Electric flow characteristic of regulating valve directly affect the quality of system control and stability, so you need to choose right,
Electric control valve flow characteristic points ideal flow characteristic and working flow characteristic of flow characteristic is provided by the general factory ideal flow characteristic, and practical applications need is work flow characteristic, because of the pressure drop ratio less than 1 S, work flow characteristic on convex, therefore, when choosing regulator flow characteristic, should consider to choose work flow characteristic, and then, according to the practical application of ideal flow characteristic, the ideal flow characteristic is commonly used in the production of linear, percentage and quick opening characteristics, such as the quick opening feature is mainly used for on-off control and program control, so the regulator flow characteristic of choice is usually refers to how to choose reasonable linear and percentage ideal flow characteristic, such as
In practical use, the valve is installed in the process piping system, regulating valve and the pressure difference is with the resistance of pipeline system is changing, as a result, choosing flow characteristic of regulating valve, not only should based on features of process, also should consider piping of combination system,
(1) according to the process characteristics, select the valve working flow characteristic, conventional control law is linear controller, the controller parameter setting after hope to be able to adapt to a certain scope of work, do not need to change often, this requires a generalized object is linear, namely, in case of load before the valve pressure change or set point, the characteristics of generalized object basically remain unchanged, as a result, from the view of the automatic control system, for the selecting principle of control valve operating characteristics is to make the generalized object with linear features, namely in the generalized object, in addition to regulating valve of the rest of the features (transmitter features, process feature) is linear, work should choose the linear flow characteristic of regulating valve (Kv) with constant; If transmitter features is linear, and process characteristics of amplification coefficient w is reduced with the increase of the manipulated variables, the dampers should be chosen and percentage of work flow characteristic, in short, when the generalized object (except regulator) with nonlinear characteristics, the control valve should be able to overcome its nonlinear effect and make the generalized object close to linear features,
(2) according to the situation of piping, starting from the work flow characteristic, deduce the ideal flow characteristic, the regulator is always at the scene of the production facilities used together, so inevitably there are piping resistance, make the work flow characteristics of control valve and the ideal flow characteristic, there exist certain differences, therefore, when choosing regulator characteristic, also should consider the process piping of combination system, on the basis of process piping after case, determine the pressure drop than the S value, can from the working flow characteristic of the selected, determine the ideal flow characteristic,