hazard by intruding roots and sucked-in soil particles
c. Inconvenience in monitoring the performance of drippers and laterals
d. Strict maintenance is mandatory

8
3.2.2. Layout of Water Outlets along the Lateral
Two typical layouts of drippers on laterals determine the water distribution pattern in
the soil.
3.2.2.1. Point Sources
In this layout, drippers are mounted or inserted along the laterals at length intervals
that create a discrete wetted soil volume by each emitter, without overlapping. In
orchard irrigation and in widely spaced annuals, thick walled hose laterals are
favored.
Fig. 3.1. Point-source (left) and line-source (right) wetting patterns
3.2.2.2. Line Sources
Drippers are densely positioned along the lateral, ensuring overlapping of the wetted
soil volumes by adjacent drippers. This layout is typical in tape design and is the
favored choice for densely grown annual crops.
3.3. Lateral Type
3.3.1. Thick-Walled Hoses
Thick-walled hoses, used as drip laterals are made of Low Density Polyethylene
(LDPE) of 12 – 25 mm external diameter and 1 – 2 mm wall thickness. The discrete
drippers are mounted on-line or inserted inline, 10 – 100 cm apart. The normal
working pressure (PN) is 1 – 4 bar (10 – 40 m).
3.3.2. Thin-Walled Laterals
Thin-walled laterals may be manufactured as hoses or tapes. The thin-walled hose
keeps its cylindrical cross section also when it is empty while the tape lies flat when it
is not filled with water. The tapes are also made of LDPE. However, the wall
thickness is only 0.1 – 0.9 mm and the PN is 0.1 – 1 bar (1 – 10 m). Laterals may be
fitted with discrete molded or inserted drippers. Some tapes have contiguous
pressure dissipating passageways as integral components.
3.4. Water Passageway Structure and Characteristics
3.4.1. Long Laminar or Semi-turbulent Path
The water flows through a narrow, long micro-tube. The micro-tube may be long
(spaghetti) or a built-in spiral in a capsulation. Water flow is laminar in the spaghetti
and semi turbulent in the built-in spiral. The friction of water with the tube walls plus
the internal friction between water molecules results in pressure dissipation. The flow
rate of laminar-flow drippers is specifically sensitive to changes in pressure. The long

9
water path and low flow velocity bring about deposition of chemical precipitates that
alter the dripper's flow rate. In extreme cases, the emitter is fully plugged.
Fig. 3.2. In-line barbed semi-turbulent dripper (left) and in-line integral turbulent dripper (right)
3.4.2. Labyrinth Path
The water flows along a
labyrinth in which the flow
direction changes abruptly.
The recurrent changes in
direction result in turbulent
flow, high-energy losses and
decreased flow rate. The
labyrinth passageway is wider
and shorter than the laminar
path of the same flow rate. The
turbulent flow flushes the
corners of the twisted water
path, decreasing clogging
events. The flow rate in a
labyrinth dripper is less
affected by changes in
pressure, compared with
laminar flow. The short path
facilitates fabrication of
smaller, cheaper drippers.
3.4.3. Zigzag (toothed) Path
This passageway form has higher pressure dissipation and better self-cleaning
attributes. Enhanced version of the toothed passageway - TurboNet - allows for
shorter, wider water passageways.
Preliminary
laminar
design
Semi
turbulent
dripper
Labyrinth
passageway
Toothed
(zigzag)
passageway
TurboNet
passageway
Fig. 3.3. Evolution of the passageway style Courtesy “Netafim”
Fig. 3.4. Turbulent flow from "DIS" brochure
Fig. 3.5. Orifice dripper
Adapted from Karmeli & Keller, 1975
Fig. 3.6. Vortex dripper
Adapted from Karmeli & Keller, 1975
Fig. 3.7. Labyrinth button dripper
Courtesy "Netafim"

10
3.4.4. Vortex Drippers
In vortex drippers, water enters tangentially into a circular chamber, creating a spiral
whirlpool that generates high head losses along a relatively short path. This allows
for a wide-outlet orifice that decreases clogging hazard.
3.4.5. Orifice Drippers
Pressure dissipation occurs at a tiny inlet in the bottom of the dripper, rendering it
prone to plugging.
3.4.6. . Tape Laterals
Trickling tapes are made of thin walled plastic tubes. When empty, the pipe lies flat. It
gets a cylindrical cross section when filled with water. Water emission can take place
directly through tiny perforations in the wall or through molded labyrinth
passageways. The first-mentioned design is prone to partial or full clogging of the
perforations and its emission uniformity degrades with time.
Fig. 3.8. Tape trickling lateral: empty (left) and filled with water (right) Adapted from "T-Tape" brochure
3.5. Position on Lateral
Drippers can be mounted externally on the lateral (on-line), or inserted in-line.
Fig. 3.9. On-line drippers Courtesy "Netafim"
3.5.1. On-Line Mounted Drippers
On-line drippers are mounted through
punched holes. Drippers can be added to the
laterals with time to answer changes in crop
development and water requirements.
The dripper has a threaded or barbed joint
that is screwed or inserted into thick-wall
hoses. Because it protrudes from the lateral,
it is prone to damage in delivery, installation
and retrieval. Fig. 3.10. Button drippers connector design

11
3.5.2. In-Line Inserted Drippers
In-line drippers leave the outer face of the lateral smooth. Two versions are available:
3.5.2.1. Built-in Drippers
The drippers are fused into the lateral during its extrusion process.
3.5.2.2. Barbed Drippers
Each dripper joins two segments of the lateral.
3.6. Dedicated Drippers
3.6.1. Adjustable Drippers
3.6.2. Flag Emitters
The dripper has a twisting locker that facilitates
cleansing of clogged drippers while water continues
to flow in the lateral.
3.6.3. Pressure Compensating (PC) Drippers
The flow rate of compensating emitters remains uniform provided the pressure in
dripper's inlet is kept above a given minimum threshold. The compensating
mechanism narrows or lengthens the internal water passageway as the pressure
rises, adjusting the friction head losses that keep the flow rate constant.
3.6.3.1. Flexible Membrane above
Water Path
As the pressure above the diaphragm
rises, the water passageway below the
diaphragm narrows, increasing head
losses and decreasing the flow rate.
3.6.3.2. Changing the Length of the
Water Flow Path
Pressure compensation is accomplished by changing the effective length of the water
path. The higher the pressure the longer the effective passageway, rendering higher
head loss.
Fig. 3.14. Cylindrical PC dripper: water passageway lengthened under high pressure
From "Mezerplas" brochure
Fig. 3.13. Button and inline PC drippers
Courtesy "Netafim"
Fig. 3.12. Flexible diaphragm under
pressure

