Planning, design and
Planning, design and
installation of
installation of
irrigation schemes —
irrigation schemes —
Part 5: Guide for irrigation equipment
Part 5: Guide for irrigation equipment
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-This British Standard, having This British Standard, having been prepared under the been prepared under the direction of the Agricultural direction of the Agricultural Machinery and Implements Machinery and Implements Standards Policy
Standards Policy
Committee, was published Committee, was published under the authority of the under the authority of the Standards Board and Standards Board and comes into effect on comes into effect on 15 November 1993 15 November 1993 © BSI 07-1999 © BSI 07-1999
The following BSI references The following BSI references relate to the work on this relate to the work on this standard:
standard:
Committee reference AGE/30 Committee reference AGE/30 Draft for comment 88/72250 DC Draft for comment 88/72250 DC
ISBN 0 580 22447 3 ISBN 0 580 22447 3
The preparation of this British Standard was entrusted by the Agricultural The preparation of this British Standard was entrusted by the Agricultural Machinery and Implements Standards Policy Committee (AGE/-) to Technical Machinery and Implements Standards Policy Committee (AGE/-) to Technical Committee AGE/30, upon which the following bodies were represented:
Committee AGE/30, upon which the following bodies were represented: Agricultural Engineers’ Association
Agricultural Engineers’ Association
British Agricultural and Garden Machinery
British Agricultural and Garden Machinery Association Ltd.Association Ltd. Health and Safety Executive
Health and Safety Executive
Ministry of Agriculture, Fisheries and Food Ministry of Agriculture, Fisheries and Food National Farmers’ Union
National Farmers’ Union Silsoe College
Silsoe College
Silsoe Research institute Silsoe Research institute UK Irrigation Association UK Irrigation Association National Rivers Authority National Rivers Authority Well Drillers’ Association Well Drillers’ Association
Amendments issued since publication Amendments issued since publication Amd. No.
Amd. No. DateDate CommentsComments
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-This British Standard, having This British Standard, having been prepared under the been prepared under the direction of the Agricultural direction of the Agricultural Machinery and Implements Machinery and Implements Standards Policy
Standards Policy
Committee, was published Committee, was published under the authority of the under the authority of the Standards Board and Standards Board and comes into effect on comes into effect on 15 November 1993 15 November 1993 © BSI 07-1999 © BSI 07-1999
The following BSI references The following BSI references relate to the work on this relate to the work on this standard:
standard:
Committee reference AGE/30 Committee reference AGE/30 Draft for comment 88/72250 DC Draft for comment 88/72250 DC
ISBN 0 580 22447 3 ISBN 0 580 22447 3
The preparation of this British Standard was entrusted by the Agricultural The preparation of this British Standard was entrusted by the Agricultural Machinery and Implements Standards Policy Committee (AGE/-) to Technical Machinery and Implements Standards Policy Committee (AGE/-) to Technical Committee AGE/30, upon which the following bodies were represented:
Committee AGE/30, upon which the following bodies were represented: Agricultural Engineers’ Association
Agricultural Engineers’ Association
British Agricultural and Garden Machinery
British Agricultural and Garden Machinery Association Ltd.Association Ltd. Health and Safety Executive
Health and Safety Executive
Ministry of Agriculture, Fisheries and Food Ministry of Agriculture, Fisheries and Food National Farmers’ Union
National Farmers’ Union Silsoe College
Silsoe College
Silsoe Research institute Silsoe Research institute UK Irrigation Association UK Irrigation Association National Rivers Authority National Rivers Authority Well Drillers’ Association Well Drillers’ Association
Amendments issued since publication Amendments issued since publication Amd. No.
Amd. No. DateDate CommentsComments
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-This Part of BS 7562 has been prepared under the direction of the Agricultural Machinery and Implements Standards Policy Committee and contains
recommendations on good practice in the planning, design and installation of irrigation schemes in the UK, together with information and guidance. It is intended for the use of engineers and farmers having some knowledge of the subject. It embodies the experience of engineers successfully engaged on the design and construction of irrigation schemes so that other reasonably qualified engineers may use it as a basis for the design of similar irrigation schemes. This Part of BS 7562 contains information and represents good practice at the time it was written and, inevitably, technical developments may render parts of it obsolescent in time. It is the responsibility of engineers concerned with the design and construction of schemes to remain conversant with developments which have taken place since publication.
This standard has been prepared in six Parts as follows. — Part 1: Glossary of terms;
— Part 2: Guide for acquisition of site data; — Part 3: Irrigation water requirements1); — Part 4: Guide to water resources;
— Part 5: Guide for irrigation equipment;
— Part 6: Guide for feasibility and implementation procedures.
A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations.
Summary of pages
This document comprises a front cover, an inside front cover, pages i an d ii, pages 1 to 26, an inside back cover and a back cover.
This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.
1 Scope
This Part of BS 7562 gives guidance on the
equipment required for irrigation schemes. It deals specifically with sprinkler and trickle/bubbler irrigation as the most common methods of irrigation in the UK and covers in-field irrigation equipment, pipelines, pump installations, and pump suction and delivery pipework.
2 Informative references
This Part of BS 7562 refers to other publications that provide information or guidance. Editions of these publications current at the time of issue of this standard are listed on the inside back cover, but reference should be made to the latest editions.
3 Definitions
For the purposes of this Part of BS 7562 the definitions given in BS 7562-1:1992 apply.
4 Sprinkle in-field equipment
4.1 Introduction
This is the equipment which is laid out, temporarily or permanently, in the field being irrigated. A wide range of in-field equipment is available but that commonly used in the UK is described in this British Standard. A classification is provided in Table 1.
The selection of appropriate in-field irrigation equipment is based on many factors including capital cost, operating cost, labour requirements and suitability for the farm.
4.2 Water application devices 4.2.1 General
The function of water application devices is to apply water as uniformly as possible to the crop and soil. The most common application devices used to apply water are rotary impact sprinklers, guns and fixed spray heads.
4.2.2 Rotary impact sprinklers
Rotary impact sprinklers are the devices most in use for spraying water.
Sprinklers of varying sizes may be used on a wide range of irrigation systems including conventional and mobile lateral systems, see Table 1.
The design and performance requirements for rotary impact sprinklers are described in BS 7459-1 and BS 7459-2.
