First, the structure of submersible pump Submersible pump is the pump and motor closely integrated into one common diving operation of the unit. Usually based on the relative position of the pump and the motor can be divided into submersible pump on the pump and pump the two main structures. 1 on pump submersible pump on pump submersible pump structure pump on top, the motor below. This structure is conducive to reducing the radial size of the pump, it is mostly used in well submersible pumps and small submersible pump. In the pump submersible pump structure, usually using wet submersible motor. Motor cavity filled with water, transformer oil or spindle oil, the stator coil with reinforced insulation oil, water resistant enameled wire wound. Fixed rotor immersed in liquid operation, the motor outside was flooded, cooling conditions are good. Wet motor bearings can be used plastic bearings or rolling bearings. The shaft extension and bearing seal with a skeleton oil seal or mechanical seal, the seal only from sediment and dirty water, the structure is simple. Wet submersible pump more thoroughly solve the electromagnetic part and the bearing part of the sealing problem, promote the application earlier. However, the water friction loss of the stator and stator in the wet motor is larger, which is proportional to the fifth power of the rotor outer diameter. So usually made of slender type to reduce friction loss, improve motor efficiency. 2 Pump submersible pump Pump located below the motor called pump submersible pump, usually it can be divided into two types of built-in and external. Built-in pump submersible pump delivers the liquid first through the motor surrounded by the annular flow, so that the cooling motor and then out of the pump pressure outlet. This pump even in the case of drained suction sump, but also do not have to worry about motor heating, so the scope of application is expanding. The submersible pump submersible pump discharges liquid directly from the pressure chamber behind the impeller or at the outlet of the guide vane. The motor is also cooled by the pumped liquid. As the pump structure can work in the lighter liquid, it is often used in submersible electric pump, especially it is the main structure of large-diameter submersible pump. For sub-pump submersible pump, because it can be used in the process of mass production of ordinary dry three-phase asynchronous motor, the seal on the reverse motor housing mating surface with "O" rubber seal closed, the output The shaft extends from the lower end. The shaft extension is provided with a mechanical seal rotating in the sealing liquid, usually one to three single-end or double-end mechanical seals to strictly prevent the transported liquid from entering the motor cavity along the shaft. In the early days have also used a gasketed seal structure, the lower end of the motor has a gas sealed chamber, which is connected to the outside world by several channels, the pump sneaked into the suction liquid pool, the air inside the sealed chamber formed under the action of liquid pressure outside the body Air cushion to prevent liquid from entering the motor cavity. Under the pump submersible pump mechanical seal is located in the outlet flow high pressure zone, the higher the head, here the higher the water pressure, so the mechanical seal performance by the lift control. Second, the submersible pump seal and protection technology The development of submersible pump basically depends on the sealing technology research results. The submersible pump seal has always been the focus of the majority of users are concerned about the potential of water always feel insecure, do not worry, because most of the dry motor, in case of leakage how to do? Therefore, if the submersible pump to conventional Motor as safe and reliable, then the promotion is no problem. Submersible pump seal is usually divided into two parts, electrical seal and bearing seal. In the wet submersible motor, the two parts of the seal to solve the more successful, many submersible pump plant in China to produce a single wet submersible motor pump section, such as Anqing Motor Factory, Taizhou submersible pump plant. Wet submersible motor electrical seal and bearing seals are independent of each other, such as bearing seal failure, only cause water lubrication Bearing water into the sand, grease or thin oil lubrication of the rolling bearing water, the consequences of accelerated wear and corrosion, as long as the motor is not short circuit as usual Can run. Therefore, as long as the user in accordance with the maintenance schedule promptly replace the wearing parts and lubricants, we can ensure long-term operation of wet submersible pump. For submersible pumps using dry motors, the mechanical seals on the shaft, in addition to sealing the bearings under the motor (oil chamber), also serve to seal the motor cavity to strictly prevent liquid being transported from entering the interior of the motor. Currently, the materials and construction of mechanical seals have been greatly developed, typically with one to three single-ended or double-ended mechanical seals between the motor and the unfavorable components. The upper layer is