12
3.6.4. Non-Leakage (No Drain) Drippers
Draining of drip laterals after water shutdown promotes accumulation of precipitates
at the bottom of the laterals and in the dripper's water passageway. Additionally, time
elapses from the renewal of water supply until the laterals are filled with water and
the desired working pressure builds-up. During this interval, the flow rate of the initial
drippers in the lateral is significantly higher than that of the drippers at the distal end.
Frequent small water applications, makes this time segment of uneven emission a
significant part of the irrigation time length, decreasing application uniformity.
These results generate a substantial variance in water dosage between the initial and
the distal ends of the laterals and in the irrigated plot as a whole.
Non-leakage drippers eliminate drain of the laterals
after water shutdown by sealing the dripper's outlet
as the pressure drops. This facilitates rapid
pressure build-up in the laterals at the start of
irrigation.
3.6.5. Flap Equipped Drippers
Drippers equipped with a flap on the water outlet
eliminate suction of small soil particles into the dripper by back siphonage at
shutdown, as well as the intrusion of roots into drip laterals in subsurface drip
systems.
3.6.6. Woodpecker Drippers
These drippers are used in areas prone to
woodpecker activity. The birds, while
looking for water, drill holes in the laterals.
Preventive action is taken by burying
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.
3.6.7. Trifluraline 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 the installation of the subsurface
laterals, small amounts of the herbicide are released with each water application into
the soil adjacent to the dripper, sterilizing its immediate vicinity. Drippers
impregnated with Trifluraline can substitute routine Treflan application for up to 15
years.
Fig. 3.15. Flap equipped dripper
Bug cover Woodpecker
Fig. 3.16. Woodpecker drippers

13
3.6.8. Arrow Drippers
Arrow dippers are used for the irrigation of potted plants. The stake-styled dripper is
inserted into the growing bed. A high capacity built-in filter and efficient zigzag
turbulent water passageway keep the tiny dripper unplugged and reliable for long-
term use.
3.6.9. Multi-Outlet Drippers
Each dripper has 2 – 12 outlets onto which small diameter
micro-tubes are connected. The drippers are used mostly in
landscaping and for irrigation of potted plants.
3.6.10. Ultra Low-Flow Drippers
The exceptionally low water
emission rates of 0.1 – 0.3 l/h per
dripper alters the water
distribution pattern in the soil and
other growing media. The water-
to-air ratio in the wetted bed
volume is altered in favor of the
air. Water horizontal movement is
more pronounced than with
drippers of conventional flow rate.
In this technology, water can be
applied to shallow rooted plants
with minimized drainage beneath
the root-zone.
Due to the narrow water
passageways and low flow velocity, these tiny drippers are prone to clogging.
Fig. 3.17. Arrow dripper for greenhouses, nurseries and pot plants Courtesy "Netafim"
Fig. 3.18. Six outlets
dripper
Fig. 3.19. Ultra low flow micro-drippers
Adapted from "Plastro" brochure

14
The minute flow rate is achieved in two techniques:
a. A conventional button dripper releases water into a secondary micro-tube with 10
– 30 molded or inserted micro-drippers.
b. Water is applied in pulses through conventional drip laterals. The pulses are
created by the irrigation controller or by dedicated pulsators. To correspond with the
short pulses and long time intervals, drippers should be of the non-leakage type.
3.7. Integral Filtration in Drippers
Modern high quality drippers are fitted with built-in integral filters. The filtering area
increased significantly in the new models to ensure long-term high performance with
reduced clogging.
Other anti-clogging means are:
a. Dual water inlets and outlets per dripper.
b. The barbs of on-line drippers protrude deep into the lateral, keeping the water inlet
away from the dirt that accumulates on the lateral's walls.
Anti-siphon devices such as the abovementioned flaps also decrease clogging
occurrence.
3.8. Auto Flushing Mechanisms
Certain compensating drippers are fitted with unique flexible diaphragms for
releasing the debris that clog the dripper. When a solid particle blocks the water path,
the diaphragm arches to widen the passageway and the clogging object is released.
Static state Pressure compensation Flushing
Fig. 3.21. Auto flushing, pressure compensating dripper Courtesy "Netafim"

15
4. MICRO-JETS AND MICRO-SPRINKLERS
4.1. Introduction
Micro emitters that disperse water through the air are used extensively in orchard
irrigation. Unlike sprinkler irrigation used in field crops and vegetables where water is
distributed evenly over the entire irrigated area, in orchard irrigation, full soil surface
coverage and even distribution of water is unattainable and is not necessary. The
objective of orchard irrigation is to deliver equal amounts of water to each tree and to
distribute it in compliance with the root system distribution pattern in the soil.
Under-canopy irrigation is common in orchard
irrigation. It can be carried out by low-volume, low-
angle mini sprinklers as well as by micro-sprinklers,
micro-jets, sprayers, drippers and bubblers.
Recently, the use of micro-sprinklers had been
extended to irrigation of vegetables and field crops.
Micro-emitters built of rigid plastic materials are
much smaller and cheaper than conventional
sprinklers.
Four emitter types are available:
a. Static micro-jets
b. Micro-jets with vibrating deflector
c. Micro-sprinklers - spinners and rotators
d. Vortex Emitters
The operating pressure is 10 – 30 m., somewhat higher than in drip systems. The
water distribution range at a given pressure depends on the nozzle geometry,
emission pattern flow rate and water pressure (head).
Many types of micro-sprinklers are modular. Components are interchangeable and
facilitate low cost modification of flow rate, droplet size, distribution pattern and
range. Changing the deflector and nozzle makes the difference.
Fig. 4.2. Modular Micro-emitters Courtesy "Naan-Dan"
Fig. 4.1 Micro-emitters

