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First, the diaphragm pump Overview: diaphragm pump by the implementing agencies and valves. The use of compressed air as the power source, for a variety of corrosive liquids, with particles of liquid, high viscosity, volatile, flammable, highly toxic liquid can be smoked exhausted. Suitable for placement in a variety of special occasions, used to pump the kind of conventional pump can not suction medium. Diaphragm pump actuator with pneumatic actuators and electric actuators, models QBY-type pneumatic diaphragm pump and DBY-type electric diaphragm pump. Diaphragm pump body (body) material has four kinds: plastic, aluminum, cast iron, stainless steel, respectively, according to the requirements of liquid or gas medium selection. Membrane diaphragm inside the diaphragm is also based on different liquid media were nitrile rubber, neoprene, Viton, polyvinylidene fluoride, polyhexachlorethylene, so when ordering to specify the type of media. Second, the specific selection of diaphragm pump: 1, the role of the diaphragm pump diaphragm pump function only in the choice of pneumatic actuator only when the role of the positive and negative effect through the implementing agencies and the positive and negative valve action combination . There are four types of combination that is positive (air-off type), positive and negative (air-type), anyway (air-type), anti-anti (anti-off type) Open and Qi off two. For the choice of diaphragm pump mode of action, mainly from three aspects: (1) process safety; (2) the characteristics of the media; (3) to ensure product quality, economic loss is minimal. 2, the choice of flow characteristics of diaphragm pumps Diaphragm flow characteristics of the pump is the medium flow through the valve relative displacement and displacement (relative valve opening) relationship between the ideal flow characteristics are straight, equal percentage (logarithm), parabolic And quickly open 4 kinds. The only commonly used ideal flow characteristics, such as straight line, such as the percentage (logarithm), quickly open three. Parabolic flow characteristics between the straight line and equal percentage, the general percentage of the characteristics can be used instead of the other, while the fast opening characteristics are mainly used for two-bit adjustment and program control, so the selection of diaphragm pump is actually a straight line and equal percentage flow characteristics s Choice. The choice of diaphragm pump flow characteristics can be calculated theoretically, but the methods and equations used are complicated. At present, the use of more empirical criteria, specifically from the following aspects: (1) regulation of the quality of regulation from the system analysis and selection; (2) from the process of piping considerations; (3) from the load changes. Select the flow characteristics of the diaphragm pump, you can determine the valve spool according to its flow characteristics of the shape and structure, but for such as diaphragm valves, butterfly valves, because of their structural characteristics, it is impossible to change the shape of the valve spool to achieve The required flow characteristics can be achieved by changing the feedback cam profile of the valve positioner fitted. 3, the choice of diaphragm pump diaphragm Diaphragm selection and determination of the main basis for the flow of the valve that cv. In a variety of engineering instrument design and selection, should be calculated on the diaphragm cv, and provide diaphragm design instructions. Calculated from the diaphragm pump cv to determine the diameter of the valve, generally required by the following steps: (1) to determine the flow rate. The existing production capacity, equipment load and the condition of the medium determine the qmax and qmin of the flow rate. (2) Determination of the pressure difference before and after the valve. According to the selected valve flow characteristics and system characteristics selected s (resistance coefficient), and then determine the calculation of pressure. (3) Calculate cv. According to the adjusted medium to choose the appropriate formula and chart, find cmax and cmin. (4) Selection of cv. According to cmax, in the selected product standard series> cmax and the closest level c. (5) diaphragm pump opening checking. The general requirements of the maximum flow when the calculation of the opening ≯ 90%, the minimum calculation of flow when the opening ≮ 10%. (6) Diaphragm pump actual adjustable ratio checking. Generally require the actual adjustable ratio ≮10. (7) Determination of seat diameter and nominal diameter. After verification is appropriate, according to c to determine. 4, the choice of diaphragm pump type (1) diaphragm pump valve body type selection The choice of diaphragm is the most important part of the diaphragm pump. Diaphragm valve body types, commonly used through a single seat, through two-seater, angular, diaphragm, small flow, tee, eccentric rotation, butterfly, sleeve, spherical and other 10 species. Before choosing a valve, carefully analyze the medium, process conditions, and parameters of the control process, gather enough data to understand the system requirements for the diaphragm pump, and determine the type of valve to be used based on the data collected. In the specific choice, the following aspects can be considered: A, \ The shape of the valve spool is mainly based on the selected flow characteristics and unbalanced forces and other factors to consider. B, wear resistance When the fluid medium is a suspension containing high concentration of abrasive particles, the valve core, the seat surface each time the closure will be severely rubbed. Therefore, the flow of