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I Water Saving Irrigation Design i Knowledge Lecture bookmark0 This Lecture i National Spraying Technology Letter Ibookmark1 I Low-pressure Pipeline Water Transmission Equipment bookmark2 Topic Overview An engineering form of water irrigation. According to the working pressure of the pipeline system, the pipeline water can be divided into two types. One is a medium and low pressure pipe network system with a working pressure of 41.0MPa. The system has many pipeline stages and a large control area, and the field irrigation method is mostly sprinkler irrigation. The other is a low-pressure pipeline system whose working pressure generally does not exceed 0.2 MPa, and the outlet pressure of the furthest part of the pipeline is controlled at 0.002 to 0.003 MPa. The system has fewer pipeline stages and can be directly sourced from water sources such as machine wells and pump stations. Water is taken, or it is matched with the open-drain in large and medium-sized irrigation districts. The bucket canal is changed to pipeline water delivery. Generally, ground irrigation methods such as ditch and border irrigation are still used in the field.
As a kind of advanced water delivery method, low-pressure pipeline water transportation plays an important role in the development of water-saving irrigation in farmland. Its main advantages: basically there is no leakage and evaporation loss, and the water transfer efficiency is more than 95%; due to the fast water transfer and time saving, the irrigation operation efficiency is improved; because the open channel occupation is reduced, the land utilization rate is improved, It also facilitates the field operations of agricultural machinery and promotes agricultural modernization; in addition, the construction, maintenance, and use techniques are simple, easy for farmers to master, and the investment is not high. Therefore, with the support of the government, farmers are easy to accept, and its application prospects are broad. In recent decades, China has conducted in-depth research and experiments on low-pressure pipeline water delivery, and has demonstrated and promoted on this basis. Therefore, as of the end of 1997, the area of ​​farmland irrigated with low-pressure pipelines has reached 5.27 million hm2. In addition to the large-scale promotion and application in well irrigation areas, there are also in canal irrigation areas, southern river network irrigation irrigation areas and hilly areas. Certain development. At present, the application has covered 25 provinces, cities and autonomous regions across the country.
1. The composition and classification of the pressure change pipeline water conveyance system The composition of the low pressure pipeline water conveyance system is based on the functions undertaken by the various departments. The low pressure pipeline water conveyance system consists of water source and water intake engineering, water conveyance system, water supply and distribution device, safety protection equipment, field irrigation The facilities are composed as shown.
Water source and water intake project The low-pressure pipeline water supply system includes wells, rivers, canals, reservoirs, ponds, etc. The water quality should meet the irrigation water standards for farmland. In order to draw water from well irrigation area, it is necessary to select a suitable pump and install a pressure gauge and a water meter. In addition to the need for water intake gates and water measuring buildings, water intakes in gravity-fed irrigation areas or large and medium-sized water-lift irrigation areas are also required to be equipped with trash racks and sedimentation tanks.
The water system is composed of water pipelines and pipe fittings (tees, tees, elbows, reducing joints, etc.).
Water pipelines can be divided into plastic pipes, prefabricated cement pipes, concrete pipes cast on site, etc. according to pipe materials.
Water supply device Water supply device is a general term for connecting tee, riser, and water supply plug (or water outlet). Generally speaking, the water supply device generally refers to the water supply hydrant (or water outlet). The water outlet refers to the water outlet that leads the water of the underground pipeline system out of the ground for irrigation, and generally does not move the pipe to the ground plane. The water supply plug is a control device that provides a source of pressure water to the ground pipeline, and is a water outlet connected to the ground mobile pipe.
Safety protection device The safety protection device of the low-pressure pipeline water conveyance system mainly includes an inlet (exhaust) air valve, a safety valve, a pressure regulating device, etc.
The measuring devices mainly include measuring pressure and measuring flow devices. The pressure measurement device is used to measure the water flow pressure of the pipeline system and to understand the working pressure of the pipeline. The flow measurement device is used to measure the total flow of the pipeline and the amount of water per unit time, which is the basis of water management.
Field irrigation facilities generally refer to ground mobile pipes in semi-fixed or mobile low-pressure pipeline water delivery irrigation systems.
2. The classification of the low-pressure pipeline water delivery system is based on the fixed method. The low-pressure pipeline water delivery system can be divided into three types: mobile, semi-fixed and fixed.
The mobile finger transmission and water distribution pipelines can be moved, and both water distribution and water distribution in the field.
Most of the pipelines use hoses, which are simple and easy to operate, and the one-time investment is low. They are mostly used in temporary drought resistance in well irrigation areas. However, the labor intensity is high and the pipeline is easily damaged.
Semi-fixed means that the water pipeline is buried underground and the water distribution pipeline moves on the ground.
The pipeline system investment is higher than the mobile type, but the labor intensity is low, the operation and management are more convenient, and this form is commonly used in regions with moderate economic conditions.