16
Deflectors in diverse configurations allow sectorial coverage from 450
to 3600
.
4.2. Static Micro-jets
Static micro-jets have no moving components and are classified into three groups:
4.2.1. Sprayers – the water stream is fragmented into tiny droplets by means of a
static deflector. Water is distributed in a relatively short range and the tiny drops are
wind sensitive.
4.2.2. Misters and Foggers – water droplets are smaller than in sprayers. Spread
range is shorter. Wind sensitivity and evaporation losses are higher than in sprayers.
This type is mostly used to increase the humidity in greenhouses and poultry coops,
as well as for frost protection in orchards.
4.2.3. Ray-Jets (Fan-Jets) – the water stream is spitted into 4 – 20 discrete jets.
The range is extended and wind sensitivity is reduced.
Static sprayer Mister Fogger Ray-jet
Fig. 4.3. Static micro-jets
4.3. Vibrating Micro-jets
Water ejected from a circular orifice strikes a deflector and triggers it to vibrate. The
vibration of the deflector creates larger drops than in sprayers, increases the
distribution range and reduces evaporation and wind sensitivity.
4.4. Micro-sprinklers
4.4.1. Rotators are manufactured in different configurations. The central shaft with
the nozzle is static. The water jet hits a rotating deflector that distributes water in
larger area than the vibrating emitters.
4.4.2. Spinners - the nozzle rotates and further increases the jet range.
The movement of components in micro-sprinklers increases their sensitivity to the
interference of factors like weeds, precipitates and splashed soil particles. It also
accelerates wear and tear. The damage hazard from herbicide sprayer booms and
other tillage equipment is particularly increased during harvest operations.
4.5. Vortex Emitters
These emitters have no moving parts. The water revolves in a circular vortex
chamber that delivers a low flow rate through a relatively large opening that reduces

17
the clogging hazard. The area wetted by this emitter is smaller than in other emitter
types.
Vibrating sprayer Rotator Spinner Vortex sprayer
Fig. 4.4. Vibrating micro-jet, micro-sprinklers and vortex micro-jet
Micro-sprinkler components Interchangeable components
Fig. 4.5. Modular micro-sprinkler
Pressure compensating and flow regulated micro-emitters are particularly suitable for
irrigating steep sloping plots.
Micro-sprinkler systems require a higher volume of water supply compared to on-
surface or buried drip systems.
4.6. Bubblers
In Bubblers, as with drippers, the water pressure dissipates almost fully on its way to
the outlet, but the discharge is much higher: 20 – 200 l/h. The water flows from the

18
bubbler along its stake or spreads adjacent to it. The pressure is dissipated through
diaphragms and small orifices.
Bubblers may be pressure compensating.
Multiple outlets are available. In some
cases the use of bubblers requires the
excavation of small basins around the
emitter to prevent runoff.
Micro-emitters are mostly connected to
the laterals by means of a plastic micro
tube. They are mounted on a stake or a
rod to stabilize their vertical position at
10 - 25 cm above ground level.
Threaded micro-emitters are installed
on 1
/2
"
– 3
/4" rigid PVC risers. Barb
micro-emitters can be mounted directly
on the lateral. In greenhouses, micro-
emitters may be installed upside down
for overhead irrigation and misting.
Weights are hung to stabilize them
vertically.
Bridge type micro-emitters provide
improved support to the rotating spinner
or deflector, but the vertical supports of
the bridge creates dry sectors behind
them.
Micro-emitters are as prone to clogging
as drippers, but when clogging occurs it
is quickly noticed and easily cleaned.
Some emitters are equipped with a
small integral valve to enable local water shutdown during the cleaning process.
Some types of micro-sprinklers are prone to clogging by the eggs and excretions of
spiders, ants and other insects. Insect-proof devices have been developed to prevent
these obstructions. Ant and bug caps may be added to discourage ants and other
insects from intruding into the system. Spiders are capable of tying up spinners and
halt their rotation. Micro-sprinkler operation can be disturbed by sand that is splashed
upward from the soil surface when hit by droplets from adjacent emitters.
Plugs that are not removed on time in orchards that employ one emitter per tree may
result in lower yields and reduced produce quality.
4.6. Water Distribution Patterns
The emitter’s water distribution pattern depends on its outlet (nozzle) and deflector
geometry, trajectory angle, droplets size, pressure and flow rate. The higher the
trajectory angle (up to 450
) and the larger the droplet size and flow rate, the larger will
be the wetting diameter. The patterns of water distribution and wetting depth in the
wetted area vary with the emitter type. In some emitters the wetting pattern is
triangular. These emitters are suitable for overlapping and full wetting of the soil
Unilateral bridge
Bi-lateral bridge Bubbler
Fig. 4.6. Bridge micro-sprinkler and bubbler

19
surface. In some emitters the deeper wetting depth is adjacent to the emitter while in
others it is uniform in most of the wetted area.
Fig. 4.7. Water distribution by micro-sprinkler at different flow rates (example)
Fig. 4.8. Ray-jet (fan-jet) distribution patterns From "Bowsmith" Brochure
4.7. Pressure Compensation
Like drippers, micro-sprinklers and micro-jets can be pressure compensating. That
facilitates longer laterals and uniform application in harsh topographic conditions.

20
4.8. Emitter Mounting
Emitters can be mounted directly on the lateral attached by a barbed or threaded
protrusion. The preferred connection to the lateral is by means of a small diameter
micro-tube. The vertical position is secured by a stake, stabilizing rod or stabilizing
tube. The emitter is raised 10 – 25 cm above soil surface to prevent halt of rotation of
the moving parts by weed interference and splashed soil particles. The micro-tubes
are 50 – 100 cm long and 4 – 8 mm in diameter. Diameter of 6 - 8 mm is preferred for
emitter flow rates over 60 l/h and when the micro-tube length is over 60 cm, to
prevent excessive head losses.
In greenhouses, micro-sprinklers, misters and foggers are frequently used to
increase the relative humidity and lower the temperature of the ambient atmosphere.
The misters and the foggers emit tiny droplets and are operated intermittently in
pulses. These emitters are often mounted upside-down with the trajectory angle
slanted downwards, in order to avoid hitting the glass or plastic ceiling.
Sprayer on
stake
Upside-down misters
with stabilizing tubes
Micro-sprinkler on rod Upside-down
Micro-sprinkler
Fig. 4.9. Micro-emitters mounting alternatives