Sprinklers should be operated within the
manufacturers’ specified range of pressures for uniform water application. Sprinkler operation with too high a pressure will cause excessive break up of the water jet, loss of wetted radius and excess water applied near the sprinkler head. Low operating pressure at the sprinkler will result in inadequate break up of the jet, large droplets and uneven application of water.
The size of the nozzle(s) determines the sprinkler discharge and the wetted diameter. Nozzle
diameters range from 2 mm to 3 mm up to 50 mm. Sprinklers may have one or two nozzles.
Common trajectory angles for sprinklers are 24°
and 30° measured from the horizontal. Such sprinklers are used on a wide variety of irrigation systems, including hand move and mechanical move equipment. Low angle sprinklers, having trajectory angles ranging from 0° up to about 15° produce a profile which is less subject to distortion by wind but may not be as uniform in application. Typical applications for low angle sprinklers include under tree orchard irrigation and centre pivots operating in windy conditions.
The average application rate from the sprinklers (in millimetres per hour) should not exceed the basic infiltration rate (in millimetres per hour) of the soil. This ensures that water infiltrates into the soil thus avoiding the problem of surface water run-off. The uniformity of water application is described by Christiansen’s coefficient of uniformity. Details of the coefficient and its measurement are provided in BS 7459-2. The choice of the most appropriate uniformity coefficient depends largely on the crop being irrigated.
The spacing between sprinklers should be as recommended by the manufacturer and shown in performance tables. The wetted patterns from sprinklers should overlap to achieve an appropriate coefficient of uniformity. The degree of overlap will vary according to the water application pattern and the wind conditions.
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-Table 1 — A classification of sprinkle irrigation systems used in the UK
Wind will distort the wetting patterns of sprinklers. The amount of distortion depends upon the wind speed and the size of the water droplets. The greater the wind speed and the smaller the water droplets the more distortion will occur. Wind distortion can be counteracted by spacing the sprinklers closer together but care should be taken as this may also increase the application rate. If the application rate exceeds the infiltration rate of the soil, run-off may occur. The direction of the wind may be an
additional problem especially if the wind direction changes during the irrigation set. In this situation the best results may be obtained by ignoring the effects of wind altogether and operating the
sprinklers on their recommended spacings for low wind speeds.
4.2.3 Guns
Guns are large rotary sprinklers which have a large wetted diameter. They are commonly used in mobile systems in the UK but they can also be used in conventional systems.
Guns may be used on various irrigation systems either fixed or mobile. They normally have
discharges from 10 m3/h up to and above 125 m3/h and operate at pressures from 2.0 bar2) up to and above 8.0 bar. The selection of the operating pressure depends upon nozzle size and type and droplet size required.
Water droplet sizes from guns may be unacceptably large for certain soil types and crops, causing
damage to both soil and crop. Careful selection of nozzle diameter and type and operating pressure should be made to ensure that the resultant droplets are suitable for the soil and the crop.
Gun nozzle diameters can vary from 12 mm up to and above 40 mm.
Two main types of nozzle are available; ring nozzles and taper nozzles. Ring nozzles are designed to produce acceptable droplet sizes at lower operating pressures. Taper nozzles are designed to produce the maximum wetted throw but droplet sizes are increased.
The throw is not only affected by the operating pressure and nozzle diameter and type but also by the construction of the gun. The length of the range tube and its diameter, plus the use of straightening vanes inside the range tube, combine to affect the maximum throw.
The application rate tends to be greater than for the small rotary impact sprinklers. The recommended spacing depends upon the wetted diameter, wind speed and direction and the required coefficient of uniformity. Gun spacing recommendations vary according to whether the gun is working on a grid system, a mobile unit or is used on a centre pivot or linear move.
Systems Water application devices
Conventional systems — portable — hand move — roll move — tow line
Mainly use small rotary impact sprinkers, but guns, fixed sprays and bubblers are also used
— semi-permanent — sprinkler hop — pipe grid — hose pull — permanent
Mobile gun systems — hose drag — hose pull
Mainly guns, but in some cases the gun is replaced with a boom device with small rotary impact sprinklers or fixed sprays
Mobile lateral systems — centre pivot — linear move
Small rotary impact sprinklers or fixed sprays Spray lines — stationary — oscillating — rotating Fixed sprays 2)1 bar = 105 N/m2 = 105 Pa.
Guns may be used for full or part circle irrigation. Full circle irrigation would usually be applicable to fixed grid irrigation systems. Mobile gun systems usually use part circle applications of 270° to 300°
arc. Guns may also be used on the end of centre pivots and linear move machines to irrigate an arc of 180° or less.
There are two main types of drive systems used for rotating the gun. Impact drives operate using the water flow that leaves the nozzle moving an impact arm up and down or sideways causing the gun to rotate. Gear drives operate by passing a small quantity of the main supply through or over a turbine gear drive assembly. This causes the gun itself to rotate via a gear mechanism.
The drive mechanism may be affected by water quality. Care should be taken with gear drive systems to ensure that grit or other particles do not cause the drive system to fail. Filtration equipment may be required for some systems.
Guns normally operate with trajectory angles between 18° and 25°. Low angle guns may be used on applications where wind affects the gun
performance, but the wetted diameter of the gun is reduced. Adjustable trajectory guns may be suitable for certain situations such as operating in high wind conditions where reduced wind drift is required. The part circle mechanism fitted to guns should provide adequate adjustment to cover the range of arcs required. Usually the range is between 45°
and 330°. When returning to the start position, the reverse action of impact driven guns may occur at high speed. In this case the riser assembly should be strong enough to resist the forces. Operator safety should be considered where there is a risk that a gun may hit the operator when fast reversing. Slow reverse action sectoring devices are often now used on guns and these produce less strain on the
connection assemblies.
The thrust forces resulting from gun operation may be high due to the flows and pressures used and the construction of the riser is critical for correct gun performance. The riser strength should be sufficient with its support to prevent flexing of the riser which may cause either failure or poor gun performance. Risers used on grid systems should be designed with adequate support structures to ensure that when the gun is operating the riser is sufficiently stable. The riser should be of suitable diameter to ensure that the velocity of water through it is not excessive causing high turbulence which may affect the performance from the gun. Risers fitted to the trolley units used on self travellers should be sufficiently strong to resist breakage. The trolley base should be so designed that there is no risk of tipping over when operating under normal
irrigation conditions. 4.2.4 Fixed spray heads
Fixed spray heads may be used to apply water either to the total ground area or to a specific area around a plant.