The fixed type water distribution and distribution pipelines are all buried and fixed, and the irrigation water is directly fed into the furrow or ditch through the outlet. Due to the high density of fixed pipes and large one-time investment, the operation and management are convenient and the irrigation is even. This form can be adopted in areas with good economic conditions.
Second, the low-pressure pipeline water conveyance equipment The pump used in the low-pressure pipeline water conveyance irrigation system mainly uses the centrifugal pump and the well in the vane pump. Centrifugal pumps include single-stage single-suction centrifugal pumps and single-stage double-suction centrifugal pumps. Well pumps mainly include long shaft deep well pumps (such as D type,! Type, C type, etc.) and deep well submersible electric pumps (such as Q type, Q type, NQ type, etc.).
When choosing a pump, we must first consider the form of the water source. Centrifugal pumps can be selected for water sources with shallow water depth and little change. For shallow wells with large water depths and centrifugal scoops cannot be used, if the head is not large, single-stage submersible electric pumps can be selected. For small flows, single-phase motor submersible pumps can be considered. For water sources with large water depth and large head (such as deep wells), multi-stage submersible pumps (such as Q series pumps) or long-axis deep well pumps (such as C series pumps) can be used.
The pipeline is an important part of the low-pressure pipeline water delivery irrigation system. It is connected to the engineering quality M and the cost of the F low-pressure pipeline. The pipelines include cement prefabricated pipes, concrete pipes and plastic pipes poured on site. Easy to handle, smooth inner wall, low water resistance, corrosion resistance, and easy installation, so it has been widely used in low pressure pipeline water delivery system in well irrigation area. As of the end of 1995, the area of ​​irrigation project with plastic pipe as low pressure water delivery pipe has exceeded the low pressure water delivery More than 50% of the total area of ​​the irrigation project is up to 80% in Shandong Province. In the canal irrigation area and the southern river network irrigation irrigation area, due to the large water flow in the pipeline, large-caliber cement prefabricated pipes are generally used, and light-weight large-caliber plastic coils There are also pilot applications for winding spiral pipes. The materials of plastic pipes for low-pressure water delivery are mainly polyvinyl chloride (PVC) and polyethylene (PE). Both single-wall and double-wall corrugated structures are dedicated to low-pressure water delivery irrigation The product specifications of the thin-walled rigid polyvinyl chloride (PVC-U) pipes are shown in the national standard GB / T 13664-92, and the performance indicators are shown in Table L. Table 2 is the production of high-density polyethylene pipes that can be used for low-pressure water delivery Performance index, which is the national standard specifications, see GB / T13663 -92. May be used for the low pressure water double wall corrugated plastic pipe see its structure.
Table 1 Performance indicators of thin-walled PVC-U pipes Item indicators Longitudinal retraction rate, Raspberry 5 tensile yield stress, MPa 40 Hydraulic test (20 feet, 4 times working pressure, 丨 h) No rupture, no leakage drop hammer impact ( 0X) Non-rupture stiffness (at 5% deformation), MPa flat test (compressed to 50%) without rupture Table 2 HDPE pipe performance indicators Project indicators Tensile yield stress, MPa longitudinal size shrinkage rate, at 3 Hydraulic temperature: 20 Time: 1h Circumferential stress: 11.8 MPa without rupture and leakage. Circumferential force: 3.9 MPa without rupture and leakage test. In order to meet the demand for large-diameter low-pressure water transmission pipes in the canal irrigation area, large plastic spiral coiled pipes have been in the field of low-pressure water transmission A pilot application was carried out. The large plastic coiled spiral tube is made of plate and strip material with T-shaped ribs, which is rolled on a tube rolling machine. The plates are locked by a self-locking mechanism that is quickly fitted. Generally speaking, the self-locking mechanism is bonded with an adhesive or welded with melted polyethylene. The diameter of the winding tube is 150 ~ 2600 f. The winding tube is generally used to discharge sewage without pressure. Therefore, when it is used in low pressure, it is necessary to select the throat of the plate and strip material. The large-diameter double-wall spiral plastic pipe developed by Shenyang Plastic Machinery Research Institute and China Academy of Water Resources and Hydropower Research has a cross-section of 400 mm. Its failure internal pressure can reach 0.63 MPa. Pilot application of cement prefabricated pipes has been conducted in Yehe Irrigation District of Hebei Province. Due to economic constraints, some cement prefabricated pipes are still being used in well irrigation districts. See Table 3 for their varieties and properties. The length of the pipe is mostly 1000mm. Table 3 Varieties and performance of prefabricated cement pipes Pipe name Inner diameter Wall thickness Inner water burst pressure MPa Impermeability pressure MPa Cement sand soil pipe Cement sand pipe Cement soil pipe Cement stone chip pipe Cement furnace flooded pipe Thin wall concrete pipe in The large-caliber cement prefabricated pipes used in canal irrigation areas and southern river network irrigation irrigation areas include plain concrete pipes, reinforced concrete pipes, and cement stone pipes. The diameter of the pipe is 300, 400, 500mm, etc., the pipe length is 1 000-2000mm, the internal water breaking pressure is for the concrete pipe cast on site. This kind of pipe material should be constructed with a secondary or primary forming machine for continuous casting on site, and the integrity is good. , The construction speed is fast. The secondary forming is because the upper and lower half pipes are cast separately, the two sets of tools are constructed, and the procedure is complicated. Therefore, a primary forming machine that uses advance, feed, vibration, and forming is ideal. It is the structure diagram of WD-1B one-time forming tube making machine. The inner diameter of the tube is 100, 150, 200, 250, 300mm, etc., the burst pressure of the internal water is 0. 1. Wiper 2. Wiper hopper 3. Counterweight box 4. Gradient section 5. Upper hopper 6 . Vibrator 7. Lower hopper 8. Machine head 9. Traction ring 10. Lower vibrator 11. Slide water supply device is divided into three types of mobile, semi-fixed and fixed according to the structure.
