Chapter 1 Drip irrigation components.pptx

Understand the working principles and hydraulics of all the components of drip irrigation such as drippers, filters and fertigation equipment

1. Pressurized (Drip) Irrigation I EiT -M, School of Civil Engineerin g, IEC October, 202 4

2. 1 . Drip irrigation components Contents Introduction Salinity under drip irrigation Emitter/dripper Filtration Chemical injection devices Pipes PVC fittings and accessories

3. Objectives At the end of the chapter, students will be able to: Understand the working principles and hydraulics of all the components of drip irrigation such as drippers, filters and fertigation equipment

4. Introduction Drip irrigation is a system in which water is applied as drops at the root zone of plants (Fig. 1). In drip irrigation system, irrigation is done at frequent time intervals . Water advances on the soil around a dripper only after the amount of water applied exceeds the infiltration rate at a point. Typically, a dripper wets a diameter from 20 to 120 cm depending on the soil type. The depth of wetting for any specific soil primarily depends on the time of operation of the dripper. Fig. 1: Water emission device Definition

5. Introduction Drip irrigation components include (Fig. 2): Pump, Pipes, Filters, Fertigation devices, Water emitting devices, Flow control equipment, and Fittings and accessories. Definition Fig. 2: A typical layout of drip irrigation system

6. Introduction Advantages of drip irrigation Drip irrigation has many advantages and also has few disadvantages. Advantages Only root zone is wetted and percolation losses are negligible Conveyance loss is less Weed growth is less Laborer requirement is less Salty soils can be irrigated Salty water can be irrigated Fertilizers can be applied through irrigation water Increase in yield of crops.

7. Introduction Disadvantages Costly The drippers get clogged over a period of time. So, periodic maintenance is necessary

8. Salinity Under Drip Irrigation In drip irrigation, the salt concentration of soil solution can be maintained nearly equal to the salt concentration of the irrigation water. Salt is transported to the periphery of wetted front in drip irrigation (Fig. 3) Fig. 3: Salt build-up in drip irrigation Since salt build-up is away from the root zone, plants do not get affected very much. Sometimes in saline lands under drip irrigation when a light rainfall occurs, the salt build-up tends to move into the root zone. Under such situations plants show wilt symptoms. Under such situations, after small rains, drip irrigating the crop sufficiently well would again transport the salts out of the root zone.

9. Emitters or Drippers Emitters are the devices, through which water comes out of the pipe network . The emitters dissipate the pressure of outcoming water. The pressure dissipation is brought about by turbulence, vortex and friction along the path of the flow. Normally the drippers are specified with dripper discharge rates 2 l/h, 4 l/h, etc. Based on connection to the lateral, emitters/drippers can be classified in to: Online dripper and Inline dripper

10. Emitters or Drippers Online Drippers Online drippers are attached on the lateral by drilling a hole and inserting into the lateral by hand (Fig. 4 ). Mostly online drippers are used for widely spaced tree crops . Sometimes, a microtube start is inserted into the hole, microtube is attached to the microtube start, and dripper is attached at the end of the microtube (Fig. 5 ). This kind of microtube connections are needed when many drippers are provided to each tree Fig.4: Online dripper Fig.5: Microtube emitter

11. Emitters or Drippers Online Drippers For tree crops when large application rate is used, at the end of the microtubes, no dripper is fixed. The microtube discharges at around 50 liters per hour (l/h). This discharge rate is higher for most soils and cause runoff. Hence in order to prevent runoff, trenches or bunds around the tree are formed (Fig. 6 ). Fig. 6: Microtube emitter with a trench around tree

12. Emitters or Drippers Inline drippers When drippers are either placed inside the lateral pipes or on the walls of lateral pipes, they are called as inline drippers. The spacing between them is fixed while manufacturing itself. They are available in the market with different spacings and discharge rates. In case of thicker walled lateral pipes, the inline drippers are made as hollow drippers and placed as shown in Fig. 7. Fig. 7: Inline dripper—hollow full round

13. Emitters or Drippers Inline drippers In case of flexible thin walled lateral pipes, the inline drippers are placed on the wall of the lateral as shown in Figure 8. They are very much useful in row field crops and small tree crops. Fig. 8: Inline dripper—on the wall

14. Filtration If sufficient care is not given in the selection of components and operation of drip irrigation, drip irrigation would become an undesirable option due to clogging problem. But nowadays, the filtering technology combined with electronics has grown well to deal with this problem satisfactorily. Filters are used for removing the physical impurities in the water to prevent clogging of emitters. The nature and the magnitude of impurities is essential information before filter selection is done. Table 2 shows different physical, chemical and biological impurities in water those are normally tested. Based on the magnitudes of the impurities, the water is classified into three classes. If the plugging potential of water falls in moderate and severe ranges , the filtration process must be carefully done.