Spray jets may be used on conventional irrigation systems, such as under tree irrigation and also on centre pivots and linear move machines.
4.3 Sprinkle irrigation systems
NOTE The irrigation systems most commonly used in the UK are listed and classified in Table 1.
4.3.1 Conventional systems 4.3.1.1 General
Conventional systems are the most common type of system in use and comprise pipes, small rotary impact sprinklers and risers which are moved, often by hand, around the field to complete an irrigation. A characteristic of this type of system is that the
pipes and sprinklers are stationary during irrigation and then moved between irrigations.
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-4.3.1.2 Portable
The most basic and simplest system is the portable hand-move system. The pipes and sprinklers are all portable and moved by hand for each irrigation. As this tends to be very labour intensive, several developments have been made to this system to reduce the labour input.
If the field layout allows, the laterals which carry the sprinklers should be laid along the contours to ensure as little pressure variation as possible caused by difference in height. The lateral may be operated down the slope provided that the
maximum pressure variation along the lateral does not exceed 20 % of the sprinkler’s recommended operating pressure. If the slope would cause a greater pressure variation, then pressure regulators should be fitted to the sprinklers to produce correct operation. A pressure regulator may be fitted under the sprinkler inlet connection or a pressure
regulating/flow controlling nozzle may be inserted at the nozzle. Sprinkler laterals may be laid out up the slope where this is the only possible layout. Pressure regulating or flow regulating devices should be fitted to the sprinkler where the pressure variation along the lateral is greater than 20 % of the sprinkler’s recommended operating pressure. Ideally, sprinkler laterals should be laid out at right angles to the prevailing wind for a more u niform irrigation. This should take preference over layout in relation to contours.
The number of irrigation sets per day depends on the depth of water to be applied at the rate per hour and the time it takes to move the sprinkler laterals. The fewer the number of irrigation sets per day and the longer the number of hours per set the greater will be the total possible operating hours per day. The application rate (in millimetres per hour) relates to the application heads applying water on a unit area operating on a grid system, either square, rectangular or triangular The application rate per hour calculated here is used to estimate the total depth applied during the irrigation set.
Several factors affect the sprinkler spacing, both along the lateral and between laterals. These include wind speed, coefficient of uniformity, application rate, the crop and the soil. Sprinkler spacing should be reduced according to wind speed. The lateral pipe diameter is chosen so that the pressure loss along the lateral is less than 20 % of the recommended operating pressure of the
sprinkler. In this way the changes in pressure will not seriously affect sprinkler performance and uniformity.
Normally sprinkler laterals should not
exceed 100 mm in diameter as bigger pipes are much heavier and are more difficult to move around the field.
Pipe lengths usually used for sprinkler laterals are either 6 m or 9 m. Pipes that are 6 m are lighter in weight, are easier to connect and disconnect and are preferred, especially if large diameter laterals a re used.
Sprinkler risers should be of sufficient height to allow the sprinkler to irrigate over the top of the crop and should be adequately supported to avoid bending and vibration as the sprinkler rotates. Both aluminium and steel lightweight galvanized steel pipes may be subject to corrosion if fertilizers or other chemicals are applied through the
irrigation system. The manufacturer of the pipe and fittings should be consulted if this practice is
considered.
The ease of connection and disconnection of coupling lateral pipes should be considered carefully when selecting the type to be used. Couplings that can be operated by one person may be favoured where labour is short.
Sprinkler risers may have either permanent or quick coupling connections to the sprinkler lateral. The type of riser used depends upon the method of operation of the system, the riser height and the stability required.
The following briefly describes types of portable hand-move systems.
a) Roll-move system
The roll-move system comprises a sprinkler lateral mounted on wheel assemblies so that the lateral forms the axle for the wheels. The
sprinkler lateral is stationary while irrigating. The water supply to the lateral is closed off when it is moved. A power unit provides the power source for driving the wheels.
It is preferable that the system is operated in level fields to alleviate potential problems that may be caused by uneven ground. If used on sloping ground, the system should be aligned with the lateral at right angles to the land
contours. If it is operated running parallel to the contours there is a risk that the unit may run down the slope while the system is operating. Brake equipment may be fitted to the wheel assembly to prevent this happening.
A balance weight self-levelling device is included in the connection for each of the sprinklers to ensure that the sprinkler operates in the vertical position when irrigating.
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-b) Towline system
The towline irrigation system uses equipment similar to that used for the conventional hand move portable system. The lateral pipe is mounted on wheeled bases so that it can be towed from one irrigation set position to another. Special fittings are required for the base of the sprinkler pipe and also to support the pipe couplings.
Usual diameters on towline sprinkler laterals are 75 mm and 100 mm. Larger diameter pipe may be heavy to pull and therefore more difficult to move. Smaller diameter pipe may not have the strength suitable for the pulling operation.
4.3.1.3 Permanent systems
When sufficient laterals and sprinklers are provided to cover the whole irrigated area so that no
equipment needs to be moved during the irrigation season the system is called a solid-set system. The pipes are laid out at the beginning of the season and collected at the end.
When the pipes and sprinklers are left in place from season to season the same system is generally referred to as permanent. It is usually used on permanent crops such as orchards.
4.3.1.4 Semi-permanent systems 4.3.1.4.1 General
This range of systems has some equipment which is permanently fixed whilst other equipment is moved around the field. Generally this increases the capital cost of the system but greatly reduces the labour required for operations.
4.3.1.4.2 Hop systems
A hop system combines the basic characteristics of the portable hand move system with the ability to move the sprinklers to alternative positions along the lateral. This reduces the number of times that the laterals are moved.
It may be possible to operate for a greater number of hours per day using this system.
The application rate is calculated for a single
sprinkler head application as there is no immediate overlap between the sprinklers. Application rates are therefore suitable for a wide range of soils and crops.
4.3.1.4.3 Pipe grid systems
A pipe grid system consists of a complete field layout of pipes, made of either aluminium or lightweight galvanized steel. The pipes, usually 25 mm
diameter, are normally laid down at the beginning of the season. Only the sprinklers are moved to complete the irrigation cycles.
