Diaphragm pump, also known as the control pump, is the main type of actuator. It uses a power operation to change fluid flow by accepting the control signal from the control unit. Diaphragm pump generally 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. Pneumatic diaphragm pumps have four materials: aluminum, cast iron, plastic, stainless steel. Membrane electric pump diaphragm there are four materials: aluminum, cast iron, plastic, stainless steel. Diaphragm pumps are based on different liquid media were nitrile rubber, neoprene, Viton, polyvinylidene fluoride, polyhexamethylene. To meet the needs. Placed in a variety of special occasions, used to pump the kind of conventional pump can not suction medium. A diaphragm pump type diaphragm pump according to its allocation of the implementing agencies using the power can be divided into pneumatic, electric, hydraulic three, namely the compressed air as the power source of the pneumatic diaphragm pump to electric power source of the electric diaphragm Pump, liquid medium (such as oil, etc.) pressure-powered electro-hydraulic diaphragm pump, in addition, according to their functions and characteristics of points, as well as solenoid valve, electronic, intelligent, field bus diaphragm pump. 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. Second, the choice of diaphragm pump diaphragm valve 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, 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: (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 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. 2. Diaphragm pump mode of action Diaphragm pump action is only used in the selection of pneumatic actuators 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 minimum. 3. Diaphragm pump flow characteristics of the selection Diaphragm pump flow characteristics refers to the medium flow through the valve relative displacement and displacement (the valve relative 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 experience guidelines, specifically from the following aspects: â‘ from the regulatory system to adjust the quality of analysis and selection; â‘¡ from process piping considerations; â‘¢ 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. The choice of diaphragm pump actuator (1) 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. (2) Determination of the type of implementing agency After determining the output of implementing agencies, select the appropriate implementing agencies according to the requirements of the environment for process use. 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 pneumatic, electric actuator widely, but with high precision, fast and smooth movement characteristics, therefore, in order to achieve better regulation effect, you must choose the implementation of hydraulic Institutions, such as power plant transparent speed control, refinery catalytic reactor temperature control and so on. 5. Diaphragm Pump Diaphragm Diaphragm Selection and Determination of Mainly based on the valve flow 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. The existing production capacity, equipment load and the condition of the medium determine the Qmax and Qmin of the flow rate. (2) before and after the valve to determine the pressure difference. 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 Cmax and Cmin. (4) choose Cv. According to Cmax, choose Cmax and the closest level C in the selected product standard series. (5) diaphragm pump checking. The general requirements of the maximum flow when the calculation of 90% of the opening, the minimum calculation of flow when the opening of 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. Three diaphragm pump operation Notes: 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, short run Juan brake? In order to avoid the above situation, rigidly stipulate the parking load should be controlled at about 30%, and set in the instrument so that the increase or decrease of load must be completed within a certain period of time , Effective from the craft done on the inverter maintenance. 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 air valve, to always maintain a certain air pressure , The minimum operating pressure of the two valves is not less than 0.4MPa, so the instrument air pressure is generally maintained at above 015MPa, stop the meter air even after stopping the pump, so as not to promote the liquid in the liquid chamber is not enough or excessive, the air supply valve is through Filtration, oil atomized. Diaphragm pump in operation, the lubricating oil pressure should not be less than the pressure interlock value (0115MPa), and the lubricating oil outlet
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