the valve should be smooth, the valve's internal material to be hard. C, corrosion-resistant As the media is corrosive, to meet the regulatory function of the situation, try to choose a simple structure of the valve. D, medium temperature, pressure When the media temperature, pressure and high changes, the valve core and valve seat material should be selected by the temperature, pressure changes in small valves. E, to prevent flash and cavitation Flash and cavitation only produce in the liquid medium. In the actual production process, flash and cavitation not only affect the calculation of flow coefficient, but also the formation of vibration and noise, so that the valve life is shorter, so the valve should be selected to prevent flash and cavitation. (2) the choice of diaphragm pump actuator A, the output power considerations Actuator no matter what type of output force is used to overcome the effective load (mainly refers to unbalanced and unbalanced torque plus friction , Sealing force, gravity and other related forces). Therefore, in order for the diaphragm pump to work properly, the associated actuator must be capable of producing enough output force to overcome various resistances and ensure a high degree of sealing and valve opening. For double-acting pneumatic, hydraulic, electric actuator, there is usually no return spring. The size of the force has nothing to do with its direction of operation, so the key to choosing an actuator lies in knowing the maximum output force and the torque of the motor. For single-acting pneumatic actuators, the output force is related to the opening of the valve. The force appearing on the diaphragm pump will also affect the kinematics and therefore a force balance across the opening of the diaphragm pump is required. B, the type of implementing agencies to determine the output of the implementing agencies to determine, according to process requirements of the use of the environment, select the appropriate implementing agencies. For on-site explosion-proof requirements, pneumatic actuators should be used, and the junction box for the explosion-proof, you can not choose the electric actuator. If there is no explosion-proof requirements, the pneumatic and electric actuators can be used, but from the energy-saving aspects, should try to use electric actuators. For the hydraulic actuator, its use is not as good as the pneumatic, electric actuators a wide range, but with high precision, fast speed and smooth characteristics, therefore, in some cases, in order to achieve better regulation effect, you must use hydraulic actuator Institutions, such as power plant transparent speed control, refinery catalytic reactor temperature control and so on. 5, diaphragm pump operation considerations (1) diaphragm pump open parking load operation diaphragm pump is driven by the variable frequency motor, if the parking load is too large or too small, easy to damage the motor. In order to avoid the emergence of the above situation, the rigid regulation of parking load is controlled at about 30%, and set in the instrument to increase or decrease the load must be completed within a period of time, effectively from the craft to do the maintenance of the inverter . (2) Diaphragm pump instrument air and lubricating oil pressure system operation Diaphragm pump instrument air and oil pressure are interlocked with the main motor, pushing the liquid oil, oil drain valve for the gas valve, to always maintain a certain air Pressure, the minimum operating pressure of the two valves is not less than 0.4mpa, so the meter air pressure is generally maintained at above 015mpa, even stop the pump after the instrument air also stop, so as not to promote the liquid in the liquid chamber is not enough or excessive air supply valve is After filtration, the oil atomized. Diaphragm pump in operation, the lubricating oil pressure should not be less than the pressure interlock value (0115mpa), and the oil outlet filter pressure can not be too large, lubricating oil flow within the scope of the ball should be in the upper limit position, adjust the flow When the adjustment range can not be too large, so as to avoid the transient flow Ambassador too much pressure drop caused by interlocking jump. Through the above process improvement and mastering the operation essentials, the diaphragm pump always has a stable process environment. After more than a year of operation, it can run in a long cycle and run safely and efficiently only once due to electrical reasons. Third, the selection of diaphragm pump In the specific selection, from the following aspects: (1) the shape of the valve core structure based on the selected flow characteristics and unbalanced forces and other factors to consider. (2) Wear resistance When the fluid medium is a suspension containing high concentration of abrasive particles, the valve core, the valve seat joint surface will be severely rubbed each time it is closed. Therefore, the flow of the valve should be smooth, the valve's internal material to be hard. (3) Corrosion resistance Due to the corrosive medium, try to choose a simple structure of the valve in the case of regulatory function. (4) Medium temperature, pressure When the medium temperature, high pressure and changes, should use the valve core and valve seat material by temperature, pressure changes in small valves. (5) to prevent flash and cavitation flash and cavitation only produce liquid medium. In the actual production process, flash and cavitation not only affect the calculation of flow coefficient, but also the formation of vibration and noise, so that the valve life is shorter, so the valve should be selected to prevent flash and cavitation.
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