Irrigation system foundation

After nozzle selection, arrangement and rotary irrigation zoning are completed, the flow of pipelines at all levels can be calculated and hydraulic calculation can be carried out. The flow rate of branch pipe is the sum of the flow rates of nozzles working at the same time on the branch pipe, and the flow rate of main pipe is the sum of the flow rates of nozzles working at the same time in the system. After the flow is determined, the pipe diameter can be selected and the head loss of the pipeline and system can be calculated. The main task of hydraulic calculation is to determine the head loss of pipeline. Calculation method of head loss in pipeline Water flowing in pipeline will produce mechanical energy loss, that is, head loss. Head loss can be divided into friction loss along the way and local resistance loss. The head loss along the way is the loss caused by the internal friction of water molecules after the water flows through a certain pipeline distance; Local head loss is the loss caused by the change of flow pattern when water flows through various fittings, valves and other equipment. The sum of the head loss along the pipeline and the local head loss is the total head loss of the pipeline. 1. 1 Calculation of head loss along the way There are many empirical formulas for calculating head loss along the way. For rigid plastic pipe (PVC), the commonly used formulas are as follows: Hf = 9.48X 104, where Hf is the head loss along the way (m); L, q and d are the length (m), flow rate (m3/h) and inner diameter (mm) of the pipeline respectively. 1.2 Calculation of local head loss The calculation formula of local head loss is: Hj =ξ, where Hj is local head loss (m); ξ is the local resistance loss coefficient, which is related to the types and sizes of pipe fittings and valves; V and g are the velocity of water in the pipeline (m/s) and the acceleration of gravity (9.8 1m/s2) respectively. For a large irrigation system, if the local head loss of each pipe fitting and valve is calculated according to the formula, the workload will be very complicated. Therefore, in the actual design work, generally, the head loss Hf along the way is calculated first, and then the local head loss Hj = 10% Hf can meet the design requirements. 2. Hydraulic calculation of branch pipe: Because there are many nozzles installed on the branch pipe, the flow in the branch pipe decreases according to a certain law, so the actual head loss along the branch pipe is far less than the value calculated according to the total flow of the branch pipe, that is, Hf actual = F × Hf formula: f is the multi-port outflow coefficient, and its value is generally between 0.3 and 0.6, which is related to the number of outlets, the position of the first outlet and the pipe material, and can be obtained by hydraulic calculation of the branch pipe. This principle is translated into the requirement of pressure, that is, the pressure at any two nozzles on the branch pipe should not exceed 20%(H set) of the nozzle design working pressure. When designing, not only the head loss should be calculated, but also the influence of topography on pressure should be considered. In practical engineering, sometimes reducing branch pipes are used to save investment, or because of the shape of the plot, the outlets are not necessarily equidistant and equal in flow, so it is necessary to calculate the branch pipe section. Hydraulic calculation of branch pipe is often an iterative process. After nozzle selection, arrangement and branch pipe length are determined, the basic flow of hydraulic calculation is: calculating branch pipe flow → preliminarily setting pipe diameter → calculating head loss → checking whether outlet pressure difference is less than or equal to 20% H setting → if it exceeds 20% H setting, repeat calculation after adjusting pipe diameter → finally determining branch pipe diameter. Generally, it is not necessary to calculate all the branch pipes in design, and the branch pipe under the most "dangerous working condition" can be selected for hydraulic calculation. In most cases, "danger" occurs in the branch pipe farthest from the head or the branch pipe with the highest terrain in the system. If the pressure of the system can meet the pressure requirements of these branches, it will naturally meet the pressure requirements of other branches. 3. Hydraulic calculation of main pipe 3. 1 Preliminary determination of pipe diameter, especially the size of main pipe has great influence on the total investment of irrigation system. Excessive pipe diameter, increased investment and unreasonable economy; The pipe diameter is too small, the head loss is large, and a large water pump is needed. The operating cost of the system is high, and the flow in the pipeline is large, which is easy to produce water hammer, which is not good for pipeline safety. The following empirical formula can be used for the preliminary estimation of the main pipe diameter: d =11(q <120m3/h), where: d is the pipe diameter (mm); Q is the flow (m3/h). Or use the formula of economic velocity method: D = 1. 