15. Filtration Factor Plugging hazard based concentration Concentrations Slight Moderate Severe Physical Suspended solids (filterable) (ppm) <50 50 – 100 >100 Chemical pH <7.0 7.0 – 7.5 >7.5 Dissolved solids (ppm) <500 500 – 2000 >2000 Manganese (ppm) <0.1 0.1 – 1.5 >1.5 Iron (ppm) <0.1 0.1 – 1.5 >1.5 Hydrogen sulphide (ppm) <0.5 0.5 – 2.0 >2.0 Hardness a (ppm) <150 150 – 300 >300 Biological Bacteria (population) <10,000 10,000 – 50,000 >50,000 Table 1: Criteria for plugging potential of micro irrigation water sources

16. Filtration Generally, all particles larger than 0.075 mm should be filtered. It is recommended that all the particles greater than 1/10 th diameter of flow passage in dripper be removed if the water contains significant amount of biological impurities because individual particles tend to collect together and plug the emitters. When water contains significant amounts of particulate matter, at least the particles larger than the flow passage in emitters must be filtered. Debris screens are simple screens at the inlet of suction pipe of pumps which prevents debris from going into the micro irrigation system. For surface water sources such as canals, rivers and lakes, desilting basins are used for settling silt by allowing water in a surface tank where in velocity of flow is sluggish.

17. Filtration Types of filters Filters are normally divided into four types. Vortex sand separators or hydro cyclones Media filter Disc filter Screen filter

18. Filtration Fig. 11: Sectional view of a vortex sand separator Vortex Sand Separators (Hydro Cyclones) These filters can be used to separate sand particles which are between 70 and 300 µm from water. A typical sand separator is shown in Fig. 11 . In these filters, water is made to rotate , and because of the centrifugal force , sand particles are separated out. The sand particles hit on the wall of the filter and helically fall down in a collection chamber at the bottom of the filter. A screen filter is used as a secondary filter to filter out the impurities that escape from it.

19. Filtration Sand filters are used when water contains primarily organic impurities like algae, slimes and fine suspended particles. In case of water with ferrous impurities , settling basins are used to convert ferrous form of iron into ferric form by the action of microbes in the atmosphere. They form colloidal slime like substances and they are usually filtered by media filters. During normal filtration process in the media filter, the water is made to pass from top to bottom through the media placed in a mild steel tank (Fig. 12). Cleaning of filters is done by backwashing of the filter by directing the water flow from bottom to top. Fig. 12: Sand filter in normal & backwash modes Media Filter

20. Filtration Media Filter In media filters crushed granite or silica sand is used as filter media. The crushing process yields sharp edged particles capable of trapping linear filament like algae easily. Uniform sized particles are preferred rather than graded mixture. When graded mixture is used, there is a possibility of filling of larger pores by smaller sized particles. Sometimes naturally available pea gravels of uniform size are also used but there is a slight disadvantage in such use that due to the smoothness of the particles the filtering efficiency is relatively less. Usually in media filters, air valve is an integral part due to the possibilities of heavy pressure surges during cleaning operation. Table 3 shows the characteristics of different types of media normally used.

21. Filtration No. Sand media designation Mean effective size (µm) Screen equivalent (No of opening /inch 2 ) App. Size of aperture (µm) Pressure drop when clean (m) Recommended discharge rate during back flow (l/s/m 2 of sand bed) 1 #8 crushed granite 1900 100 – 140 160 1.5 – 2 Material-escape less likely 2 #10 crushed granite 1000 140 – 180 80 17 3 #16 Silica sand 825 150 – 200 60 14 4 #20 Silica sand 650 200 – 250 40 2 – 3.5 7 – 10 5 #30 Silica sand 340 250 and more 20 Table 2: Characteristics of different types of media normally used.

22. Filtration Disc filter was invented in order to overcome the problems in media filters such as they have big and sturdy containers, they need more quantity of water and more duration for backwashing. They contain numerous discs with diagonal grooves, and the discs are placed one over the other; mechanical pressure is given by a spring-loaded nut , and narrow gaps get formed between the discs. The cross section of the gap changes along the flow direction of water between the discs (Fig. 13). Fig. 13: Disc filter in normal & backwash modes Disc Filter

23. Filtration Disc Filter Water moves radially inwards towards the center . Due to the tortuous flow occurring in between the discs, the dirt keeps moving in between the discs and gets trapped between the discs somewhere Various types of disc filters are available to filter the dirt in the range of 25–800 µm. Disc filters also come with a provision of backwash facility and during the process, the mechanical pressure on the discs is removed and the discs are made to rotate , and the dirt gets washed out of the discs. Disc filters are useful to filter if moderate level of organic matter exists in water. This filter may cause a pressure head loss of 2–3 m.

24. Filtration Screen Filter Screen filters are the most commonly used type of filter and is the earliest invention. Even if the water does not contain any visible impurities , this filter is recommended. In this filter, the essential element is filter screen . Water enters into the filter body through filter element and passes through the outlet. Nylon mesh or stainless-steel mesh is used. Nylon mesh can be made to flutter easily during backwash. The disadvantages of nylon mesh are that it does not last longer than stain less steel mesh and also the surface area needed for any specific discharge rate is approximately double that of stain less steel filter (Fig. 14). Screen filters are prone to get clogged even when there is a slight increase in organic load.