4.3.1.4.4 Hose-pull system
A hose-pull system comprises a sprinkler complete with a stand and support assembly connected to the lateral by a flexible hose. The assembly can operate in several different positions from one connection point working on a grid layout.
4.3.2 Mobile gun systems 4.3.2.1 General
Mobile systems are distinct from conventional systems because they are moving when applying irrigation water rather than being stationary. This usually improves application uniformity. It also greatly reduces the labour required for irrigation. Mobile gun systems use a large single gun type sprinkler to apply water.
4.3.2.2 Hose-pull system
This system uses a hard hose which is wound onto a large diameter drum and a gun sprinkler mounted on a trolley. The equipment is operated by towing out the gun and trolley to the furthest position for irrigation in the field. The system is started up and as the gun and trolley irrigate, the hose drum rotates slowly to wind in the hose and the gun. For subsequent set positions the hose drum may simply be rotated or may be moved to another hydrant point position.
4.3.2.3 Hose-drag system
The hose-drag system comprises a gun mounted on a chassis with a cable drum winding mechanism, a length of winding in cable and anchor and a length of flexible lay-flat hose. The irrigation system operates by positioning the chassis, complete with gun, at the end of the field. The tow cable is pulled out to the other end of the field and anchored. The flexible hose is connected to the chassis and to the water supply valve point. As the gun irrigates, the cable drum gradually winds in, pulling itself along the cable and at the same time dragging the lay-flat hose behind it. If a central water supply valve is used for the supply of water, the irrigation unit can cover twice the area as it is able to irrigate both sides of the valve point. For example, if the machine uses 200 m of hose then it is possible to cover a 400 m wetted strip per irrigation set.
4.3.3 Mobile lateral systems 4.3.3.1 General
Many new irrigation systems have been developed in recent years to try and combine the advantages of conventional sprinkler systems with the mobility of rainguns. These are called mobile lateral systems because they use laterals which move continuously while irrigating. - ` ` , , ` ` ` , , , ` ` , ` ` ` , ` ` , ` ` ` ` ` ` , ` ` , - ` - ` , , ` , , ` , ` , , `
-4.3.3.2 Centre pivot systems
This comprises a lateral pipe supported by a series of towers on wheel drive assemblies. The lateral rotates slowly around a central point irrigating a circular area.
Centre pivots can usually irrigate large areas up to 100 ha with one machine and can be highly automated.
The maximum length of lateral depends on the construction features of the centre pivot and the configuration of the pipe spans. Pivots with 125 mm diameters usually have a limitation of up to 400 m length.
Although normally the most economic centre pivot unit is one that rotates in a circle it is also possible to irrigate part circles and to have corner systems and end gun units connected and to the centre pivot. End guns add additional capacity to the machine so that it can irrigate into corners of rectangular fields and awkward field shapes.
Due to normally high coefficient of uniformity from a centre pivot irrigation system, it may be
practicable to apply chemicals and fertilizers through the irrigation system.
Application head accessories include drop arms, drop pipes and booms. Drop arms may be used in conjunction with spray nozzles to allow the water to be applied near the soil surface and to the top of the crop. The effects of windrift and evaporation may be reduced by this procedure.
Booms may be connected to the centre pivot pipe spans to enable water to be applied at low pressure as a fine even spray pattern using spray heads. The use of a boom allows the application of water over a wider area and should reduce the instantaneous application rate and improve the infiltration rate into the soil.
4.3.3.3 Linear-move system
The linear move irrigation system comprises
irrigation equipment which is designed to irrigate a square or rectangular area whilst moving slowly across the field. System components are similar in construction to the centre pivot using tower spans, and lateral pipes connected to the tower spans. Water is either fed to the centre of the machine or supplied to one end, being taken from either an open ditch or canal or from water supply points or
hydrants on a pressurized main. A central power unit, which may comprise a pump unit on an open water supply system, uses a generator unit to provide the electrical power for operating the linear move.
4.3.4 Spraylines 4.3.4.1 General
Sprayline irrigation equipment uses fixed spray heads and may be fixed upon supports above ground level. It can either be static, oscillate from side to side or rotate while irrigating.
4.3.4.2 Fixed/oscillating system
The area irrigated by sprayline equipment is usually small in comparison with other types of irrigation system.
Small diameter fixed spray nozzles are installed on the lateral and so it may be necessary to use a filter at the water source to avoid blockage.
Spraylines apply water at low application rates. Variation of application rate can only be achieved by
using different size nozzles or a change of pressure, but the range of nozzle sizes is limited.
The sprayline operates at relatively low pressure and therefore pressure regulating or pressure compensating facilities are not normally used. Thus fields should be as level as possible along the run of the sprayline lateral pipe to avoid excessive
pressure variation.
Sprayline equipment usually uses piping with a diameter of either 25 mm, 32 mm or 50 mm. Due to the small diameter of the sprayline, flow rates that can be achieved per sprayline are relatively low. The sprayline is usually supported above the crop either on short or tall trestles or spikes.
Wind may adversely affect performance due to the small spray droplets discharged from the nozzles. To counteract some of the effects of wind on the spray it may be possible to offset the nozzles and/or the oscillating mechanism so that better irrigation is achieved.
The irrigated area per set depends upon the length of the sprayline lateral and the width between the subsequent sprayline operating positions. A typical area of 0.1 ha per irrigation set is approximately the maximum possible from this type of irrigation equipment per sprayline lateral.
4.3.4.3 Rotating spraylines
A rotating sprayline comprises an irrigator unit fitted with booms which rotate by the water
pressure from the jets fitted to the booms. The unit is stationary during irrigation. At the end of the set the system is closed down and the unit moved to its subsequent position. -` ` , , ` ` ` , , , ` ` , ` ` ` , ` ` , ` ` ` ` ` ` , ` ` , -` -` , , ` , , ` , ` , , `
-5 Trickle/bubbler in-field equipment
5.1 Introduction
Trickle/bubbler irrigation uses emitters or bubblers to apply water locally to individual plants. The systems operate at low pressure and equipment is usually laid out over the complete area to be irrigated and may irrigate either the complete ground area or a percentage of the total ground area depending on the location of emitters. Trickle irrigation is sometimes referred to as drip irrigation.