21
5. THE MICRO IRRIGATION SYSTEM
Water emitters are the end devices of the micro irrigation system which is composed
of a variety of interconnected components.
The constituents of the system are classified into six principal categories:
a. Water Source: river, lake, reservoir, well, or connection to a public, commercial
or cooperative water supply network. Micro irrigation is a pressurized irrigation
technology in which water is delivered from the source by increasing its internal
energy (pressure) by pumping.
b. Delivery System: Mainline, submains and manifolds (feeder pipes).
c. Emitter Laterals
d. Control Devices: Valves, flow meters, pressure and flow regulators, automation
equipment, backflow preventers, vacuum and air release valves, etc.
e. Filtration Devices
f. Chemical Injectors: for introduction of plant nutrients and water treatment
agents into the irrigation water.
5.1 The Water source
5.1.1. The Water Supply Control Head
There are two alternative sources of water supply:
a. Direct withdrawal from an on-surface source (such as a 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.
If pumping is needed, the pump will be chosen according to the required flow rate
and pressure in the irrigating system.
When connected to a water supply network, the diameter of the connection, main
valve and the delivering line should correspond with the planned flow rate and
working pressure in the irrigated area.
5.2. The Delivery System
5.2.1. Mainlines for Water Delivery and Distribution: Pipes are made of PVC
or polyethylene (PE). Ordinary PVC pipes have not UV protection and should be
installed underground. Recently, unplasticized PVC (UPVC) pipes are manufactured
with reduced sensitivity to UV and better endurance than common PVC pipes. PE
(polyethylene) pipes can be installed inside or above ground, as they are
impregnated with carbon black that provides counter UV protection. The pipes’
nominal working pressure (PN) has to be higher than that of the drip laterals,
particularly if the system has to withstand pressure fluctuations with while valves are
closed. The common PN of delivery and distribution mainlines is 6 – 8 bar (60 – 80 m
dynamic head).

22
5.2.2. Submains
Submains are installed underground (PVC or PE) or above ground (PE only). In
retrievable drip systems in annual crops, above-ground pipes are made of PE,
aluminum or vinyl “lay flat” hose.
5.2.3. Manifolds
In certain circumstances, when rows are very long or in harsh topography, sub-
division of the plot by submains is insufficient. In these cases secondary partition is
carried out by manifolds. Manifolds are used also to simplify operation and to lower
accessories costs.
Fig. 5.1. Typical layout of micro irrigation system
5.3. Laterals
Laterals are made mostly of LDPE (Low Density Polyethylene). PVC laterals are
used on a limited scale. The laterals may be laid on the soil surface or underground.
Shallow burying of drip laterals, 5 – 10 cm below soil surface is suitable to vegetables
grown on hillocks or under plastic mulch.
5.4. Control and Monitoring Devices
5.4.1. Valves and Gauges
5.4.1.1. Manual or automatic valves are used for the opening and shutdown of
water and for splitting the irrigated area into sectors. Water-meters (flow meters) are
used to measure the amount of water delivered.
5.4.1.2. Pressure regulators prevent excessive pressure beyond the working
pressure of the system.
5.4.1.3. Check valves and backflow preventers are required when fertilizers or
other chemicals are injected into the irrigation system, if the irrigation system is
connected to potable water supply network.

23
5.4.1.4. Air-release/relief valves are installed in the higher points of the system to
eliminate air flow in the pipes. High air content in the pipes may interfere with water
flow, increase friction with pipe walls, distort water measurement and may cause
water hammer and pipe burst.
5.4.1.5. Vacuum breakers prevent the collapse of pipes in steep slopes and drip
laterals in Sub-surface Drip Irrigation (SDI) systems. In SDI they also eliminate the
suction of soil particles into the drippers after shutdown of the water supply.
5.4.2. Filtration
In micro emitters, the narrow water passageways are susceptible to clogging by
suspended matter and chemicals that precipitate from the irrigation water. Clogging
can be eliminated by:
a. Preliminary separation of suspended solid particles by settling ponds, settling
tanks and sand separators.
b. Complimentary chemical treatments for decomposition of suspended organic
matter; to hinder the development of slime by microorganisms; to prevent
chemical precipitates deposition and to dissolve previous deposited
precipitates.
c. Filtration of the irrigation water.
Filtration devices are usually installed at the control head. If the irrigation water is
heavily contaminated, secondary control filters are installed at the sectorial valves.
Filters should be flushed and cleaned routinely. Flushing can be done manually or
automatically. Automatic back-flushing of media filters is performed with filtered
water, hence, the filters are installed in arrays of two or more units and the filters are
flushed in sequence one after another.
5.4.3. Chemical Injectors
Three categories of chemicals are injected into irrigation systems: fertilizers,
pesticides, and anti-clogging agents.
• Fertilizers are the most commonly injected chemicals; the capacity to “spoon-
feed” the crop with nutrients, increases yields with micro irrigation.
• Systemic pesticides are injected into drip irrigation systems to control insects
and protect plants from a variety of diseases.
• Chemicals that clean drippers or prevent dripper clogging.
Chlorine is used to kill algae and different microorganisms and to decompose organic
matter, while acids are used to reduce water pH and dissolve precipitates.
The different types of injectors are described in the chapter on fertigation.

24
Fig. 5.2. Control head Courtesy " Netafim"
5.5. Sub-surface Drip Irrigation (SDI)
Since the early eighties, sub-surface drip irrigation technology has gained
momentum.
Advantages of SDI:
a. Elimination of interference with farming activities
b. Reduced soil compaction
c. Elimination the burden of laying and retrieving laterals in annual crops
d. Protection of laterals from mechanical and environmental damage
e. Water conservation, Avoidance of direct evaporation from soil surface
f. Decreased weed infestation
g. Improved nutrient application efficiency
h. suitable for utilization of reclaimed water for irrigation of edible crops
Limitations of SDI:
a. High initial cost
b. Inconvenient monitoring of water application and expensive maintenance
c. Increased emitter clogging hazard by penetrating roots and sucked soil
particles
d. Water "surfacing" – unintended soil surface wetting by capillary upward water
movement
e. High water loss by deep percolation in cracking soils
f. Germination irrigation has to be with sprinklers in some crops
g. Limits the depth of land tillage
h. difficulties with crop rotation
i. Prone to damage by rodents

