Drip/Microirrigation System Componenets
This page describes the components of the drip/microirrigation system presented in figure 1 below. Beginning at the water source and going with the water flow all the way to the drip emitter, details of the system components and their accessories will be presented in the following order:
* Water source & pump
Water is pumped from the source and pressurized to enable it to flow through the system under pressure. Two principle types of pumps are ususally used for pressurizing the water: centrifugal pumps and turbine pumps. The first type is used for pumping water from shallow water sources (less than 20' deep) like lakes and ponds and the second type is used for pumping water from deep sources,e.g., wells.(Courtesy of Cornell Pump)
* Main filter
The pressurized water discharged from the pump flows through the main filter to remove the particulates carried by the flow that could clog drip emitters. Two principal types of filters are commonly used for this purpose, sand media filter and screen filter. The first type is significantly more expensive than the second one. However, sand media filters are more suited for water with heavy loads of fine sand and organic particulates (e.g., canal water); while screen filter may be used for filtration of ground water low in organic particulates.
* Mainlines and sub-main lines
The filtered water flows under pressure into the system main and sub-main conduits to different blocks in the field. A block is an irrigation unit controlled by a separate shutoff valve (see Fig.1). PVC pipes are usually used for constructing the main and sub-main lines. These lines are fitted with shutoff valves and various specialty valves to control the flow and to protect the lines against pressure surge and other adversities.
* Manifolds and lateral lines
Sub-mains feed the manifolds that intern feed the laterals or emitter lines connected to it. The manifold and the emitter lines that it feeds make a block (see figure 1). A control head (see figure 32) is constructed at the inlet of each block to regulate the water flow from the sub-main line to the manifold. The manifold feeds several emitter lines as one block of laterals. In addition to the shutoff valve, the control head is equipped with air vent, ports for measuring water pressure, screen filter and pressure regulating device. The pressure-regulating device is used to set the water pressure, at the inlet of the manifold, to the design value such that the average operating pressure for all emitters on all laterals in the block is essentially the same.
Emitters are the devices that deliver water and chemical (e.g., fertilizers) directly to the plant. They are mounted alongthe laterals either in-line, on-line or imbedded in the laterals (drip lines and drip tapes). Laterals could be laid on the ground (surface drip)or buried below the ground surface (subsurface drip).
Figure 1. Drip/microirrigation system layout
A: Water Source & Pump
Water flows through drip/microirrigation system under pressure (higher than atmospheric). Usually horizontal centrifugal pumps and deep-well turbine pumps are used to pressurize the irrigation water as indicated above. Centrifugal pumps are used to pump water when the suction lift i.e., the vertical distance from the water surface level to the center line of the pump (see Fig. 3), is 20 feet or less, at see level. This maximum suction lift decreases with the increase in elevation above sea level because of the decreases in atmospheric pressure with elevation. Turbine pumps are used for pumping water from greater depths (e.g., deep wells).
1. Cenrifugal Pump
Figure 2 shows a cutaway of a centrifugal pump and figure 3 illustrates the general setup for the installation of such pump. Figure 4 shows some details of the components on the suction side of the centrifugal pump, while figure 6 provides similar illustration for the discharge side of the pump.
a) Suction Side
It is important to notice, as illustrated in figure 4, that the suction line is enlarged (selected to be larger than the inlet diameter of the pump) to reduce the head loss on the suction side, this enhances pump performance. Moreover, the use of the eccentric taper minimizes air accumulation and this is critically important since the accumulation of air in the suction line could lead to the pump deterioration and to the degradation of system performance. Also notice that all connections are flanged to minimize head loss (compared to threaded connections) to improve the energy efficiency of the system. Installation of foot valve at the inlet to the suction line (figure 5) is necessary to maintain pump priming as explained below. To summarize, avoid air accumulation and minimize head loss in the suction line to maintain satisfactory pump performance and to improve energy efficiency of the system.