5.2 Water application devices 5.2.1 Emitters
The function of emitters (sometimes called drippers) is to apply water to the roots of the plant. They are described in detail in ISO 9260.
The operating flow range for an emitter is usually 2 l/h to 12 l/h. The discharge selected
depends upon the crop irrigation requirements, the plant spacing and the soil type.
The usual range of emitter operating pressure is between 0.5 bar to 1 bar. Some devices operate over a wider range, up to 2 bar, especially those devices which are pressure compensating.
The sensitivity of emitters to clogging plays an important part in their correct performance. The manufacturer should recommend the maximum particle size filtration requirement for emitters to operate correctly. The susceptibility of emitters to clogging from chemical deposits and algae growth should be considered carefully to ensure that the correct type of device is selected. Emitters may have a built-in filter system which is able to remove some suspended material from the water flow. Self
flushing emitters also have the ability to flush particles with the irrigation water.
Not all of the root zone of the crop needs to be wetted with trickle irrigation. The percentage of wetted area irrigated depends upon the type of crop. For wide-spaced crops, wetting may only need to cover 33 % to 50 % of the soil area, while close grown crops may require 100 % wetting of the ground area.
Note that this does not mean that only 33 % to 50 % of the water needs to be applied. The crop still requires the same amount of water irrespective of the application method.
Laminar flow emitters (that is micro tubes, capillary tubes and spiral path emitters) are simple, reliable and inexpensive but need proper system design and operation to perform well. They are relatively pressure sensitive and are susceptible to clogging because of their low velocity flow, small path
diameters and varying flow rate with temperature.
Turbulent flow emitters (sometimes called drip tapes) regulate water flow by dissipating energy in friction against the walls of the water passage. They are less susceptible to clogging and pressure
variations and unaffected by changes of water temperature within normal operating limits. Vortex emitters are less pressure sensitive than
turbulent flow emitters. They are generally more susceptible to clogging by soil particles or other contaminants due to their very small water passages and need higher quality filtration and efficient management of maintenance procedures. Pressure compensating emitters (either laminar or turbulent flow devices) utilize the inlet pressure to modify the flow path size, shape or length. The pressure compensating devices are able to deliver the design flow rate over a wider range of inlet pressures. The elastomeric material used in the emitter may change its property as it ages. If the trickler is used over undulating ground where there is a variation in height along the laterals then pressure compensating emitters should be used. Self-flushing emitters may often be pressure compensating as well. At low pressures, up to about 0.5 bar, the emitter will flush, and at about 0.8 bar to 1 bar the emitter operates in the correct drip mode. The pump capacity and irrigation system design should be such that the system will operate correctly when the emitters are flushing. Emitters automatically self-flush, they may also be manually flushed.
Trickle irrigation systems may be installed above or below ground. On above ground installations the emission devices can be checked and visually seen to be operating, but may be damaged by either persons or animals. Growth of algae at the outlet of the emitters may occur but this depends on the design of the emission device.
Trickle irrigation laterals may be installed
underground using mole ploughing techniques or by individual narrow trenching. Tubing may be
connected to the emitters to bring the water from the emitter up to ground level or water may pass directly from the emitter into the soil to the root zone of the crop.
5.2.2 Bubblers
Bubblers are used to apply water either as a small stream of water or as a spray to a localized area around individual plants.
Typical flow rates for bubblers range from 1 l/m to 10 l/m for solid-set bubblers. Flow rates for bubblers used on mobile irrigation systems range from 1 l/m to 80 l/m. It is possible to adjust the flow rate from some bubblers by operating the screwed adjusters fitted to them.
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-Bubblers are designed to operate over a range of pressures from 0.1 bar to 1.5 bar. Bubblers fitted with pressure regulators, or of special design, may operate at higher pressures than those stated. The range of pressure regulations available for bubblers fitted with pressure regulators varies
between 1.5 bar and 6 bar.
Bubblers are generally used on solid-set or
permanent systems, however they can be used on mobile irrigation machines such as centre pivots or linear moves.
5.3 Trickle systems 5.3.1 General
Trickle systems are usually laid out permanently with the crop and comprise a control head unit and a layout of pipes fitted with emitters. Bubbler systems are laid out in a similar manner. 5.3.2 Control head
This control is at the head of the irrigation system and comprises filtration, pressure, and discharge controlled fertilizer injection. Control may be by either manual or automatic valves. Manual systems usually incorporate a control valve which is opened and closed as required, by an operator, to meet the irrigation requirements. Automatic control valves may operate on a time clock, on a volumetric control valve or may be linked to operate by relating to a sensing system within the soil/crop environment. The type of filter and filtering capacity of the filter will depend upon the equipment being used and the water quality. Main filtration should be completed at the pump station. Secondary filtration should be installed at the control head, to help in ensuring that water passing to the drip laterals is free from particles causing potential blockage.
Pressure regulation equipment may be required to ensure that the laterals operate at the correct pressure. Pressure regulation equipment should prevent overpressurization and potential damage to the laterals.
As there is usually good uniformity of application and potentially efficient use of the water both fertilizers and other chemicals may be applied in the water. Filtration equipment should always be installed after the fertilizer or chemical injection point into the system to ensure that chemical particles do not pass through into the system.
5.3.3 Lateral layout
The variation of temperature between daytime and night-time may cause the lateral tubing to expand and contract. To reduce the effects of expansion and contraction, tubing should be arranged in a
snake-like form. This should ensure that
emitters/bubblers stay at the location where they should be operating. Under UK climatic conditions, the variation between day and night temperatures might cause an expected expansion/contraction of the tubing up to 0.1 m per 30 m of tubing. Therefore a small amount of snaking of the tube should be sufficient.
Laterals may be installed below ground level preferably deeper than 300 mm. This should eliminate expansion/contraction in the pipe and prevent the effects of sunlight damaging the tubing. Laterals should extend 1.5 m to 3 m beyond the last emitter/bubbler point on the lateral to collect any deposits which may have passed through into the system. This practice should help to prevent blockage.
