Pneumatic diaphragm control valve selection
- - - - - - - - - - - - : . Selection according to the requirement of pneumatic membrane control 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. 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. 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. 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, facilitate cleaning and self-purification. 。 According to the security type 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. 。 Flow characteristic in the design of the automatic control system in the process of choosing pneumatic diaphragm regulating valves flow characteristic 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, flow hour flow 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 the weak regulation, work smooth gentle, fully open and close to adjust action is strong, a sensitive and effective work in extent, can adjust the quality, so it is suitable for the load change is bigger, both in full load production and half load production better regulating role. 。 The regulating valve diameter should be selected according to the known fluid required to calculate the flow coefficient CV, then according to the product technical parameter table to select suitable regulator caliber. When calculating the CV to the attention of the liquid, gas, water vapor and other difference of steam. The installation of the pneumatic diaphragm valve regulating valve installation is reasonable, not only relates to the regulator of the installation, disassembly and convenient maintenance or not, also determines the regulator in the automatic control system can play a good role in regulating, the following points should be paid attention to when install regulator (1) the regulator shall be installed in horizontal pipe runs vertically, if under special circumstances need level and tilt when installation, general to add support. (2) in order to prevent the regulator diaphragm aging, prolong service life, when installation should as far as possible away from high temperature, vibration and severely corrosive environment. (3) in order to facilitate maintenance, regulating valve should be installed near the ground or floor, in order to maintenance convenient disassembly, attention should be paid to the regulator (off the ground Or the floor) With adequate height, for the gas open control valve, due to remove the need to take out from beneath the body when the valve core, regulator valve (from ground Or the floor) More should have enough distance. (4) in order to control valve and control system failure does not affect the production and safety accidents occur, are generally need to install the bypass and the bypass valve. But the bypass valve cannot be installed in the valve, in order to avoid the bypass valve leakage of corrosive medium to the regulator. Globe valve regulating valve before and after installation, for high temperature and high pressure, high pressure, easy to cold, easy to viscous medium, and the installation of a drain valve.