25
In Sub-Surface Drip Irrigation (SDI), drip laterals are buried 10 – 50 cm below the soil
surface.
5.6. Low-cost Drip Irrigation Systems
In many developing countries, irrigation is used for growing fruit and vegetables for
own consumption in family-owned gardens, some of which on area of 20 – 500 m2
.
These gardens are mostly furrow-irrigated with water drawn from shallow wells,
rivers, lakes and reservoirs; either by hand, animals or by small motor-driven pumps.
In the last decade, productivity has impressively improved by replacement of furrow
irrigation with small scale systems of drip irrigation.
Conventional drip technology is not suitable for these small gardens. It is expensive
and out of the reach of small producers. Cheap low-pressure drip systems were
developed for these small-holders by "Netafim" and "Ein Tal" of Israel, "Watermatics"
of Mr. Chapin in the USA and Africa, and "IDE International" in the USA and India.
Local simplified versions were also developed in other developing countries.
"Watermatics" supplies bucket-kits and drum-kits. The bucket kit is comprised of an
ordinary bucket, a filter, delivery tubes and two 15-m long drip laterals. The bucket is
hung at height of one meter above ground, and the two laterals deliver water by
gravity to the garden. The irrigated area is 25 – 30 m2
. The bucket-kits cost six
dollars each to non-profit organizations and to individual farmers.
Super Bucket Kit provides drip irrigation for 10 rows, 10 meters long each, covering
100 m2
. This area can be watered from a 250-l container filled once a day.
Fig. 5.3. Bucket kit (left) and drum kit (right) From "IDE International" Brochure
"IDE" supplies a five-dollar starter kit that irrigates 25 m2
with one lateral and with two
laterals that irrigates 50 m2
. A $25 drum kit employs a 200 – 300 l' drum tank for
irrigation of 125 m2
. The largest version irrigates up to 4000 m2
.
Shift-capable and simplified systems reduce capital cost by using more labor. Each
lateral can be shifted up to ten rows. In the most basic systems, water is emitted from
baffled holes or curled micro-tubes, as a substitute to emitters.

26
Larger low-cost drip systems for irrigation of 1000 to 10,000 m2
of cotton and other
field crops, cost $600-$700/ha. One lateral can irrigate four rows using attached
micro-tubes.
"Netafim International" developed two gravity-pressurized Family Drip Systems (FDS)
models for irrigating 400 m2
of vegetables.
Both types include a tank, filter, valves, main line, manifold and laterals. One model
has a 50 m long mainline and fifty 7.5 m long lateral tubes suitable for greenhouse or
low-tunnel cropping. The second model has a 9 m long main pipe and nine 20 m
long lateral tubes on both sides. The tubes are heavy-duty, durable, of small-
diameter, 5–9 mm OD. The system costs $150 per 1,000 m2
.
Complementary to these systems, a human-powered treadle pump priced at only $30
(compared to $300 for a diesel pump) was developed. There are two treadle pump
models: one is powered by walking on two bamboo treadles, while the other is
comprised of steel treadles connected to concrete platforms and tubes. The treadles
activate two steel pistons that can be manufactured in any local village blacksmith's
workshop.
Two attitudes prevail regarding simplified drip systems for a disadvantaged small-
holder. The first attitude looks for the cheapest equipment and compromises on
emission uniformity and durability, assuming that the individual farmer cannot afford
high quality products.
The other attitude advocates the reduction of system costs by elimination of
sophisticated components like automation, fertigation and high level filtration;
keeping durability and considerable uniformity of water distribution. The systems are
somewhat more expensive than in the first alternative but more cost effective in the
long run.
Fig. 5.4. Family Drip System (FDS) Courtesy "Netafim"

27
Fig. 5.5. Treadle pump (left – close-up, right – at work) Courtesy "Netafim"

28
6. PIPES AND ACCESSORIES
Pipes used in micro irrigation are made primarily of Polyethylene (PE) and
Polyvinyl Chloride (PVC).
6.1. Polyethylene Pipes
The prevalent material, Polyethylene (PE) has four material density categories:
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 g/l and above
Carbon black 2% is added to reduce the sensitivity of the pipes to ultraviolet (UV) sun
radiation.
Another classification relates to the working pressure that the pipe withstands (PN).
Common grades of PN used in irrigation are: 2.5, 4, 6, 10, 12.5 and 16 bars (atm).
Certain thin-walled laterals withstand lower PN: 0.5 – 2 bar. The pressure tolerance
depends on pipe material density and wall thickness. Tolerance data published by
the manufacturers relate to temperature of 20 C0
. At higher temperatures, the
tolerance decreases significantly, hence pipes are tested at twice the designated
working pressure and have to withstand three times the working pressure.
Plastic pipes are designated according to their external diameter, in mm. In the USA
and other countries, pipe diameter is marked in imperial inch units (“). 1” = 25.4 mm.
Pipe wall thickness is designated in mm units (in the USA by mil units. Mil = 1/1000
of inch).
1 mil = 0.0254 mm.
Laterals are commonly made of LDPE. Delivering and distributing pipes with
diameters larger than 32 mm are mostly made of HDPE.
Table 6.1. PE (polyethylene) pipes for agriculture
PE type ND (Nominal Diameter) Applications PN - m
LDPE 6 mm Hydraulic command tubing 40 – 120
LDPE 4 – 10 mm Micro-emitter 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 submains 40 – 100
HDPE 75 – 450 mm Water supply and delivery networks 60 - 160

29
Table 6.2. LDPE pipe internal (inner) diameter and wall thickness
PN
OD ↓↓↓↓
25 m 40 m 60 m 80 m 100 m
mm ID Wall
thickness
ID Wall
thickness
ID Wall
thickness
ID Wall
thickness
ID Wall
thickness
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, mostly equivalent to the ND.
ID = Internal (inner) Diameter
Table 6.3. HDPE pipe internal (inner) diameter and wall thickness
Adapted form "Plastro" brochure
6.2. PVC Pipes
PVC (PolyVinyl Chloride) is a rigid polymer. Addition of plasticizers renders flexibility
to tubes made of soft PVC. PVC pipes are sensitive to UV sun radiation. Soft and
flexible, they are used mainly in gardening and landscape. In agriculture, rigid PVC
pipes are mainly used for water delivery and distribution. PVC pipes are installed
exclusively underground to avoid damage from UV radiation. Currently, unplasticized
PVC (UPVC) pipes are manufactured with improved UV resistance and better
tolerance to pressure fluctuations. 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).
PN
OD
25 m 40 m 60 m 80 m 100 m 160 m
mm ID Wall
thickness
ID Wall
thickness
ID Wall
thickness
ID Wall
thickness
ID Wall
thickness
ID Wall
thickness
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