13, where d is the pipe diameter (mm); Q is the flow (m3/s); V is the economic flow, and it is generally taken as V≤3m/s according to experience. 3.2 Hydraulic calculation of the main pipe The hydraulic calculation of the main pipe is simpler than that of the branch pipe, and the head loss can be calculated according to the pipe diameter, flow rate and length of different pipe sections. The general requirement is that the pressure along the branch pipes of the main pipe should meet the pressure requirements at the entrance of each branch pipe. (IV) Selection of water pump The main task of water pump selection is to determine the flow and lift of the water pump. After the above steps are completed, the flow and lift can be calculated. Pump flow: q = σ n nozzle q pump head: H = H+σ HF+σ HJ δ where: N nozzle is the number of nozzles working at the same time; Q is the single nozzle flow; H is the design working pressure of the nozzle (m); σ HF is the sum (m) of the head loss along the pipeline between the water pump and the typical nozzle. The so-called typical nozzle generally refers to the nozzle farthest from the pumping station or with the highest position. σ HJ is the sum of the local head loss (m) between the pump and the typical sprinkler, including the local head loss of valves, filtering equipment and fertilization equipment; δ is the height difference (m) between the typical sprinkler and the water level of the source water or the dynamic water level in the well. When selecting the pump model, you can refer to the product catalogue of the relevant pump manufacturer. The actual flow and lift of the selected pump should generally be slightly larger than the above calculated values to ensure that the design requirements are met. For an irrigation system with urban water supply network as its water source, it is not necessary to choose a water pump, but to check whether the pressure provided by the water supply network can meet the pressure required by the irrigation system (that is, the lift value calculated above). If it is not satisfied, it is generally necessary to increase the pipe diameter at all levels to reduce the head loss; Or choose a sprinkler with good low pressure performance, so that the pressure required by the irrigation system is less than or equal to the pressure of the urban water supply network. V. Construction and Installation of Sprinkler Irrigation System The general requirement for the construction and installation of sprinkler irrigation system is to be carried out in strict accordance with the design. Modification of the design must be approved by the design unit and approved by the competent department. When it comes to the construction of related buildings, it should meet the requirements of current codes, such as Code for Construction and Acceptance of Water Supply and Drainage Buildings and Code for Construction and Acceptance of Underground Waterproofing Works. According to the characteristics of lawn sprinkler irrigation system, the following problems should be paid attention to in its construction and installation: (1) In the construction of existing lawn plots, in addition to protecting the existing lawn as much as possible, special attention should be paid to the treatment of ditch waste soil. Abandoned soil should be placed in layers, and buried pipes should be backfilled in layers in reverse order to ensure that the soil in the planting layer along the pipeline is consistent with the original soil. (2) Drainage devices should be installed on the main pipe and each branch pipe, which is convenient for flushing pipes and preventing freezing in winter. Even in the south where there is no frost damage, in the non-irrigation season, it is generally necessary to empty the pipeline to prevent water from staying in the pipeline for too long to produce microorganisms and attaching to the pipe wall and nozzle, which will affect the sprinkler irrigation effect. In addition to the common gate valves and ball valves, there is also an automatic drain valve, which can automatically drain the water in the pipeline after irrigation stops. (3) When the system pressure changes or the terrain fluctuates greatly, pressure regulating equipment, such as PRS-B pressure regulator produced by Rain Bird Company and matched with solenoid valve, should be installed at the valve of branch pipe to balance the pressure at the inlet of branch pipe and ensure the spraying uniformity of the system. In addition, inlet and outlet valves and pressure relief valves should be installed in necessary pipe sections to protect the safety of the system. (4) In order to facilitate temporary water intake or artificial irrigation in corner areas where sprinkler irrigation is difficult to control, it is generally required to install