Drip irrigation system

applies water in low volumes uniformly along with the fertilizers onto or into the soil near the plant root zone. This involves several components. These are the network of pipes (main line, sub mains, laterals), emitting device called as drippers or emitters, control head consisting of pumps, filters and fertigation units; and other accessories such as valves, gages etc. The main line delivers water from water source with the help of pumping device or elevated water tank to the sub main and the sub mains to the laterals. The emitters which are attached to the laterals deliver water onto or into the soil for irrigation. Emitters are the end device of the drip irrigation system. 

The components of the drip irrigation system are classified into following principal categories:

a)      Pump and prime mover:

The pressure necessary to force water through the components of the system including fertilizer tank, filter unit, mainline, sub main, laterals and provide at the emitters at the desired pressure is obtained by a pump of suitable capacity or the overhead water tank located at suitable elevation.

b) Water source:

Water sources such as river, lake, reservoir/tank, well, canal water supply or connection to a public commercial or cooperative water supply network can be used. Drip irrigation is a pressurized irrigation technology in which water is delivered from these sources by increasing its internal energy (pressure) by pumping.

c)  Pipe network:

Mainline, submains and manifolds (feeder pipes) and laterals.

d) Emitting devices:

Emitters or drippers or the laterals integrated with drippers/emitters and line source with drippers.

e) Control devices:

Valves, flow meters, pressure and flow regulators, automation equipment, backflow preventers, vacuum and air release valves, etc.

f) Filtration devices:

Removal of suspended materials in the water. Media, screen and disc filters.

g) Chemical injectors:

For application of plant nutrients and water treatment agents along with the irrigation water. Pressurized tank, venture injector, injection pump.

The Source There are two alternative sources of water supply:

a) Direct withdrawal from surface source (such as a river, stream, pond or dam reservoir) or from an underground sources (such as a well). The pumping devices need to be installed for the withdrawal.

b) Connection to a commercial, public or co-operative supply network. If pumping is needed, the pump will be chosen according to the required flow rate and pressure in the irrigation 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.  

The Pumping Devices

The pumping devices are required to provide the pressure to pass water through the control head, different accessories and pipe network and then to the emitting devices at desired pressure. The pressure can be developed by using the elevated tanks or pumps. The elevated tanks can provide the pressure to the small system with micro tubes as the emitting devices. Other systems need the pumps. The pumps to be used may be centrifugal pump, submersible pump, turbine pumps. They may be powered by the electric motor or the diesel pump.

The Pipe Network

Main Pipes of mainlines are usually made of poly vinyl chloride (PVC) or high density polyethylene (HDPE). Ordinary PVC pipes have not UV protection and should be installed underground. Recently, unplasticized PVC (uPVC) pipes are manufactured with reduced sensitivity to ultra-violate (UV) rays and better endurance than ordinary PVC pipes. HDPE pipes can be installed inside or above ground, as they are impregnated with carbon black that provides protection against UV. The nominal working pressure of pipes has to be higher than that of the submain/drip laterals. The pipes of diameter 50 mm or above and the pressure rating of more than 4 kg/cm2 are used for mainline. The exact diameter and pressure ratings are decided in the process of design and depend on the size of the area irrigated, emitter operating pressure, topography, static and delivery heads etc.  

Submains

Submains are installed underground (PVC or HDPE) or above ground (HDPE only.) The pipes of diameter 32 mm or above and the pressure rating of more than 2.5 kg/cm2 are used for sub mainline  

Manifolds

In certain circumstances, when rows are very long or in rolling 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.  

Laterals

Laterals are the tubes on which the emitters are mounted or within which they are integrated. They are usually made of low density polythene (LDPE) or linear low density polythene (LLDPE) with features such as flexibility, non corrosivety, resistance to solar radiation and temperature fluctuation and generally black in color. Laterals usually have inner diameters in the range of 12 to 20 mm with wall thickness varying from 1 to 3 mm. The wall thickness is made to withstand pressure more than 2 kg/cm2 depending on the requirement. The laterals may be laid on the soil surface or underground. Laterals buried at 5-10 cm below soil surface is suitable to vegetables grown on hillocks or under plastic mulch. Laterals need to distribute the water uniformly along their length by means of drippers or emitters.

Valves Flow and pressure control valves

are required for controlling water distribution and regulating pressure in the pipeline. The valves used in drip irrigation systems include air release and vacuum relief valve, pressure regulating valves, flow regulation valves, non return valves and on hyphen and hyphen off valves. Manual or Automatic Flow Regulating Valves: Manual or automatic valves are used for the opening and shutdown of water and for splitting the irrigated area into subunits. Pressure Regulators or Pressure Relief Valves: These are used to prevent excessive pressure beyond the working pressure of the system. These are installed at any point where there is a possibility of existing excessively high pressure. Such kind of high pressure may be generated in the system from sudden opening and closing of the valves, starting and stopping of a pump. Closing and opening of the flow regulating valves gradually and using the air vents/relief valves at the proper location may prevent to generate the excessive pressure in the system. By pass assembly to bypass the excess water and pressure right at the source and pump could be adequate instead of pressure regulators or pressure relief valves. Check Valves and Backflow Preventers: 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. Air-Release/Relief Valves: Air-release/relief valves are installed at the higher elevation points of the system to prevent air flow in the pipes. These valves allow air to escape when filling pipelines with water and remove air pockets at high points in the system. 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. Vacuum Breakers: 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. Vacuum relief valves, which have orifices of size 25 to 200 mm in diameter, are designed to exhaust large volume of air during pipe filling and to close when the filling stops.   

Gages

Pressure gauges monitor water pressure in the system and ensure operating pressure remains close to the recommended or desired values. Based on where the pressure gauge is installed, it will measure water pressure in a various ranges, from 0 to 10 kg/cm2 near the pump to 0-2 kg/cm2 at the end of drip lateral. Pressure gauges may be installed at set points (near the pump, before and after the filter, near the field). They can also be mounted as portable devices and installed temporarily at the end of a drip lateral.

Water Meters

Water meters monitor and record the amount of water moving through a pipe where the water meter is installed. When a stopwatch is used together with a water meter, it is possible to determine the discharge in the system.

 Control Head

The main components of the control head are the filtration and chemigation units