Figure 2. Cutaway of centrifugal pump
Figure3. Centrifugal pump setup
Figure 4. Suction side of the centrifugal pump
(Courtesy of Cornell Pump)
Figure 5. Foot valve and installation on the suction pipe of the centrifugal pump
(Courtesy of APCO valves)
The foot valve is installed in the vertical position with the direction of flow upwards. In this position the foot valve is in the normally closed position. Prior to the normal start up of the centrifugal pump it is recommended to manually fill the suction line with water. In this way risk of damage to the centrifugal pump from running dry is eliminated. Once the suction line is filled the foot valve takes over and opens while the centrifugal pump is running and closes when the pump stops running to maintain a flooded suction and primed pump.
b) Discharge Side
The discharge side of the pump (figure 6) also shows the enlargement of the pipe size to reduce head loss (i.e., lower energy consumption) through concentric taper. Here a concentric rather than eccentric taper is used because air accumulation is not as critical on the discharge side as it is on the suction side. However, air vents are usually installed on the discharge side of the pump to get rid of air in the lines as will be shown later with turbine pump. All connections are flanged for the same above-mentioned reason. Other components, such as the check valve, shutoff valve and flexible coupler, on the discharge side are also installed on the discharge side of the turbine pump and will be discussed there.
Figure 6. Discharge side of the cenrifugal pump
2. Deep Well Pump
a) Suction Side
Figure 7 shows the details of the suction side of the turbine pump. The impellers of this pump are submerged under water thus there is no concern for the pump to run dry (i.e., no need to prime the pump).
Detailed Pump bowls (stages) schematic
(Courtesy of American Turbine)
Figure 7. Suction side of turbine pump
(Note that impellers are submerged under water)
b) Discharge Side
Figure 8 shows the details of the discharge side of the pump. The appurtenances on the discharge side is presented in figure 9, and will be explained next since they may require the frequent attention of the system operator and that also applies to the centrifugal pump.
Figure 8. Discharge side of turbine pump
Air/vacuum valve (air vent, Fig. 9), an on-line valve, is installed as close as possible to the pump discharge outlet to enable the escape of air that enters the system from the pump column while the lines are filling during the pump start. Air bubles in the lines reduces the size of the flow path thus lowers efficiency, and the sudden burst of air bubbles could cause a surge pressure that could compromise the integrity of the lines. Air vent also allows air entry when the pump is shutting off to protect the lines from developing vacuum after pump shutoff. Vacuum in the line could lead to pipe collapse or separation and discontinuity of water column. However, air/vacuum valve do not open to exhaust the small pockets of air which collect in the line while it is operating under pressure, for that pupose automatic air release valve should be used as will be explained later under “Mainline and Sub-mains” section.
Concentric taper is used to increase the line size, by at least one nominal size (e.g., 6” to 8”), to minimize head loss as previously explained.
Double-door check valve, an in-line valve, is used to act as automatic shutoff valve and as a one-way valve to prevent reversing the flow and draining of the system when the pump is turned off. It also prevents the reversed-flow from turning the pump in the opposite direction and that could damage the pump.
Pressure relief valve, is an automatic on-line valve, installed downstream from the check valve. The pressure relief valve releases water from the pipeline when the pressure in the line reaches a preset value to protect the lines from excessive pressure e.g., pressure surge. The cover on the valve (see Fig. 9) is used to protect it from the elements.
Gate valve is an in-line valve, acts as an isolation or shutoff valve, to allow servicing the other valves. Gate valve is also used as a rinse valve to allow taking water samples from the well (e.g., for analysis) while the isolation valve is closed, before water flows in the system. It is also used to help setting the backwash flow rate for the media filter (see Maintenance page).
Flexible joint (e.g., dresser coupler, see Fig. 9) is installed to release forces due to inner pressure, e.g., pressure force when starting the system, to secure the safety and integrity of the lines.
Propeller flow meter is an indispensable tool for irrigation management to determine the volume of applied water and the system flow rate.
A port is provided to measure the pressure on the discharge side of the pump using the pressure gauge shown in figure 9. A fixed pressure gauge may also be used for this purpose.
Two other ports are provided for chemical injection (e.g., fertilizers, pest control, acidification, chlorination). These two ports should be at least 3 feet apart to avoid mixing acid and chlorine when injected concurrently for controlling microbial growth in the system (see Maintenance page).
Similar set of valves and equipment could be installed on the discharge side of the centrifugal pump.
Air/vacuum valve Double-door check valve Iron gate valve
(courtesy of APCO valves) (courtesy of ITT valves)
(courtesy of Waterman Valves)
Propeller flow meter (courtesy of McCrometer) Air/Vacuum valve (Courtesy of Waterman)
Figure 9. Valves and measuring devices on the discharge side of the pump
B: Main Filter
Clogging of emitters is the most serious problem to be encountered with drip/microirrigation. Suspended solid particulates carried by the flow of water can plug emitters. These particulates are both organic (e.g., bacteria, algae, snails) and inorganic (e.g., sand and soil particles). Filtration of irrigation water is the most effective protection against clogging. Types of main filters commonly used for drip/microirrigation systems are screen filters and sand media filters. They are usually located next to the pumping plant.
