One, consider from the aspect of output force
In order to make the regulating valve work normally, the equipped actuator should be able to produce enough output force to overcome all kinds of resistance, to ensure the high sealing and valve opening. For double acting pneumatic, hydraulic, electric actuators, there is generally no reset spring. The magnitude of the acting force is independent of its running direction. Therefore, the key to select the actuator is to find out the maximum output force and the rotation torque of the motor. For single-acting pneumatic actuator, the output force is related to the valve opening, the force on the control valve will also affect the movement characteristics, so it is required to establish a force balance in the whole control valve opening range.
Second, from the regulating valve action mode
The action mode of regulating valve is only in the selection of pneumatic actuator, its action mode through the positive and negative action of the actuator and the combination of positive and negative action of the valve. There are four types of combination: positive and negative (gas-off type), positive and negative (gas-open type), positive and negative (gas-open type), positive and negative (gas-open type), positive and negative (gas-open type), negative and positive (gas-open type), and negative (gas-closed type). Through these four types of combination, the regulating valve can act in two ways: gas-open and gas-close. For the selection of regulating valve action mode, the main consideration is from three aspects: a) process production safety; B) characteristics of the medium; C) ensure product quality and minimize economic losses.
Three, from the characteristics of the control valve
Regulating valve flow characteristics refers to the relative flow of the medium flow through the valve and displacement (relative opening of the valve) relationship, ideal flow characteristics mainly have straight line, equal percentage (logarithm), parabola and fast open 4, commonly used ideal flow characteristics only straight line, equal percentage (logarithm), fast open three. Parabolic flow characteristics between straight line and equal percentage, generally can be replaced by equal percentage characteristics, and fast opening characteristics are mainly used for two-position regulation and program control, so the selection of regulating valve characteristics is actually the choice of straight line and equal percentage flow characteristics.