25. Filtration Screen Filter Fig. 14: A simple screen filter As an alternative to media filter and disc filter, screen filters also come with advanced sophistication to automatically remove filter cakes on the screen surface automatically. A typical auto rinse screen filter is shown in Figure 15 . Fig. 15: Automatic self-cleaning filter

26. Filtration Screen Filter Water entry in the filter is at the bottom and then through cylindrical screen element flow inside out. Water from the inlet passes through nozzles and leaves the dirt over the screen and passes out of the screen. When the differential pressure between inlet and outlet goes above a threshold, a rinse cycle is started and is ended with in few seconds. During the rinse cycle, the rinse valve opens causing the pressure in the rinse chamber to fall down. Through the nozzles, water movement would occur from the high pressure-filtering chamber to the rinse chamber. Hydraulic motor in the rinse chamber gets rotated due to the water flow through the rinse chamber. This rotation causes the dirt collector also to rotate.

27. Filtration Screen Filter When water flows in reverse direction with a velocity through the screen, the deposited impurities on the inner side of the screen goes through the nozzle and enter the rinse chamber. Pressurized water is used in the piston on top of the filter to hold the dirt collector to its lowest position. Pressure in the piston is released during rinse cycle. The dirt collector goes slowly up, and during this upward movement, nozzle also is able to collect impurities throughout the inner area of screen. The maximum recommended flow rate for screen filters is 135 l/s per m 2 of screen open area. Screen filters with various screen openings are available to filter the dirt in the range of 70–300 µm. Screen filter may cause a pressure head loss of 1–2 m.

28. Filtration Filter Selection Table 3: Filter selection guide S. NO. Factors of water contaminants Recommendation Alternative 1 Sand particles Hydro cyclone &screen Screen 2 Suspended solids (<50 mg/l) Disc Screen 3 Suspended solids (>50 mg/l) Media &disc Media & screen 4 Algae and organic matter (low) Disc Screen 5 Algae and organic matter (high) Media & disc Media & screen 6 Iron & manganese (<0.5 mg/l) Disc Screen 7 Iron & manganese (>0.5 mg/l) Media &screen Disc 8 Hydrogen sulphide (<0.5 mg/l) Disc Screen 9 Hydrogen sulphide (>0.5 mg/l) Media & screen Disc

29. Pipes Pipe section which carries water from control unit to field is called as main pipe. The pipeline connecting the Main for each field is called as submain or manifold. Usually, just before the connection of any submain, a control valve and an Air valve need to be provided. Additionally, a pressure control valve and pressure gauge along with a secondary screen filter would also help improve the performance of the system (Fig. 16 ). Fig. 16: Main to submain connection options.

30. Pipes Laterals are the pipes connected with the submain. A submain along with a group of laterals and drippers is called as one Subunit. A subunit can be operated separately independent of the other subunits. Main and submains are usually PVC pipes. PVC pipes are specified by external diameter sizes of 20 mm, 25 mm, 30 mm, etc. Usually 0.25 MPa to 4 MPa strength of pipes are used for drip irrigation. The PVC pipes have to be buried under the land. It should not be laid over the ground. If it is laid over the ground, it gets affected by ultra violet rays of the sun and it will become brittle and will get broken in a few years. Sometimes High-Density Poly Ethylene (HDPE) pipes are also used. They can be laid over the land. But they are costly compared to the PVC pipes.

31. Pipes Laterals are always made of Linear Low-Density Polyethylene (LLDPE) pipes. The laterals are laid over the ground in surface drip irrigation and laid below the ground in subsurface drip irrigation. Holes are drilled in the submains with drill bits. Then a start washer is inserted in to the hole and a start connector is driven into the washer using a wooden hammer. The lateral pipe is inserted over the start connector. The laterals are closed at the end by folding the lateral pipes at the ends and fixing an accessory called as lateral end block. Lateral pipes are specified with outer diameters. They are available in sizes of 8 mm, 12 mm, 16 mm, 20 mm and 25 mm. Lateral pipes are available with pressure rating of 0.1 Mpa , 0.125 Mpa , 0.25 Mpa and 0.4 Mpa .

32. PVC Fittings & Accessories Fig. 17: PVC fittings & accessories The delivery ends of pumps are Galvanized Iron (GI) pipes. GI connections are threaded. All the drip irrigation system fittings are made of PVC and these connections are made using an adhesive known as solvent cement. So, in order to connect drip irrigation system with the delivery end of pump either an FTA (Female Thread Adaptor) or an MTA (Male Thread Adaptor) is needed. If the GI delivery end has an external thread, FTA is connected. If the GI delivery end has an internal thread, MTA is used.