usually graphite / tungsten carbide, the lower layer is tungsten carbide / tungsten carbide. In addition, the sealing material in addition to tungsten carbide, silicon carbide, aluminum oxide or other cemented carbide may also be used. In addition, the submersible pump can be attached to the multi-layer protection devices, such as built-in stator windings thermal overload protector to prevent the motor overload and fever. Set in the wiring cavity leak detection probe, when the cable breaks or other causes of leakage, the probe sends a signal, the control system to pump protection. Leakage catchment is installed on the lower bearing of the dry motor, and a leak detector --- float switch is installed in the tank to automatically alarm if the liquid leaking into the tank reaches a certain amount. In the mechanical seal end of the oil chamber also has electrode protection, when the water leaks into the oil chamber when the electrode signals that the control system. At this point, the management promptly maintained, the mechanical seal inspection and replacement, the trough and oil chamber liquid poured out, and the oil chamber and then add a new mechanical oil, and then tighten the bolt can be. The entire maintenance process is simple and convenient, the pump can be put into work immediately. Submersible pump seal In addition to taking the above measures, it is still further study how to improve its sealing reliability and safety. For example, a high-power dry-type motor is additionally provided with an automatic air-inflating device which is externally energized to the inner cavity of the motor to make the inside of the motor be in a positive pressure state and equalize or exceed the water pressure outside the sealed body so as to enhance the effect of stop-leak. There are also mechanical seals on the pump section to take decompression measures, such as the creation of pressure relief holes or increase the water thrower, in order to reduce the water pressure and sand control. There are additional impeller in the pump behind the impeller to reduce the mechanical seal at the pressure and protect the shaft seal. The choice of mechanical seal should also pay attention to a reasonable structure, good sealing performance, installation process is simple and convenient. In short, submersible pump seal technology problems are well resolved, submersible pump will have a broader market. Third, the submersible pump control system As the submersible pump is dive into the underwater work, its control system is particularly important. Therefore, when designing the various functions of a submersible pump, one should also consider its control system. This article briefly introduces the commonly used submersible pump control system abroad. 1 water level control system Water level control system usually has four forms, as shown in Figure 1. In the pumping station, in most cases should choose the float water level regulator. In the regulator with a switch, used to adjust the water level with the tilt or vertical operation. For one pump, two water level regulators are used for start-up and shut-down, while for standby pumps the water level can be set by additional regulators. In construction sites, mines and pumping the media with the risk of explosion and other occasions, optional remote control device. It is mounted on the control panel to measure the motor current. It also measures run times and determines downtime, only for controlling the operation of a single pump. Figure 1 water level control system When the flow is large and requires low lift, commonly used electrodes for water level control, such as soil improvement and drainage occasions. In addition, the electrode is used to control the water level in small sump or flow-disturbing pump stations. It requires only a small space and is installed in a pipe with a diameter of 50 mm. The height of the water level is easy to control. Bubble control is a reliable way of regulating the water level in pumping stations that pump surface water, ie, small sumps and turbulent flow, which can be used with all types of pumps and with all media. This method of control, with moving parts in water, eliminates the problem of jamming or sticking, requiring only one plastic hose to be inserted into the media. 2 Combination of water level and pump control system Combination of water level and pump control system usually has four forms, as shown in Figure 2. APC Automatic Conditioning Pump Control System is a water level control system for dual pumping stations. It is a practical and economical way to control pump operation and adjust sump level. The system's control unit is a microprocessing machine that can be easily installed on the control panel of a pumping station to detect the current consumption of the submersible pump motor without the need to directly detect the water level in the sump. The system also eliminates the need for water level control facilities to protect the pump station clean. At the same time it also has the function of pumping the pump run, in order to obtain the pump wear leveling and maintain the economic operation of the interval time. In addition to the above-mentioned water level control functions, the main