30
Table 6.4. 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-emitter connection to laterals 40 – 60
Soft PVC 12 – 25 mm Tapes and thin-wall drip laterals 5 – 20
Rigid UPVC ½” – 4” Risers 40 – 100
Rigid UPVC 63 – 1000 mm Supply networks, main lines, submains 40 – 240
When PVC pipes are installed in heavy or stony soil, it is recommended to pad the
trench with sand to prevent damage to the pipe wall by swelling soil and stone
pressure.
Table 6.5. Rigid PVC pipes internal diameter and wall thickness
PN 60 m 80 m 100 m
OD – mm ID – mm Wall thickness –
mm
ID – mm Wall thickness –
mm
ID – mm Wall thickness –
mm
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
6.3. Lay-flat Hoses
Flexible PVC lay-flat hoses can be used as mainlines and submains. The hose is
impregnated with anti-UV radiation protecting agents. When water shuts-down, the
hose lies flat on the ground and can be driven over by tractors and other farm
machinery. Lay-flat hoses can be positioned on the soil surface or in a shallow
trench. These hoses are available in diameters of 75 – 200 mm.
6.4. Fiberglass Pipes
In addition to UPVC and HDPE pipes, reinforced fiberglass pipes are used as a
substitution for steel and asbestos-cement pipes to deliver water under high pressure
from the water source to the irrigated area.
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.

31
6.5. 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 designated nominal
pipe diameter (ND) is its external diameter. Friction head losses of water flow in the
pipe are determined by the internal diameter.
It is imperative to check whether the designated diameter is nominal (mostly external)
or internal, when using nomograms, on-line calculators and design software.
6.6. Accessories
Accessories are classified into four categories:
a. Connectors (fittings)
b. Control, monitoring and regulation devices
c. Chemical injectors and safety devices
d. Soil moisture measuring and monitoring instrumentation.
6.6.1. Connectors (Fittings)
Connectors are made of metal or plastic materials. They may be two-sided straight-
through or angular units, T or Y shaped triple outlets, four-sided crosses or multi-
outlet splitters.
Fig, 6.1. Plastic and metal connectors

32
Connectors to control devices are threaded
or barbed. Connectors between pipes and
laterals are mostly barbed or conic. Simple
barb connectors and sophisticated
connectors with inner barb and external
locking cap are available. HDPE pipes are
jointed with locking connectors and may be
jointed on-farm by heat fusion. If properly
performed, fusion is reliable and durable.
6.6.2. Control Devices
Valves are the basic control devices.
6.6.2.1. Gate Valves are used for on-off
tasks and are unsuitable for water gradual
opening and closing or for flow regulation.
6.6.2.2. Ball Valves are used for on-off
tasks. They have low head losses but are
unsuitable for flow regulation.
Y valve Globe valve Ball valve Hydraulic valve Metering automatic
valve
Fig. 6.5. Valves
Fig.6.2. Start connectors, plugs and lateral ends Fig. 6.3. Lock fastened connectors
Fig. 6.4. Connectors and splitters

33
6.6.2.3. Globe Valves feature precise flow regulation but create relatively high head
losses.
6.6.2.4. Angular and Y Shaped Valves are suitable for flow regulation and have
lower head losses than globe valves.
6.6.2.5. Butterfly Valves have throttling capability and modest head losses.
6.6.2.6. Hydraulic Valves are manufactured in a variety of models and have a built-
in control chamber. Water pressure from the command line actuates a piston or
diaphragm that can regulate the flow by narrowing or widening the water
passageway of the valve.
Functionally, hydraulic valves fall into two categories: Normally Open (N.O.) and
Normally Closed (N.C.).
a. Normally Open (N.O.) valves stay open until the control chamber is filled with
water under system pressure. When the chamber is full, the valve shuts-off.
b. Normally Closed (N.C.) valves are kept closed by the water pressure in the
mainline. In case of a rupture in the command line, the closure is secured by
pressure of a spring. The valve is opened when a tiny valve at the top of the control
chamber opens, releasing water from the control chamber into the atmosphere.
The pressure exerted by water flowing on the lower face of the diaphragm reopens
the valve.
Normally Closed (NC) valves
create higher head losses,
but they are safer to use as
the valve remains closed
even if the command tube is
torn or plugged.
6.6.2.7. Flow Meters are
essential for accurate water
measurement. Routine bi-
annual check and calibration
are required.
6.6.2.8. Pressure Regulators are used to maintain a constant downstream pressure
independent of upstream pressure fluctuations, provided that the pressure in the inlet
is above the designated regulating pressure.
Inline ¾" Low flow 1½" × 2 2" × 4 2" × 6 3" × 10
Fig. 6.7. Pressure regulators Courtesy "Netafim"
Fig 6.6. Hydraulic valve operating principle after Y. Dvir

34
Pressure regulation is essential in
micro irrigation, particularly in drip
irrigation. Certain thin wall laterals
have a PN of 4 – 15 m, and burst
at higher pressure. When using
non-compensating drippers,
pressure regulators installed on
the manifolds or lateral inlets can
maintain uniform pressure under
harsh topographic conditions.
Mechanical devices regulate the pressure against a spring while in more
sophisticated designs pressure is controlled hydraulically by a diaphragm or piston.
The metering valve is a combination of a flow meter and hydraulic valve. The
desired volume of water to be applied is preset. The valve is opened manually or by
command from controller and closes automatically when the assigned water volume
has been delivered.
Metering valves are used extensively in micro irrigation. They facilitate gradual
opening and shutdown of the water, in order to avoid the collapse of thin-walled
laterals. They are handily compatible with automation.
Horizontal metering valve Angular metering valve Electric valve
Fig. 6.8. Control valves
The actuator in the metering valve can be a diaphragm or a piston. A diaphragm is
less sensitive to dirt in the water, but prone to tearing and collapse by pressure
surges and may wear out due to chemical degradation.
6.6.2.10. Electric Valves
Electric valves are commonly used in automation. They are actuated by a solenoid
that converts electric pulses into mechanical movement. In small diameters – up to 1”
(25 mm) – the solenoid can function as a direct actuator. In greater diameters, the
Table 6.6. Spring actuated pressure regulators
Flow rate – m3/hModel
Min. Max.
¾" Low flow rate 0.11 3.0
¾" (One spring) 0.8 5.0
1½" (2 Springs) 1.6 10.0
2"×4 (4 Springs) 3.2 20.0
2"×6 (6 Springs) 4.8 30.0
3"×10 (10 Springs) 8.0 50.0