Small screens are also installed at the inlet to each lateral (lateral inlet screen, Fig. 10) and strainers (in-line screen, Fig. 11) are installed at control heads at the inlet to the manifold that feed the lateral lines (see Fig. 1 & 33). These screens and strainers stop debris that may enter the lines if any breakage happens downstream from the main filter. In addition, sand separators and settling ponds are used to remove extra heavy loads of sand from irrigation water prior to pumping it into the system.
Figure 10. Lateral inlet screen Figure 11. Inline screen filter
1. Sand Media Filters
Pressurized water discharged from the pump enters the “inlet” of the sand media filter (see Fig. 12). The filtering media (sand) is cleaned periodically by backwashing i.e., reversing the flow direction through the media, one filter tank at a time (see Fig. 16). Many sand media filters are equipped with automatic backwash. While a tank is being backwashed the other tanks supply the needed clean water for both the backwash and irrigation. To review filter setting and maintenance procedures visit Maintenance page.
Figure 17 shows the actual field installation of the sand media filter. The filter inlet is fed from the pump discharge, the filter outlet is coupled to the inlet of the system mainline to deliver filtered water for irrigation, and the backwash line is for disposing the backwash flow carrying the filtered-out particulates. Notice the air/vacuum valve installed on the inlet line of the filter to avoid air accumulation or vacuum development in the line as previously explained. Also notice that the filter tanks are installed on a 6-inches concrete pad.
The capacity of the filter can be increased, depending on the system requirements, by adding extra tanks as shown in figure 13. Groove coupling (victaulic) is usually used for connecting the lines of consecutive tanks (see Fig’s. 12 &14). Butterfly valve with gear or lever operator is used as a shutoff or isolation valve on the outlet line of the filter to the mainline of the system (see Fig’s. 15 &17).
Figure 12. Sand media filter
Groove coupler (victaulic coupler) Groove coupler installation
Figure 14. Groove (victaulic) coupler for coupling filter tanks together
Figure 15. Field installed sand media filter
Figure 16. Schematic of filtration and backwash of sand media filter
Figure 17. Butterfly valves for above ground and under ground operation (Courtesy of Waterman)
* Butterfly valves are used as an isolation valves and on/off valves
2. Screen Filters
Screen filters can remove very fine sand and some of the organic particulates (e.g., algae) from irrigation water. Details of screen filter and water flowing through it during the filtration and backwash cyclesare shown in figure 18, while the stainless steel screen is shown in figure 19. The filtration capacity can be increased by adding more filters as shown in figure 20 and previously explained with the media filter
Figure 18. Screen filter, during filtering (up) and backwash (down)
(Courtesy of Yardney filters)
Figure 19. Screen filter cartridge
Figure 20. Screen filter set (Courtesy of Yarney Filters)
* It is important to remember that there should be no metal pipes downstream from the filter to avoid emitters clogging by metal debris.
* Chemical injection, e.g., fertilizers (see figure 8) may be done upstream from the filter to filter-out any precipitates that may form due to any chemical reaction to avoid their emitter-clogging effect. The effect of chemicals in the backwash flow of the filters on the environment should be taken into consideration. Local authorities should be consulted regarding this matter. Injection could also be done downstream from the filter if the used chemicals could cause deterioration of tanks or other components of the filter system. The filter manufacturer should be consulted regarding the tolerance of the filtering equipment. It is advisable to use water soluble fertilizers whenever possible.
C: Mainlines and Sub-main Lines
The filtered water flows under pressure through the system main and sub-mains PVC conduits, then to different blocks in the field as displayed in figure 1. The installation of these conduits is preceded by the trenching process to open the ground for the underground installation of these lines, according to the design plan, and figure 21 depicts this process.
1. PVC Pipes
Generally, Main, sub-main and manifolds are constructed of PVC pipes. These pipes are manufactured with either of two types of joining connections; solvent-weld pipes (see figure 25) and the gasket pipes (see figures 22, 23). Gasket-joints provide some advantages over solvent-weld joining. Gasket-joint are watertight, virtually leak-free and easy to install and assemble. They can be filled, tested and placed in service immediately after assembly while solvent-weld joints may require hours and sometimes days before being completely cured and ready for testing. Gasket-joints also provide allowance for thermal expansion and contraction of PVC pipelines while solvent-weld joints would require certain installation requirements to avoid the effect of temperature fluctuations on the integrity of the joints. PVC pipes are branched and fitted for installation of valves by means of the PVC fittings shown in figure 26.
