Selection and application of pneumatic diaphragm control valve
September 22, 2021
As the degree of industrial automation continues to improve, as the final actuator of automatic control system, control valve gets more and more widely used. The application of control valve is directly related to the quality and safety of production. Pneumatic membrane valve selection: (1), according to the requirements of the selection Pneumatic valve diaphragm and valve body (including valve seat) composed of two parts, according to the different requirements of the use of different structures. There are: direct single-seat control valve, two-seat control valve and high-pressure angle control valve ....... Throttle through the single-seat control valve leakage is small, the thrust of the fluid on the single-seat spool unbalanced force formed by a large, so through the single-seat control valve for small leaks, small diameter and low differential pressure before and after the valve occasion. Direct through two-seater regulating valve body has two upper and lower valve spool, due to the fluid acting on the spool up and down the opposite direction and generally offset; so the two-seat valve unbalance force is small, allowing the valve before and after a larger pressure difference . However, due to the complexity of the flow path in the valve body, the erosion damage to the valve body when used for high pressure differential is more serious and should not be used for medium with high viscosity, suspended particles or fibers. In addition, due to the processing conditions, two-seat control valve up and down the two spools are not closed at the same time, so the closure of the large amount of leakage, especially in the case of high temperature or low temperature, due to different thermal expansion coefficient of the material more likely to cause Serious leaks. High-pressure angle control valve body is rectangular, simple flow path, small resistance, high-speed fluid erosion is also small, especially for high pressure, high viscosity and suspended solids particles containing fluid can also be used to handle steam Liquid mixed phase, easy flash vapor cavitation occasions. This body prevents coking, sticking and clogging for easy cleaning and self-cleaning. (2), according to the safety selection of pneumatic diaphragm valve with air valve and air valve closed in two forms. Depending on the safety of the production process and the use of requirements, when the signal pressure is interrupted when the control valve is open or closed position, the size of the hazardous process technology may be. If the valve is in the closed position harm is small, the choice of gas valve, the signal pressure is interrupted, so that the control valve is in the closed position, on the contrary, the choice of gas valve. (3), flow characteristics In the design of automatic control system, the choice of pneumatic diaphragm valve should focus on flow characteristics. Typical ideal features are linear flow characteristics, equal percentage flow characteristics (logarithmic flow characteristics), fast open flow characteristics and parabolic flow characteristics of four. Linear flow characteristics in the relative changes in the opening of the same circumstances, when the flow rate is relatively small changes in the value of flow; flow is large, the relative change in the value of small flow. Therefore, the linear flow control valve in the small opening (small load) the case of poor regulation performance is not easy to control, often produce oscillation, so the linear flow characteristics of the valve should not be used for small openings, it is not suitable for load changes Larger regulating system, but suitable for the load is relatively stable, little change regulation system. The regulating valve with percentage flow characteristics is weak in regulating action under small load and strong in regulating load. It is weak in regulating function close to closing and stable in work, while it has strong regulating function close to full opening and is sensitive and effective in work. To a certain extent, , Can improve the quality of regulation, so it is suitable for load changes in the larger occasions, both in full load and half load production are better play a regulatory role.