APC automatic control pump with mixing valve also has a very amazing effect of cleaning the pump pit. Mixing valve can be installed on all the sewage pump body, when the pump starts to form a strong stirring effect, so that the mud and covering materials are stirred into a suspension and pumped away. The PPC Piezo Pump Control System is a pressure sensing control system that is a practical and economical way to control the operation of a dual pump station and to regulate the water level. The control system consists of a sensor and a water level control device, the sensor placed in the suction tank to detect the pressure. At the same time, the system also has the function of switching the pump run during each operating cycle. The PPC piezo pump control system with agitator valve, at the beginning of each working cycle, uses the agitator valve to turn the water in the sump to prevent the floating solids from settling, which will greatly improve the working environment within the pump station. Practice shows that this PPC piezoelectric pump control system with mixing valve can greatly reduce the pumping dredging workload or no dredging at all. 3 pump start and stop control In addition, pump start and stop process is also equipped with a control system, such as 1 to 6 pumps stop and start the water level control, 1 ~ 2 pump delay start and stop control , 2 ~ 6 pumps of different start-up and shut-down water level control and 2 to 3 pumps in series operation control. Fourth, the prospect of submersible pump As the submersible pump itself and the selection of submersible pump pumping station has many advantages, therefore, China's demand will continue to grow in the future, and the following major trends. 1 large and medium-sized submersible pump to develop large and medium-sized submersible pump with simplified pump structure and save pump construction investment outstanding advantages, generally can reduce the cost of 40% to 60%, shorten the construction period 1/2 ~ 2/3. Therefore, it will be more and more widely used in municipal, mining, environmental protection and industrial and agricultural drainage. Expected future demand will be greater. 2 Development of multi-purpose multi-purpose submersible pump Submersible pump in China in the form and well-known submersible pump manufacturers compared to the product is not enough, such as with a cutting device pump, multi-stage pump, pumping corrosive diving media Electric pumps and other production is still small, but its market demand is very large, therefore, has a good development. 3 Development of high reliability mechanical seal Mechanical seal is a key part of the submersible pump, the use of two single-end mechanical seal, so that the medium pressure can be applied to the end face, the direction of leakage for the inflow of these are beneficial, but the structure slightly complex. In the oil chamber with double-ended mechanical seal, the two sides of the end face should be of different types of structure, so that the medium pressure can be applied to the lower end of the surface, otherwise only by spring force, seal the end face of the thrust easy to open the end. Therefore, further research should be conducted on the structure and materials to improve their reliability and longevity. 4 new materials, new technologies and new processes will be gradually applied ordinary pumps have been used stainless steel, Fluoroplastics (F46), lining plastic, rubber lining, spraying ceramics, all of these materials should be applied to the submersible pump as soon as possible to expand the submersible pump applications field. The application of new technologies such as computer-aided design, auxiliary manufacturing and auxiliary testing is also imperative. Facts have proved that the application of new technologies, new materials and new technologies not only liberates labor productivity, but also ensures that product quality is stable and reliable. 5 Note submersible pump appearance and gradually enter the international market China's submersible pump in the international market has obvious price competitive advantage, but must pay attention to improve the reliability and life of the pump, in particular, to improve the submersible pump The appearance of quality, to give users a kind of beauty, so that the domestic submersible pump more and more into the international market. References [1] off every edited, "Modern Pump Technology Manual," Beijing: Aerospace Press, 1995. [2] Shi Weidong, Guan Xing, "foreign submersible pump control system overview", "Journal of Agricultural Machinery", 1996 (4). [3] Qiu Chuanxin et al., "Let submersible pumps go from the deep well to the great rivers." Pumping Station Technology, 1995, (2): 4-7. [4] Yuan Shouqi, "History and development trend of small submersible pump", "Irrigation and drainage machinery", 1994 (1): 3 ~ 10. [5] Shi Weidong edited, "Fluid Machinery", Chengdu: Southwest Jiao Tong University Press, 1996. [6] Zhu Xinghua, "Large-diameter flow-type submersible electric pump structure and installation type", "pumping station technology", 1995 (2): 8 ~ 15. â–³ Author Correspondence: 212013 Jiangsu University of Science and Technology, Zhenjiang, Jiangsu Tel: (0511) 8780281