Figure 21. Trenching and PVC pipe installation
Figure 22. Gaskted PVC pipe Figure 23. Installation of Gaskted connection
Figure 24. PVC pipe cutting Figure 25. Installation of solvent
Figure 26. Fittings for PVC pipes
After trenching and installation of the main and sub-main these PVC conduits are branched, to convey water flow to different blocks in the field, and fitted for installation of valves. These valves include shutoff for flow control and some specialty valves to guard against excessive pressure, air accumulation or vacuum development in the lines. These valves are listed next:
Butterfly valves (shutoff valves)
This valve and its function were explained earlier under “Sand Media Filter” and presented in figure 17.
Pressure relief valve
This valve and its function were explained earlier under “Turbine Pumps" and presented in figure 9.
This valve and its function were explained earlier under “Turbine Pumps” and presented in figure 9.
Automatic air release valve
This is an on-line valve, it has the ability to open automatically while the pipeline is under pressure to allow the small pockets of air that accumulate at high points to escape (see figure 28).
Combination air/vacuum & air release valve (figure 27)
This is an on-line valve, it combines the two basic functions of air/vacuum valve and the automatic air release valve.
It is composed of a gate valve (figure 27) installed on a male adapter (see figure 29) at the end of the line to enable flushing out any debris that may accumulate in the line (see figure 30 for details of installation).
Figure 27. Combination Air/vacuum Figure 28. Figure 29.
& continuous air release valve Air release valve Bronze gate valve
(Courtesy of GA Industries) (Courtesy of PGL)
See figure 31 for the suggested locations of air valves along the lines
Figure 30. Example for flushout installation
Figure 31. Where to install air valves
D: Manifolds & lateral lines
Water flows under pressure through the main, sub-main lines and then to the manifolds. Manifolds branch from the sub-main lines (see figure 1). The branching point is equipped with a control head (see figure 32) for shutoff, isolation and specially for regulating the inlet pressure to the manifold and the laterals branching from it in the block. Other functions for the control head include secondary filtration and air venting as mentioned earlier. PVC pipes used for constructing the manifold are usually in the range of 1” to 3” nominal size. In this size range solvent-weld and threaded fittings connections are commonly used for connecting and branching the pipes. Teflon tape is used for tightening the threaded connections. The instructions for using Teflon tape are illustrated in figure 33.
Figure 32. Details of control head at manifold inlet
(reference to control head in figure 1)
Figure 33. Instruction for installation of Teflon tape for threaded fittings and connections
2. Lateral lines (laterals) and emission devices
Sub-mains convey pressurized water to the manifolds. Lateral lines branch from the manifolds as shown in figures 1 & 32. Lateral lines are mostly made of Polyethylene (PE). Two principal types of laterals are used for drip/microirrigation, drip tubing and drip tape.
a) Drip tubing
The inside diameter (ID) of the PE drip tubing ranges from about 5/8” to 1” with wall thickness between about 0.05” to 0.07”, the larger the ID the larger the wall thickness. On-line emitters are manually installed on these lines. In-line emitters are similar in function to on-line emitters but they are pre-inserted into the PE tubing at specified intervals during the tubing extrusion process and referred to as emitter lines or drip lines (see Fig’s 34 & 35).
Emitter line (drip-line) PE drip tubing
Figure 34. Drip-lines and PE tubing
Details of drip-line (in-line emitters) On-line emitters (on PE tubing)
Figure 35. In-line and on-line emitters
Emitters are installed to discharge upward to avoid clogging of emitter orifice if any particulates are carried with the flow. If the emitter is installed to discharge downward these particulates are more likely to clog the emitter narrow passages.
In-line and on-line emitters are commonly used for irrigating tree crops though they could be used for irrigating other row crops. On-line emitters are manually installed to suite the plant spacing and the desired water distribution. They can be removed for checking and cleaning. In-line emitters are mostly factory installed at a given spacing and may exist where unneeded and cannot be removed from the lines, however, they save the labor and time needed for manual installation. Drip-line may be installed below the surface such that the soil surface may be kept dry. On-line and in-line emitters range in discharge from 0.5 to 2.0 gph (gallon per hour) per emitter.
