Pneumatic diaphragm valve structure and the selection requirements

A kind of pneumatic diaphragm valve is a valve type, the user choose, which need to pay attention to when pneumatic diaphragm regulating valves, what are the requirements, first of all know what is of the structure and principle of the valve? A, the working principle of pneumatic diaphragm regulating valves, pneumatic diaphragm regulating valve is pressure regulator to signal, the input air chamber of pneumatic actuators, generate thrust, by connecting rod drive valve core, a corresponding displacement & ndash; Namely, as a result of the change of valve core position of valve flow area change, so as to achieve the purpose of regulating medium flow. Second, pneumatic diaphragm regulating valves, pneumatic membrane structure regulating valve by pneumatic diaphragm actuator and control valve of two parts. Pneumatic diaphragm control valve is mainly composed of air chamber, thin films, thrust plate, springs, push rod, adjusting nut, valve rod, valve stem, valve core and valve body, valve seat, packing box, cover and bracket, etc. Third, pneumatic diaphragm regulating valves 1, according to the requirement of type selection of type pneumatic diaphragm regulating valve by valve core and valve body ( Including the seat) Two parts, according to the requirements of the use of different have different structure forms, pneumatic diaphragm regulating valves are mainly through single-seat valve, two-seat regulator and pressure Angle regulator. 一个。 Through small single-seat valve leakage, fluid of single seat valve core is formed by the thrust of unbalanced force is very big, so direct single seat valve is suitable for the requirements of small, small diameter and valve leakage at a lower pressure difference before and after. b。 Direct two-seater valve body with two valve core, because the fluid ACTS on the direction of thrust fluctuation valve core to roughly offset; So the two-seater valve unbalanced force is small, allows for a larger pressure difference before and after the valve. Due to the complex body flow, bad to the body when applied to high erosion damage is serious, should not be used in high viscosity, medium containing suspended particles or fiber. In addition, due to the limitation of processing conditions, two-seat valves up and down two valve core is not easy to locked, at the same time so close leakage, particularly in situations of high and low temperatures, due to the thermal expansion coefficient of material is different, are more likely to lead to serious leakage. c。 Angle type high pressure relief valve is right Angle type, flow is simple, small resistance, erosion by high velocity is small, especially suitable for high pressure, high viscosity and poor quality fluid containing suspended particle synthesis, can also be used to deal with vapor liquid miscible, easy to flash steam corrosion occasion. The body can avoid coking, bonding and congestion. 2, according to the flow characteristic selection in control system design in the process of selection of flow characteristics of pneumatic diaphragm regulating valves should be considered. The properties of the ideal typical linear flow characteristics, such as percentage flow characteristics ( Logarithmic flow characteristic) , quick opening four flow characteristic and parabolic flow characteristics. Linear flow characteristic in the same relative opening degree change, traffic hours, traffic relative value changed; Large flow, the flow relative change value is small. Therefore, linear flow regulator in a small open degree ( Small load) Cases regulation performance is bad, not easy to control, tend to produce oscillation, so the linear flow characteristic of regulator should not be used for small open degree, also should not be used for load change larger regulating system, and is suitable for the load is more stable, little change of regulation system. Percentage flow characteristic of regulating valve in a small load regulation is weak, big load regulation is strong, it is close to closing weak regulation, work smooth gentle, fully open and close to adjust action is strong, sensitive and effective work, to a certain extent, can improve the regulating quality, so it is suitable for the occasions with higher load, whether in the full load production and half load production can have better adjustment. 3, the regulating valve diameter should be selected according to the known fluid required to calculate the flow coefficient CV value, then according to the product technical parameter table to select suitable valve diameter. When calculating the CV value must pay attention to the liquid, gas, water vapor and other difference of steam. Flow coefficient of the CV value is valve, regulating valve and other industrial important process parameters and technical indicators of the valve. Correct calculation and selection of CV value is the important step in the protection of the normal work of pipeline flow control system. The flow coefficient ( CV value) Definition: refers to the unit time, maintaining pressure pipe in the test conditions, pipeline medium volume flow through the valve, or the mass flow rate. The maximum flow capacity of the valve. CV must pass the test and calculation of the valve. 4, according to security selection pneumatic diaphragm regulating valves have spirit opening valve and closing valve two forms. According to different considering the safety and use requirements of production technology, to be interrupted when the signal pressure regulating valve is in open or closed position, to process the harmfulness caused by size. If the valve is in closed position when the damage is small, choose open air valve, pressure signal is interrupted, the regulating valve in the closed position, on the other hand, the selection of gas valve closed.