35
solenoid commands hydraulic actuators. Energy sources are batteries, solar cells
and AC current, when applicable.
6.6.2.11. Pressure Relief Valves instantly release water under excess pressure to
protect the irrigation system. Two types of valves are available:
a. Mechanical valves, working against a spring.
b. Hydraulic devices that are more reliable but more expensive.
6.6.2.12. Air Relief Valves
Air relief valves and atmospheric vacuum breakers are essential components of
micro irrigation systems.
Air relief valves release air from the pipelines when they are filled with water and
introduce air into pipelines when they are drained on sloppy terrain. Plastic pipes,
that withstand pressure of 6, 10 bars and higher can by damaged badly when the
pressure falls below atmospheric pressure. “Double action" air relief valves release
air from the pipeline, even when the floating device is lifted by pressure buildup as
the pipeline is filled with water.
Three basic types of air relief valves are available:
6.6.2.12.1. Automatic Valve: releases small volume of air in ordinary operating
conditions.
6.6.2.12.2. Kinetic Valve: releases large volume of air while the system is filled with
water and allows a substantial volume of air to enter into the system at shutdown.
6.6.2.12.3. Combination Valves: Automatic and kinetic valves mounted together in
one assembly.
Automatic Kinetic Combination
Fig. 6.9. . Air Relief Valves

36
6.6.2.13. Atmospheric Vacuum
Breakers are small devices, ½” – 1” in
diameter that break the vacuum at water
shutdown and allow air to enter into the
system when water drains from the
irrigation system and the pipeline
pressure falls below atmospheric
pressure.
Certain types of air relief valves also
introduce air into the irrigation system
when pressure equalizes or falls below the atmospheric pressure – functioning as
vacuum breakers.
6.6.2.14. Check-Valves and Backflow Preventers
When the irrigation system is connected to a potable water supply network, check
valves and backflow preventers are used to eliminate backflow of water containing
chemicals from the irrigation system to the potable water network.
6.6.2.15. Lateral-End Flush Devices
In drip irrigation, the highest amounts of precipitates accumulate in the lateral distal
end. Automatic lateral-end flush devices release water at the start of irrigation before
the working pressure builds-up in the system. This enables automatic routine flushing
of the laterals, eliminating the need for manual flushing.
Fig. 6.10. Atmospheric vacuum breakers
Fig. 6.11. Lateral-end flushing action Fig. 6.12. Lateral-end flusher components

37
7. WATER TREATMENT AND FILTRATION
Irrigation water quality is defined by its physical, chemical and biological
characteristics. The narrow water passageways in drippers and micro-emitters are
particularly sensitive to irrigation water quality.
7.1. Physical Quality Parameters:
7.1.1 Suspended solid mineral particles
7.1.2 Organic matter
7.1.3 Live zooplankton
7.2. Chemical Quality Parameters:
7.2.1. Nutrition elements content
7.2.2. Salt content
7.2.3. The concentration of precipitate-forming ions
7.2.4. pH level
7.3. Emitter Clogging Factors
7.3.1. Particulate matter
7.3.2. Biological living organisms and their debris
7.3.3. Chemical precipitates
7.3.4. Combinations of the above mentioned factors
Poor system design and management increase dripper clogging. Preventive water
treatments against clogging are comprised of sedimentation, filtration and
complimentary chemical treatments.
7.3.1. Particulate Matter
Micro-emitters are clogged by particles of sand, limestone and other debris too large
to pass through the narrow water passageways. Clogging may also occur when small
particles stick together to form larger aggregates. Even tiny particles such as
suspended clay, which would not cause problems as discrete particles, can initiate
clogging if they flocculate to form larger aggregates.
7.3.2. Biological Substances
Emitters are clogged by particles of organic matter that block the water
passageways. Clogging may be induced by secretions of organisms such as algae
and microscopic bacteria. Certain algae are small enough to pass through filters and
emitter passageways as discrete entities, but may flocculate in pipelines to form
aggregates large enough to clog emitters. Bacteria are small and do not cause
clogging; however, they can precipitate compounds of iron, sulfur and other chemical
elements that clog the emitters. Some bacteria secrete slime that acts as an
adhesive platform for the buildup of clay, algae and other small particles into
aggregates.
Iron and sulfur bacterial slime is a widespread problem. Iron-precipitating bacteria
grow in the dissolved ferrous iron in irrigation water. These bacteria stick to the
surface of suspended soil particles and oxidize the dissolved iron. The oxidized iron

38
precipitates as insoluble ferric iron. In this process, a slime called ochre is created,
which attaches with other substances in pipelines and clogs the emitters.
Specific bacteria that oxidize hydrogen sulfide and convert it into insoluble elemental
sulfur, create sulfur slime, a white or yellow stringy deposit formed by oxidation of
hydrogen sulfide that is present mainly in shallow wells. The slime clogs emitters
either directly, or by acting as an adhesive agent for other small particles.
7.3.3. Chemical Precipitates
Chemical clogging of emitters frequently results from precipitation of one or more of
the following ions: calcium, iron, magnesium and manganese. These materials may
precipitate from the solution and form scales that partially or fully clog emitters.
Precipitation can be triggered by changes in pH, temperature, pressure and reaction
with ions that are injected into the irrigation water by fertigation as well as by
exposure to atmospheric oxygen.
Table 7.1. Relative clogging potential of drip irrigation systems by water contaminants
Water characteristic Minor Moderate Severe
Suspended solids (ppm) <50 50 -100 >100
pH <7.0 7.0-8.0 >8.0
Total dissolved solids (ppm) <500 500-2000 >2000
Manganese (ppm) <0.1 0.1-1.5 >1.5
Iron (ppm) <0.2 0.2-1.5 >1.5
Hydrogen sulfide (ppm) <0.2 0.2-2.0 >2.0
Bacteria population (per ml) <10,000 10,000-50,000 >50,000
After Blaine Hanson. 1997
7.4. Water Hardness
Water containing substantial concentrations of Ca++
, Mg++
and Fe++
is regarded as
“hard water”. Hard water is prone to the precipitation of carbonates as low-soluble
salts in the irrigation system.
Water “hardness” is expressed as a calcium carbonate concentration equivalent in
mg/l units. Hardness is calculated by measuring the content of the above mentioned
Cations, summing up their concentrations expressed in meq/l and multiplying by 50
(the equivalent weight of calcium carbonate).
The most prevalent precipitate from hard water is calcium carbonate. However when
fertigating with fertilizers that contain phosphorous and sulfur, calcium phosphate and
calcium sulfate (gypsum) may also precipitate.
Similar reactions occur with soluble magnesium bi-carbonate.
7.5. Iron and Manganese in Water
Iron is often dissolved in groundwater as ferrous bi-carbonate. When exposed to air,
the iron is oxidized, precipitates and can plug the emitters.
Manganese is occasionally present in irrigation water, but at lower concentrations
and with lower activity as a clogging factor than iron.