(U mobile water supply plug consists of upper and lower plug body, its characteristics: â‘ The water sealing part is in the lower plug body, the lower plug body is fixed on the riser of the underground pipeline, and is equipped with a protective cover. The water tap can be opened and closed without stopping the machine to replace the irrigation point. â‘¢The upper plug body is moved and used. The same pipeline system only needs to be equipped with two or three upper plug bodies, which saves investment. Its function is to control the direction of the water supply outlet. There are various types such as NS, NSQ and DGS series (KNS series water supply plug local resistance coefficient is 1.50-2.02, NSQ series water supply plug local resistance coefficient is 1.60-2.45, DGS series water supply plug local resistance coefficient is 1.5 ~ 2.0. Water supply hydrant (2> Semi-fixed water supply hydrant Under normal circumstances, it integrates water sealing and water supply control. The plug body is connected to the riser or flange connection. It can be removed indoors during the non-irrigation period. Generally common See the lever valve type water supply plug, screw gland type water supply plug, etc.
The local resistance coefficient of the midge valve valve type water supply plug is 1.595, and the local resistance coefficient of the screw gland type water supply plug is 1.0-1.8. The surrounding 6 semi-fixed water supply pin valve type water supply plug (b> screw gland type water supply plug 1 . Rod 2. Packing gland 3. Top cover 1. Operating rod 2. Bolt shell 3. Water stop valve valve 5. Bolt shell 4. Sealing rubber pad 5. Flange pipe (3) The fixed water supply device is characterized by It integrates water sealing and water supply control. The plug body is generally firmly connected to the underground pipeline system through the riser and cannot be disassembled. Such as the silk-covered concrete outlet, the above-ground concrete water supply plug, etc. (>. Low-pressure pipeline water delivery The safety protection devices of the irrigation system include inlet (exhaust) valves, safety valves, pressure regulating devices, check valves, and drain valves, etc. Its main functions are: overpressure protection; damage to the vacuum of the pipeline; elimination of air in the pipe and reduction of water resistance ; Prevent the pipeline from returning water; drain the water stored in the pipeline in winter, prevent the pipeline system from being damaged due to frost heave, etc. To use more inlet (exhaust) air valves and safety valves on the low-pressure water pipeline.
The pressure measuring devices commonly used in low-pressure water pipeline systems are mainly spring tube pressure gauges. Its external dimensions, specifications and performance can be obtained from the hardware manual.
In order to realize the planned water consumption, collect water fees according to the quantity, and promote water saving, it is necessary to install flow measurement devices, such as water meters, flow meters, and flow meters in the low-pressure water pipeline system, among which water meters are the most commonly used. China currently does not have a dedicated agricultural water meter, so industrial and civil water meters are often used, such as the LXS rotor-wet water meter and the LXL horizontal screw-type water meter. When selecting a water meter, it should be selected according to the flow rate of the pipeline and the head loss curve of the flow meter provided by the manufacturer. As far as possible, the flow rate of the water meter is often close to the nominal flow.
Field irrigation facilities refer to ground mobile pipes in semi-fixed or mobile low-pressure water delivery pipeline systems. Mobile pipes are usually light, soft and easy to coil, such as LLDPE plastic hoses, plastic coated hoses, etc. In recent years, a new type of ground mobile sluice irrigation system has been successfully developed by the China Institute of Water Resources and Hydropower Research on the basis of introducing foreign advanced technical equipment. The sluice pipe irrigation system consists of a water delivery hose and a water distribution port with adjustable opening. The water conveying hose is made of polyethylene mixed with ultraviolet shielding agent and color masterbatch, and the available folding diameter is 160 15-0.30mm. The water distribution port is composed of 4 parts: gate, pressure ring, gate window and gate , Produced with engineering plastics.
Teacher, expert who enjoys special government allowance, has long been engaged in water-saving irrigation technology, equipment research and development, standard formulation and promotion and application.
Editor in charge: Han Jianxin bookmark7
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