An allowance of 3 % extra in length for laterals should be normal practice to ensure that they are of sufficient length to irrigate the required area. 5.3.4 Emitters
The number of emitters or bubblers on a lateral will depend upon the emitter or bubbler discharge, their spacing, the diameter of the lateral and the
permissible pressure and flow variation within the lateral. The maximum pressure variation and its effect on flow will depend upon the type of emitter or bubbler device being used. If pressure compensating devices are used it may be possible to have a greater variation of pressure between the inlet and the end of the lateral. Normally, the variation in emitter discharge along a lateral should not be greater than±10 % of the nominal flow.
The system discharge is determined by the
maximum number of emitters/bubblers operating at any given time to satisfy the crop water
requirements.
Management of trickle/bubbler systems should be a simple routine as the labour requirement for
operating the system is low. Normally only opening and closing of control valves is required with routine checking.
Water quality for trickle/bubbler irrigation is dealt with in Part 33) of this British Standard. The filtration requirements of the water are critical chemically, physically and bacteriologically.
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-The potential efficiency of trickle/bubbler irrigation systems is approximately 90 %, with a correctly designed, installed and operated system. However, in practice it may be well below this figure if the system is not managed properly. Water losses may occur through the soil if excessive amounts of water are applied above the crop water requirements. However, as water need only be applied to the root zone area of the crop instead of the total soil area there is a potential here for saving water by reducing losses.
Due to the low labour requirement it may be
possible to operate the maximum number of h ours per day and night especially if the control valves are fully automated. The system is not affected by the climate in the same way as spray, sprinkler and gun systems.
6 Pipes and fittings
6.1 Introduction
The most commonly used pipe materials in UK irrigation systems are polyvinyl chloride (PVC) pipe for underground mains and aluminium pipe for above ground mains.
Other pipe materials, not so commonly used, include polyethylene pipes and asbestos cement pipes for underground mains; steel and cast iron pipes for specials; and lightweight galvanized steel pipes and polyethelene pipes for above ground mains.
6.2 General considerations 6.2.1 Introduction
This clause contains recommendations on the installation of pipelines and deals with those aspects of aquisition, rights of way, construction, operation and maintenance which affect land and which are common to all applications and materials. 6.2.2 Routeing
The choice of pipe route should be based on the equipment design and layout and the most economical route to achieve these requirements. Factors affecting routeing may include existing underground services, potential development areas, aquifers, ancient monuments, nature reserves, Areas of Outstanding Natural Beauty or Site of
Special Scientific interest, trees, minerals, risk of subsidence and highly productive land.
6.2.3 Land and rights of way
The route may pass through land belonging to other people, and may cross roads, streams, railways, etc. For all these considerations it will be necessary to contact the other parties who may be involved.
6.2.4 Plans
Plans are necessary for all installations where pipelines are to be installed underground, so that a record can be available for future reference. Plans to suitable scales should be produced to provide an accurate record.
6.3 Pipe laying and reinstatement
Before work starts, a record should be made of the state of the land and particular notes made of any special features so that they may be adequately reinstated if disturbed. This record should be agreed with the occupier and, wherever possible, the owner. An adequate working width should be arranged so
that the construction equipment can operate
satisfactorily. Temporary bridging and widening of access roads for the passage of plant and equipment may be required. Temporary fencing, access bridges and roads should be to a standard as agreed. Due attention should be paid to felled trees, top soil removal and temporary fencing.
For buried pipelines, the trench width and depth should be suitable for the correct installation of the pipeline. Both the width and depth may vary
according to the pipe being installed and the method used.
Existing services, such as water and gas pipes, cables, cable ducts and drains, should be accurately located and the irrigation pipeline installed taking care not to affect the other services.
Ditches may be crossed under or over depending on the site.
Special methods of construction may be required when pipelines cross canals, roads and railways. Where pipelines cross or pass along a highway the exact siting and constructional details should be agreed with the highways authority.
Backfilling operations should follow as closely as possible to the laying of the pipe, be well compacted and be reinstated in the proper sequence.
The selection and application of valves required for pipelines will depend upon the design and
specification. Reference should be made to clause 8 of this Part of this British Standard.
Provision should be made at every bend, branch and dead end in a main to resist the hydraulic thrust. 6.4 Design considerations
6.4.1 Friction loss
Friction losses in pipework and fittings may be a significant part of the pressure required to operate an irrigation system. It is therefore essential that the design of the pipework and fittings is completed for correct overall system performance.
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-Friction losses for different pipe materials should be available from manufacturers.
6.4.2 Waterhammer and surge
Both waterhammer and surge can cause problems in irrigation systems especially failure of pipelines. Waterhammer is a pressure wave which can occur when water flowing in a pipeline is s uddenly stopped, for example when a valve is closed. The intensity of the waterhammer can be severe and depends upon the valve closing time, the water velocity and the length of the pipeline involved. Surge in pipelines is the mass movement of water, often as a result of waterhammer, and can occur, for example, when a pump suddenly stops as a result of power failure.
If the irrigation system is designed and operated with velocities of less than 1.5 m/s in the pipeline, the risk of waterhammer and surge is reduced, although not eliminated.
The total pressure in pipelines includes the operating pressure of the pipeline and the additional pressure caused by potential waterhammer or surge.
Waterhammer and surge may be reduced by one or more of the following methods.
Reducing the effective length of the pipeline by the incorporation of more valves of a suitable specification in the line.
Reducing the velocity.
Increasing the closing time of the valve.
Installing suitable pressure regulating valves. Installing suitable air valves.
6.4.3 Thrust blocks
Pipelines operating under pressure can be subject to movement caused by thrust forces, at any change in direction or termination. External anchorage should be provided, usually in the form of concrete thrust blocks, to resist the thrust forces.
External anchorage should be provided at all changes in direction and at points where
termination of water flow may occur Thrust blocks are therefore recommended at all tees, end caps, bends, valves, etc.
6.5 Plastics pipework (thermoplastic material) 6.5.1 General principles and choice of
materials
Materials considered here include unplasticized PVC pipe (for cold water services), low density polyethylene and high density polyethylene pipe.
Plastics pipes have good hydraulic characteristics resulting in low frictional losses and high flow capacities. They will not corrode in contact with water ensuring that their good hydraulic
characteristics are maintained throughout their life.
The coefficients of expansion of plastics materials are generally much greater than those of metals and particular care should be taken in the design of pipework layouts above ground.