Jets are another type of emitters. They are generally used for watering tree crops, like almond, that require light water application with large foot print pattern. They may also be used for watering crops grown in soils of low water holding capacity like sandy soils. The spray diameter ranges from 10’ to about 30’ with a discharge rate from 5 to about 25 gph. Different wetting patterns are available (e.g. full circle, butterfly) to accurately apply water only where wanted, such as enveloping each tree in an orchard without wetting the trunk.
Micro-sprinklers emitters are similar to jet emitters except that they emit water in full circle spray/sprinkler pattern only via a rotating spinner. These devices are attached to the PE lateral tubing similar to jets (see Fig. 36). Their advantage is that water is applied over a larger area using only one emission device, and that operating pressures and application rates are low. Possible drawbacks are that water is may be applied to non-target areas such roads, tree trunks and foliage and is affected by wind.
Jet with Tee-connection (fixed) Jet with barb-connection (adjustable)
(courtesy of Bowsmith)
Jet full circle Microsprinklers
(courtesy of Bowsmith) (courtesy of Nelson Irrigation)
Figure 36. Jets and Microsprinklers and modes of installation
Compression fittings presented in figure 35 are used for connecting drip tubing. These fittings are characterized by full flow pattern and ease of installation. The connection patterns for these fittings are shown in figure 36.
Figure 37. Compression fittings (Courtesy of Agricultural products)
Figure 38. Compression fittings connections
c) Drip tape
Drip tape laterals are “line-source” compared to on-line and in-line emitters that are considered “point source”. Line source provides a continuous line of soil wetting, while point source wets a limited area of the soil around the emitter. Drip tapes are made of PE material thinner than drip tubing and come in different thicknesses of 4 mil (1 mil = 0.001 of an inch) 6, 8, 12, 15, and 25 mil. Thick tapes are more expensive than thin ones. The 4 mil tape is commonly used for watering short season crops, e.g., strawberries, in medium textured soils, the medium thickness tapes are recommended for double cropping and long season crops, e.g., sugar cane and cotton, while the 25 mil tape is used for watering permanent crops like trees and vines. The thick tape is also recommended for using in coarse and rocky soils and where insect and rodent damage is possible.
The discharge rate of drip tape is expressed in units of gpm/100 ft (gallon per minute per 100 foot). Water is distributed evenly along the length of the tube. Drip tape discharge rate ranges from 0.2 to 1.3 gpm/100’ and outlet spacing along the tape is between 4” to 24” to accommodate the requirements of various crops and soil conditions. Tape ID varies between 5/8” to 1-3/8”. Rolls of tape come in different lengths, e.g., 1000’, 1500’. A roll of drip tape mounted on the tractor installation tool is shown in figure 39 and two types of tape are presented in figure 40.
Drip tape can be installed above or below the ground, and may be retrieved for multi-season reuse or disposed at the end of each season. Drip tape is relatively inexpensive and is used extensively for irrigating vegetable and field crops and under plastic mulching (as with strawberry). Some buried tape may last as long as ten years.
Figure 39. Drip tape and blade mounted on tractor tool bar for subsurface installation
Ro-drip (drip tape)
Chapin (drip tape)
Figure 40. Different types of drip tape
Tape lock fittings shown in figure 41 are used to connect drip tape. These fittings provide tight, fast, reliable leak proof connection on thin wall tape and their connection patterns are shown in figure 42. Spin lock fittings, shown in figure 43, are also used for connecting drip tape, they provide lock-type fittings that accept a wide range of hose I.D.s and wall thicknesses, their connection patterns are shown in figure 44.
Figure 41. Tape lock fittings for drip tape (Courtesy of Agricultural products)
Figure 42. Tape lock connections
Figure 43. Spin lock fittings for drip tape (Courtesy of Agricultural products)
Figure 44. Spin lock connections
Hints for emitter selection
The following steps coupled with above provided information may serve as a guideline for the emitter selection process. First determine the general type of emitter that best fits the needs of the crop to be irrigated and the area to be wet, i.e., continuous wetting pattern for vegetable crops where a drip tape may be more suitable, orchard crops where on-line emitters could be used, or jets where light textured soil prevails or where light water applications with large foot print are more compatible with the crop requirements. Second, according to the required discharge, spacing, and other planning conditions, choose the specific emitter needed, i.e., which drip tape, jet pattern, or on-line emitter, could be more fitting. Third, determine the required discharge, q, and operating pressure head, H, for the average emitter that fit the system design and prevailing conditions (e.g., water quality, weather conditions). Fourth, examine the emitter characteristics described above and enquire with emitter manufacturers regarding the tolerance of emitter components to chemicals such as acid and chlorine usually used for system disinfection and cleaning. Finally, local and personal experience may need to be taken into consideration.E: Chemical Injectors
One of the advantages of microirrigation systems is to apply water-soluble chemicals through the stream of irrigation water (chmigation). That includes injecting fertilizers (fertigation), system maintenance chemicals, such as chlorine and acid products as well as herbicides, pesticides, and soil amendments such as gypsum.
