The diaphragm pump, also known as the control pump, is the main type of actuator that uses a power operation to change fluid flow by accepting the control signal from the modulating 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. Diaphragm Pump Overview There are four pneumatic diaphragm pump material: plastic, aluminum, cast iron, stainless steel. Electric diaphragm pump which has four kinds of material: plastic, aluminum, cast iron, stainless steel. Membrane diaphragm diaphragm according to different liquids were nitrile rubber, neoprene rubber, fluorine rubber, PTFE, polytetrahexaethylene, to meet the needs. Placed in a variety of special occasions, used to pump a variety of media. Diaphragm pump type diaphragm pump according to its executive agency using the power, can be divided into pneumatic, electric, hydraulic three, namely compressed air as the power source pneumatic diaphragm pump to electric power source electric diaphragm pump, In the liquid medium (such as oil) pressure-driven electro-hydraulic diaphragm pumps, 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. Diaphragm pump body type 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 circumstances to meet regulatory functions. (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. Diaphragm pump actuator choice (1) output force 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, seal 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 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. The mode of action The function of the diaphragm pump is selected only when the pneumatic actuator, 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. The selection of flow characteristics The flow characteristics of the diaphragm pump refer to the relationship between the relative flow of the medium flowing through the valve and the displacement (the relative opening of the valve). The ideal flow characteristics are mainly straight line, equal percentage (logarithm), parabola and quick opening 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.
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