39
7.6. Biochemical Oxygen Demand (BOD)
Organic matter suspended in the water is decomposed by microorganisms that
consume oxygen along the process. The quantity of oxygen consumed by these
organisms in breaking down the waste is designated as the Biochemical Oxygen
Demand or BOD. BOD is a consistent indicator for dripper clogging hazard by
suspended organic matter.
Raw sewage and low-quality reclaimed water have high levels of contamination.
Water pumped from ponds, lakes, rivers, streams, canals and dam reservoirs, also
contains a high load of impurities. Water pumped from sand aquifers contains great
amounts of suspended sand.
Sand and silt separation is often performed as a pre-treatment in settling ponds and
tanks or by vortex sand separators. For circulated water in greenhouses, slow sand
filter systems are used to eliminate water-borne pathogens.
7.7. Filtration
Due to the narrow water passageways in micro-emitters and the slow water-flow
velocity, micro irrigation systems are susceptible to clogging. As mentioned before,
Clogging prevention requires high-level filtration and complimentary chemical and
physical water treatments.
Table 7.2. Characteristics of water passages in drippers (example)
Water passageway Water passagewayFlow
Rate* Length Width Depth Cross
section
Flow
rate Length Width Depth Cross
section
Non-compensated
drippers
l/h mm mm mm .mm2
Compensated
drippers
L/h mm mm mm mm2
Inline 8.0 220 1.95 1.84 2.80 PC button 8.0 13 1.39 1.45 2.00
Button 8.0 48 1.39 1.45 2.02 ” 4.0 60 1.39 1.49 2.07
Inline 4.1 258 1.35 1.45 1.95 “ 2.0 60 1.25 1.09 1.38
Button 3.8 50 1.15 1.05 1.22 Ram PC 3.5 15 1.22 1.22 1.46
Tiran 4.0 95 1.38 1.38 1.90 “ 2.3 15 1.04 1.04 1.08
Typhoon 2.8 17 0.81 0.81 0.65 “ 1.6 19 1.00 1.00 1.00
Tiran 2.0 135 1.00 1.00 1.00 “ 1.2 19 0.91 0.91 0.83
Inline 2.0 280 1.10 1.18 1.30 Midi button PC 4.0 30 1.20 1.25 1.50
Button 2.0 53 0.90 0.80 0.72 “ 2.0 32 0.98 1.00 0.98
Typhoon 1.75 20 0.71 0.71 0.5
*In non-compensated drippers – nominal flow rate at 1 bar (10 m) pressure head. Courtesy "Netafim"
7.7.1 Screen (Strainer) Filters
Screen filters are designated by filtration degree, filtration surface area and filtration
ratio.
Filtration degree is designated in microns or mesh number. The filtration degree in
microns indicates the diameter of the biggest ball-shaped particle that can pass
between the screen wires.
The mesh number counts the number of wires along a 1" length of the screen The
two concepts are not fully inter-convertible.

40
Perforation width may differ in two screens with the
same mesh number due to different wire thickness.
Conversion from one system to another is done by rule
of thumb: mesh number x microns ≈ 15,000.
When selecting the filtration degree, the dimensions of
the water passageways in the dripper and the
character of water impurities should be considered.
When the impurities are suspended inorganic solids
(sand, silt, chemical precipitates), the maximum
perforation diameter should be 25%-30% of the
narrowest dimension (width or depth) in the emitter's
water passageway. When the impurities are organic
and biological materials, the maximum perforation
diameter should not be greater than 10%-20% of the
water passageway width. Screen filters are most
suitable for water with inorganic impurities, while high
loads of organic and biological impurities may clog the
screen temporarily.
Fig. 7.2. Head losses in clean screen filters Adapted from "Odis" brochure
One of the main disadvantages of
screen filters is the rapid accumulation
of dirt on the screen's surface. The
accumulated dirt increases the head
losses and may trigger collapse of the
screen. Monitoring the pressure
difference between the filter inlet and
outlet is necessary to prevent
excessive dirt accumulation on the
screen. The filter has to be flushed
when the pressure difference between
inlet and outlet approaches 0.5 bar (5 m).
Fig. 7.1 Screen filter Courtesy
"Netafim
Table 7.3. Screen Perforation Examples
Mesh no. Hole size – microns Wire thickness -
microns
40 420 250
50 300 188
80 177 119
100 149 102
120 125 86
155 100 66
200 74 53

41
7.7.2. Disc Filters
Disc filters are suitable for filtration of water containing mixed, inorganic and organic
impurities. The casing is made of metal or plastic materials. The filtering element is
a stack of grooved rings, tightened firmly by a screw on cap or by a spring that is
compressed by a water-piston. Water is filtered as it flows from the perimeter into
the stack inner space through the grooves. The intersections of the grooves provide
in-depth filtering. Coarse particles are trapped on the external surface of the stack.
Finer particles and organic debris stick to the inner grooves. Disc filters have a
higher dirt-retention capacity than screen filters. The definition of the filtration degree
is identical to that of screen filters and can be indicated by the color of the discs.
Fig. 7.3. Disc filter
7.7.3. Media Filters
Fig. 7.4. Media filters

Micro-irrigation Technology and Applications handbook- 2009

Micro-irrigation Technology and Applications handbook- 2009

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