Plastics are resistant to many chemicals and are thus suitable for installation in aggressive soils. Some of the materials are degraded by exposure to direct sunlight unless their composition includes additives to resist the effects of sunlight.
6.5.2 installing buried pipes
Pipe with diameters up to 150 mm can be jointed on the surface and subsequently arranged in a
snake-like form in the trench, this eliminates the need for wide trenches. Plastics pipes may also be mole-ploughed into the ground.
Good trenching practices should be followed to achieve correct installation of the pipe, including bedding, side filling and backfilling.
6.5.3 Testing
After installation it is essential that all pipework, fittings and appliances be inspected and tested hydraulically to ensure the safety and efficiency of the system.
Before the start of any test the system should be visually inspected to ensure that the pipework has been correctly installed. The test procedure followed should be as recommended by the manufacturer or as stipulated by the approving authority.
6.5.4 Limitations
Plastics are not conductors of electricity and therefore no attempt should be made to use the pipework as a means of earthing electrical equipment.
Provision should be made for emptying pipes in exposed positions above ground or shallow buried pipes if they are not otherwise protected against frost damage.
6.5.5 Unplasticized PVC pipe
Above 20 °C water temperature and ambient temperature unplasticized PVC pipe (PVC-U) should be derated according to the manufacturer’s recommendations. -` ` , , ` ` ` , , , ` ` , ` ` ` , ` ` , ` ` ` ` ` ` , ` ` , -` -` , , ` , , ` , ` , , `
-PVC-U pipe may be supplied plain ended for jointing with separate couplings or supplied with
integral sockets already formed on one end of each pipe. Joints may be solvent cement, push fit
insertion or mechanical joint. Both push fit and mechanical joints offer little resistance to end thrust forces such as those set up at bends, junctions, valves, etc. The pipeline therefore should be
suitably anchored when these joints are used. The correct methods for completing the jointing of pipes and fittings as advised by the manu facturer should be followed.
Either saddles or tees may be used for service connections, the choice of the most suitable for each situation depends upon diameters used and site conditions.
Cold bending or hot bending of PVC-U pipes may be applied to allow changes in direction; either method requires skill.
The storage, handling and transport of PVC-U pipe should be as recommended by the PVC-U pipe manufacturer, taking care to protect against the effects of prolonged exposure to sunlight.
Installation of PVC-U pipe below and above ground should follow the manufacturer’s instructions. For above ground installations preventive measures should be taken to reduce the effects of freezing, expansion and heat and adequate support should be provided.
Before testing, anchor blocks should be allowed sufficient time to develop their strength, e.g. concrete to set properly. All intermediate control valves should be positioned open for the duration of the test.
The test should be deemed satisfactory if the quantity of water required to restore the required test pressure does not exceed the amount
recommended. The recommendation in the UK is as follows.
3 l per 1 000 m of pipe per 25 mm of nominal bore, per 3 bar of test pressure per 24 h.
Refer to BS 8010-1 for assessing the suitability of soil for surrounding buried pipes.
Details of working pressures, classes and wall thicknesses of PVC-U pipes may be found in the manufacturers’ technical data.
6.5.6 Polyethylene plastics pipe
6.5.6.1 Low and high density polyethylene plastics pipe
Low density polyethylene (LDPE) has a relatively low tensile strength and pressure pipes made from it are generally restricted to those of smaller bore.
High density polyethylene (HDPE) is rather stiffer and is a stronger material. Therefore the pipe walls are thinner and larger bore pipes at the higher pressure classifications are possible.
Polyethylene is not liable to attack from water or from soils which are corrosive to metals.
Polyethylene is an electrical insulator and cannot be used for earthing electrical insulations.
Polyethylene softens with heat and it is essential that it is not used for applications adjacent to heated surfaces. LDPE softens at lower temperatures than HDPE.
Polyethylene pipe may be laid in exposed positions without the need for special protection against frost damage, but will not prevent the water from
freezing in the pipe.
The outside diameters of the pipes are based on the outside diameters of steel pipes.
Polyethylene pipe may be jointed using
thermofusion techniques, compression joints, or threaded joints.
Bending of polyethylene pipe may be by either hot or cold techniques, hot techniques achieve tighter bends.
Polyethylene pipe may be laid satisfactorily by mole-plough providing the equipment is capable of maintaining the correct depth of cover over the pipe. The piping is liable to be cut by sharp surfaces above or below ground and therefore extreme care should be taken.
6.5.6.2 Medium density polyethylene pipe
It is a recommendation of the UK water industry that the use of blue medium density polyethylene pipe (MDPE) be adopted as the standard type of polyethylene pipe for underground water services in the size range up to and including 63 mm. In the size range over 63 mm the use of MDPE pipes is a matter of choice for the engineer and the end user. In this range of sizes MDPE piping is often
compared with PVC piping for both cost and physical advantages.
Although these recommendations do not apply to agricultural irrigation systems, the engineer or the end user may specify MDPE pipe.
Pipes up to and including 63 mm may be supplied in coils up to 150 m long, while pipes larger
than 63 mm may be supplied in 6 m, 9 m or 12 m lengths.
Jointing methods vary depending on the pipe diameter, but they include compression fittings, electrofusion methods and insert fittings.
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-6.6 Aluminium pipe
Aluminium pipe may be used for many above ground applications including portable supply mains, portable sprinkler lateral lines, and suction and delivery pipework on the pump unit.
The pressure rating of an aluminium pipe depends on its diameter, in general, the smaller the diameter of the pipe the greater is the maximum operating pressure that can be used for the system. Typical operating pressures are up to 12 bar for pipe
diameters up to 125 mm to 150 mm, and up to 9 bar for diameters above 150 mm. High pressure
irrigation systems may eliminate the use of aluminium pipe.
Friction loss in aluminium pipe is greater than in PVC pipe due to the slightly rougher surface finish of the pipe. Friction losses in the fittings vary according to the type of connection and the degree of resistance to flow that occurs.
The maximum advisable velocity in aluminium above ground portable pipe systems is
about 1.5 m/s depending upon system design parameters. A velocity may be used above this figure, provided that suitable precautions are taken in the design and specification of the pipe and fittings used.
