Diaphragm Pump Introduction Pump is a wide range of general-purpose machinery and equipment, it is widely used in petroleum, chemical, power metallurgy, mining, ship selection, light industry, agriculture, civil and defense departments, in the national economy is important Position. According to the statistics of 79 years, the pump output in our country reached 1,256,000 units, which has far exceeded this figure up till now. The main ones such as vacuum pump and Centrifugal Pump may all know, but there are many kinds of pumps which may be a little more popular but still use A very wide range, for example: The following introduces the diaphragm pump related knowledge 1 diaphragm pump composition and classification diaphragm pump, also known as the control pump, is the main type of actuator, by adjusting the control unit to receive the control signal output, with power to operate Change fluid flow. Diaphragm pump generally by the implementing agencies and valves. If you press the actuator used by its power, the diaphragm pump can be divided into pneumatic, electric, hydraulic three, namely compressed air as the power source of the pneumatic diaphragm pump to electric power source electric diaphragm pump to liquid medium (Such as oil, etc.) pressure-driven electro-hydraulic diaphragm pumps, in addition, according to their functions and characteristics of points, as well as solenoid valves, electronic, intelligent, field bus diaphragm pumps. Diaphragm pumps are many types of products, the structure is also diverse, but also constantly updated and changing. Generally speaking, the valve is universal, it can be matched with the pneumatic actuator, but also with the electric actuator or other actuator. 2 diaphragm pump mode of action The role of the diaphragm pump is selected only when the pneumatic actuator only, the role of the positive and negative 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 diaphragm pump mode of action, mainly from three aspects: a) process safety; b) the characteristics of the media; c) to ensure product quality, economic loss is minimal. 3 diaphragm pump flow, the choice of characteristics Flow characteristics of the diaphragm pump refers to the relative flow of the medium through the valve displacement and displacement (the relative opening of the valve) relationship between the ideal flow characteristics are straight, equal percentage (logarithm), parabolic And fast open, etc. 4, the characteristic curve and spool shape shown in Figure 1 and Figure 2. 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 experience guidelines, specifically from the following aspects: ①from the regulatory system to adjust the quality of analysis and selection; ② from process 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. 4 Diaphragm Pump Selection 4.1 Diaphragm Pump Body Type Selection The choice of diaphragm is the most important part of the diaphragm pump selection. 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 to collect enough data. The diaphragm pump understands the system's requirements for the diaphragm pump and determines the type of valve to be used based on the data collected. In the specific choice, the following aspects can be considered: (1) spool shape and 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 concentrations of abrasive particles, the diaphragm pump, valve seat joints will be severely rubbed each time they are 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 temperature of the medium, the diaphragm pump pressure is high and the change is large, the valve and valve seat material should be selected by the valve temperature and pressure changes small. (5) diaphragm pump to prevent flash and cavitation flash and cavitation only generated 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. 4.2 The choice of diaphragm pump actuator 4.2.1 Diaphragm pump output power considerations Regardless of the type of actuator, diaphragm pump output force is used to overcome the effective load (mainly refers to unbalanced force and unbalanced torque plus On the friction, sealing force, gravity and other related forces). Therefore, in order for the diaphragm pump to work properly, the diaphragm pump is equipped with an actuator that can generate 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. 4.2.2 diaphragm pump actuator to determine the type of actuator output force is determined, according to process requirements of the use of the environment, select the appropriate actuator. For on-site explosion-proof requirements, pneumatic actuators should be used, diaphragm pumps and explosion-proof junction box, 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. Diaphragm pumps for hydraulic actuator, its use is not as good as pneumatic and electric actuators, but with high precision, diaphragm pump speed and smooth movement characteristics, therefore, in some cases, in order to achieve better regulatory effect, it must Selection of hydraulic actuators, such as power plant transparent machine speed regulation, refinery catalytic reactor temperature control and so on. 5 Diaphragm Pump Diaphragm Diaphragm selection and determination of the main valve based on the flow of capacity that Cv. In a variety of engineering design and selection of instruments, should be on the diaphragm Cv calculations, diaphragm pumps and provide design specifications. 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. Existing production capacity, diaphragm pump equipment load and the condition of the medium, to determine the flow Qmax and Qmin.2) Determination of pressure 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. Diaphragm pump according to the adjusted medium to choose the appropriate formula and chart, obtained Cmax and Cmin.4) choose Cv. According to Cmax, in the selected product standard series choose> Cmax and its 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. General requirements of the actual adjustable ratio ≮ 10.7) Determination of seat diameter and nominal diameter. After verification, according to C to determine. 6 Conclusion diaphragm pump selection is a very meticulous work, not only have a solid professional theoretical knowledge, but also have rich practical experience. Good choice not only conducive to adjusting the control loop PID parameter setting, so that the parameters are to be tuned to better control effect, but also greatly increase the service life of the diaphragm pump. The choice of diaphragm pump should be adapted to local conditions and not static. To summarize and innovate constantly in the process of practice, especially with the application of mechatronics, computer and digital information technology, the structural function of diaphragm pump becomes better and more comprehensive, For the choice of diaphragm pump provides a great convenience.
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