A properly designed, well-managed and maintained microirrigation system provides the capability for precise and localized application of fertilizers. This makes it possible to match the amount of fertilizer applied to the needs of the plant at each stage of growth, improve crop yield, reduce the amount and cost of applied fertilizer, and cut down on nitrate leaching and pollution of groundwater.
Chemical injectors are ususally integral parts of the drip/microirrigation systems in order to implement chemigation, e.g., fertigation. Extreme care should be taken to ensure the safety for the operators and that the injection system is equipped with proper backflow prevention devices to protect the water sources (surface and underground) against any contamination with applied chemicals.
Fertilizer injection should be done during the middle third of the irrigation set to allow for uniform application of the fertilizer. This injection pattern enables washing the fertilizer out of the system by the end of the set so it will not linger in the lines and becomes a source of nutrients for microbial growth that causes system clogging.
1. Injection Devices
Metering injection units include diaphragm or piston pumps and venturi injectors. Pressure differential tanks, or batch tanks, are the least expensive but will not provide consistent flow of chemicals into the system. Injection pumps are the most expensive but the most accurate injection devices.
It is desirable to inject a total amount of fertilizer during the irrigation set time but the actual application rate may not be so important. However, the uniformity of fertilizer application (i.e., all plants receive essentially equal amount of fertilizer) is rather important and can be achieved if high drip system emission unifotmity is maintained. On the other hand, for chemical treatment of clogging, e.g., acidification and chlorination, the injector must be capable of injecting a constant dosage to maintain certain pH or free chlorine level in the water. Since most injectors are used for both fertilizer injection and clogging prevention, a constant rate injector would be desirable. Figures 45 and 46 show example of diaphragm and piston injection pumps respectively, while figure 47 illustrates the installation and connections of these pumps to the piping of the irrigation system. Figure 48 is an illustration of an installation pattern for the venturi injector.
Figure 45. Diaphragm metering pump with four independent heads,
allowing injection of four chemicals simultaneously at
different injection rates (Courtesy of Ozawa, Inc.)
Figure 46. Piston injection pump (courtesy of Inject-O-Meter)
Figure 47. Installation schematic of an injection pump connected to
the irrigation system and fertilizer tank.
Figure 48. Installation schematic of a venturi injector
(the strainer sits in the chemical solution tank).
2. Backflow Prevention
Injected fertilizers or other chemicals could contaminate the water source (e.g.,groundwater) if the irrigation water backflows into the source or if injection continues after the irrigation pump stops. The following devices should be installed to prevent such hazard:
a) On the Irrigation Pump Discharge Line
1. Check valve upstream from the chemical injection point:
to prevent back-flow of fertilizer solution into the water source when the irrigation pump stops.
2. Vacuum relief valve (A/V valve) between the check valve and the pump:
to prevent vacuum from developing in the column pipe as the water flows down the well when the pump stops. Such vacuum can induce leak around the check valve
3. Low pressure drain upstream from the check valve:
to intercept any leakage from the check valve. The capacity of the drain should be at least 10 gallons per minute.
b) On the Injection Pump
1. An interlock between the water supply pump and the chemical injection pump or intake solenoid valve:
to turn off the injection pump or shutoff fertilizer supply line if the irrigation pump unexpectedly stops while chemicals are being injected.
2. Check valve in the injection pump discharge line:
to prevent irrigation water from flowing into the injection system if the inject ion pump unexpectedly stops. The check valve should be spring loaded to prevent chemicals from flowing from the supply tank into the irrigation system by gravity if the irrigation pump unexpectedly stops.
c) Venturi Injector
1. Check valve in the intake line of the venturi injector between the fertilizer tank and the suction port of the injector:
to prevent water from flowing into the supply tank.
2. Check valve in the line connected to the outlet port of the venturi injector:
to prevent fertilizer-bearing water from flowin into the water source if the direction of water flow is reversed upon an unexpected shutoff of the irrigation pump.