The technical specification for aluminium pipe should detail wall thickness, wall tolerance, mean diameter, tolerance on mean diameter, bursting pressure, sag when full and denting factor
Reference should be made to the manufacturer to ensure suitability for the application.
Pipe couplings used with aluminium pipe may be quick couplers, flanged or sleeved.
Quick couplers, using a male and a female coupling to provide a connection between the lengths of pipe, should be easy to connect and disconnect and have efficient seals. The seals may drain down
automatically when pumping stops, facilitating pipe moving. Seals may be fast drain or slow drain, the selection of the correct type should be made to suit the application.
Flanged couplings provide a more permanent type of connection and would not usually be used in portable pipe systems.
Sleeve couplers (bolt up wedge type) may be used for the connection of aluminium piping. The sleeve coupler slides over the two plain ends of the pipe and bolts up to provide the seal connection. This type of coupling is more often used on the su ction pipe for the pump unit where aluminium piping is
employed. In this application it is essential that the seals do not allow air to enter.
The weight of aluminium pipe compared with lightweight galvanized steel piping is about 50 % of the weight of lightweight galvanized steel.
Aluminium pipes are therefore suitable for moving and installing by one man even with the larger diameters of pipe.
The loading capabilities of aluminium pipe are low and when the pipework has to span even a short distance, support should be provided underneath the pipe. The spacing and the type of supports depend upon the pipe diameter.
Aluminium pipe is susceptible to corrosion from certain chemicals; copper may be especially
damaging to aluminium pipe. It is a soft metal and therefore physical damage may easily occur if roughly handled.
6.7 Lightweight galvanized steel pipe
Lightweight galvanized steel pipes may be used for both portable supply mains and sprinkler lateral lines. This type of pipe may also be used for suction and delivery pipes on pump units.
A typical pressure rating for lightweight galvanized steel piping is a working pressure of 15 bar for pipe diameters up to 216 mm. The pipe may be suitable for higher pressure systems.
Friction loss characteristics of lightweight galvanized steel piping are similar to losses in aluminium pipe unless corrosion has occurred inside the steel piping.
The material for lightweight galvanized steel piping is specified by the manufacturer and should be to a suitable specification for irrigation applications. The commonly used couplings on this type of pipe are over centre latch couplers. A seal is achieved by levers holding the coupling tight and preventing any water loss.
The angle of deviation for lightweight galvanized steel pipes is usually 15° either side of the straight line position.
The seal provides effective sealing under vacuum and is suitable for the quick coupling connections required on portable suction assemblies.
Galvanized steel piping, if damaged on the galvanizing, is subject to corrosion and once the steel is exposed, rusting may occur.
The quality of the thickness and application method of the galvanizing is important for the pipe to ensure a long service life.
If the pipe is moved around continually on abrasive soils then the galvanizing may well be worn away and the steel exposed and corrosion could occur. Alternative pipe materials should be considered.
6.8 Steel pipe
Steel pipe is commonly used in suction and delivery assemblies for pump units, in road crossings,
hydrant risers and other applications both underground and above ground.
It is relatively inflexible and connection of fittings should be made with care especially where potential movement may occur.
Joints that may be used for steel pipe include sealing ring joints, flanges, butt welding, sleeve joints and threads.
The purchaser or designer should state whether the pipes and specials are to be protected against corrosion, whether the protection is to be external, internal or both, and the type or types of protection required. The types of coating commonly used in irrigation systems are bitumen applied hot or cold, epoxy or plastics based coatings, cold galvafroiding or equivalent.
Steel may be used to fabricate specials such as bends, tees and reducers for certain types of irrigation fittings.
6.9 Pipe fittings
The fittings described concentrate on those used for PVC pipe as this is the commonest type of material used for underground mains pipelines for irrigation systems in the UK.
Fittings for underground mains may be made from PVC material, cast iron, ductile iron, aluminium or steel.
The suitability of a specific material for the
application required will depend on the application in the field, manufacturer’s advice and customers’ preferences. The type of material used for the fittings will also affect the method of installation, ease of installation and resistance of the fitting to corrosion, etc.
Fittings may be complete with couplings or may be plain ended to be joined to PVC pipe or other fittings using separate couplings. Fittings complete with couplings are usually either cement joint (PVC), or mechanical joint (PVC fitting and joint or ductile iron, cast iron or aluminium).
The use of cement joint fittings is not recommended on fittings above 100 mm to 150 mm as it is likely that the cement applied to the fitting will have partially dried before the fittings can be connected together. It is therefore advisable that mechanical joints are used above 100 mm to 150 mm sizes
where seals make the joint instead of cement.
Separate couplings usually employ a mechanical joint to provide the connection between the two
plain ends of pipe and fittings. Bolt up wedge type couplers are often used for connecting PVC pipe and either steel fittings or cast iron fittings. The seal is achieved by tightening up wedges by clamps onto the two pieces of pipe or fitting. These types of couplers may connect different outside diameter pipes and fittings (stepped couplers). The coupler may be fitted with or without a centre register. Couplings without a centre register are used for repair of piping which is already installed in the ground. It is possible to slide the coupler all the way over the one section of pipe and then slide it back over the two sections of pipe to repair coupling. Push on couplers use a wedge seal at either end which seals automatically.
Connections between plain ended PVC pipe and flanges may be achieved by using either a flange adaptor which incorporates a bolt up wedge seal assembly or a stub flange which is cemented to the PVC pipe itself.
For smaller diameter pipes, unions may be used to provide a connection between PVC pipe and the fitting. Threaded unions cement joint onto the PVC pipe and thread connect onto the fitting
(valve, tee, etc.).
Bends may be fitted with or without couplings for connection to the PVC pipe. Bends may be either short radius, long radius or sweep bends.
Sweep bends or long radius bends are preferred for use on the larger diameters of pipe involved in PVC supply mains, giving better flow characteristics and less loss within the bend.
Short radius bends may be used on the smaller diameter sizes of pipe but care should be taken in their application. The normal bend angles available are 90°, 45° and 22.5°.
Tees may be provided with or without couplings and may have different connection types on their inlet and outlet. A typical application for tees within the underground mains would be where a spur connects to the main line. The tee may have either cement joints or mechanical joints if it is PVC or may use
mechanical couplings if the tee is of steel, cast iron, etc.
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