a certain number of quick inlet valves (convenience bodies) on the main pipeline, such as Rain Bird P33 quick inlet valve. This quick water inlet valve is used in conjunction with the matching key. When the key is inserted, the valve can automatically open the water supply. To stop irrigation, just pull out the key and the valve will automatically close. (5) Install the buried lawn sprinkler 1. Sprinklers must be preset before installation. Most nozzles with adjustable spray fan angle are set to 180 degrees when they leave the factory, so the nozzles should be adjusted to the required angle according to the actual terrain requirements for spray fan angle before installation. In addition, some sprinklers, such as Rainbird R-50, should also set up the slogan that the filter screen enters the water, which is consistent with the label of the sprinkler. 2, the top of the nozzle should be flush with the final ground. This requires that when installing sprinklers, the top of sprinklers should be lower than the scarifying ground, leaving room for future ground settlement; Or install sprinklers when the lawn floor no longer sinks. 3. For the connection between nozzle and branch pipe, it is best to use rotary joint, also known as Qian Qiu frame. It can effectively prevent the damage of pipes and nozzles caused by mechanical impact such as lawn mower operation or human activities. At the same time, the hinged joint is adopted to facilitate the adjustment of the installation height of the nozzle during construction. 4. In areas that are inconvenient to manage, anti-theft accessories supporting the nozzle can be installed to prevent the nozzle from being lost. For example, the special anti-theft connector of the rain bird PVRA nozzle is installed at the entrance of the nozzle. When someone tries to unscrew the nozzle, the joint rotates with the nozzle and cannot be unscrewed. Only when the lawn is dug up can the connector and sprinkler be removed with tools. Automatic control of lawn irrigation system with the development of economy, the requirements for lawn greening engineering level are getting higher and higher. At the same time, in order to further solve the problems of water and energy shortage and the increase of labor cost, more and more lawn greening projects adopt automatic control irrigation systems. At present, the commonly used automatic control systems can be divided into two categories: sequential control irrigation system and central computer control irrigation system. Timing control irrigation system Timing control irrigation system takes irrigation start time, irrigation duration and irrigation cycle as control parameters to realize automatic irrigation of the whole system. Its basic components include: controller, solenoid valve, and optional equipment such as soil humidity sensor, rainfall sensor and frost sensor. Controller is the core of the system. Irrigation managers can set irrigation start time, irrigation duration, irrigation cycle, etc. into the program of the controller, and the controller not only sends signals to the solenoid valve through cables to turn on or off the irrigation system. There are many kinds of controllers, which can be divided into electromechanical hybrid circuit, AC power supply and DC battery operation. Its capacity is large and small. The smallest controller only controls a single solenoid valve, and the largest controller can control hundreds of solenoid valves. The solenoid valve is usually an AC 24 volt diaphragm valve, which is connected to the controller through a cable. The electromagnetic valve switch has a certain delay, which can effectively prevent the water hammer phenomenon in the pipe network and protect the system safety. At present, the automatic control irrigation systems in China are basically sequential control irrigation systems. The central computer controls the irrigation system. The central computer controls the irrigation system and feeds back meteorological parameters (temperature, relative humidity, rainfall, radiation, wind speed, etc.). ) send the information about plant water requirement to the central computer through the automatic electronic weather station. The computer will automatically determine the amount of irrigation needed on that day, and inform the relevant execution equipment to turn on or off the sub-irrigation system. In the central computer-controlled irrigation system, the above-mentioned sequential control irrigation system can be used as a subsystem. MAXICOM2 central computer-controlled irrigation system developed by American Rain Bird Company can remotely control an unlimited number of subsystems by computers through wired, wireless, optical cables and telephone lines. For example, all garden irrigation systems as small as a park, as large as a city or even several cities can be automatically controlled by a central computer. This central computer-controlled irrigation system is an automatic irrigation system in the true sense. At present, it has been widely used in the irrigation system of garden green space and golf course in many developed countries. Seven, lawn water management Water management is the core of all management work of lawn sprinkler irrigation system. After the lawn sprinkler irrigation system is completed, the quality of water management is directly related to whether the sprinkler irrigation system can play its due role. The basic task of water management is to organize lawn sprinkler irrigation reasonably according to the planning and design of sprinkler irrigation system and local climate, lawn type, growth stage, soil moisture and water supply, improve irrigation efficiency and maintain the best growth state of lawn. Its specific content includes the following aspects. (1) Formulation of irrigation scheme The design of sprinkler irrigation system is generally aimed at the most unfavorable conditions and can meet the maximum water demand of lawn. When the system is running, the irrigation scheme should be determined according to the actual situation, including irrigation time, irrigation duration and irrigation cycle. 1, irrigation time irrigation season, most of the day can be irrigated. However, irrigation at noon should be avoided in hot summer to avoid scalding the lawn, and at this time, evaporation is the largest and water utilization rate is low. Irrigation at night can avoid the above situation, but people are often worried that lawn leaves will be wet for too long, which will easily lead to diseases. This disadvantage of night irrigation can be solved by applying fungicides. Irrigation in the morning, sunshine and morning wind can make the leaves dry quickly, which is an ideal irrigation time. However, for non-automatic sprinkler irrigation system, night irrigation and early morning irrigation will bring some inconvenience to operators, so night irrigation is also a better choice. Irrigation time is also limited by human activities. For example, golf courses are basically watered at night, so that the lawn will not affect players' playing during the day; The lawn of the football field should be watered the day before the game to reduce the damage to the field and the influence on the athletes' performance. 2. Irrigation duration The irrigation duration mainly depends on the combined sprinkler irrigation intensity of the system and the water holding capacity of the soil, that is, the field water holding capacity. When the intensity of sprinkler irrigation is greater than that of soil infiltration, stagnant water or runoff will be generated, and water cannot fully penetrate into the soil; If the irrigation time is too long, the irrigation amount will exceed the field capacity of the soil, resulting in deep leakage and loss of water and nutrients. Therefore, the general rule is that the infiltration intensity of sandy soil is high and the field water capacity is low, so the duration of one irrigation is short, but the irrigation times are many and the interval time is short, that is, the amount of irrigation needed is small; On the contrary, for high-viscosity soil, the duration of one irrigation is long, but the irrigation times are few. Soil moisture measuring instrument can determine irrigation time more scientifically. At present, the commonly used instruments in engineering include electronic soil moisture analyzer and tensiometer. 3. Irrigation cycle Irrigation cycle, that is, irrigation interval or irrigation frequency, is not only related to the soil properties mentioned above, but also mainly depends on the lawn itself. Too frequent irrigation will make the lawn have high morbidity, shallow root layer, poor trampling resistance and poor growth; However, if the irrigation interval is too long, the normal growth of lawn will be inhibited due to lack of water, which will affect the quality of lawn. The irrigation plan is not fixed, and it should be made in units of ten days or months according to different seasons, but it should be adjusted at any time with reference to the actual irrigation effect and natural rainfall. (2) Establish system operation files. The operation of sprinkler irrigation system, including start-up time, irrigation duration, water consumption and electricity consumption, should be recorded and archived in detail, and these data should be analyzed in time to provide basis for further improving management and monitoring system operation. (III) Evaluation of Irrigation Effect After the sprinkler irrigation system is put into use, it can intuitively evaluate the lawn growth, green period extension, water saving and labor saving. It is also possible to evaluate the uniformity of sprinkler irrigation system and the utilization rate of irrigation water through practical tests, and to correct the irrigation plan in time, which will provide reference for improving the planning and design level of sprinkler irrigation system in the future.