2.2 Control Valve Selection of implementing agencies
2.2.1 consider the output power
No matter what kind of executive body type, the output power are used to overcome the effective load (mainly refers to the imbalance and the imbalance torque plus friction, sealing force, gravity force and so on). Therefore, in order to enable the valve to work with the implementing agencies to use to be able to generate sufficient output power to overcome all kinds of resistance, to ensure a high degree of sealing and the valve open.
Dual role for pneumatic, hydraulic, electric actuator, generally did not reset the spring. The size of force and its direction has nothing to do, therefore, to choose the key implementing agencies to ascertain the maximum output force and torque motor rotation. The role of the single executive body of the pneumatic, the output force and the opening of the valve, regulating valve on the emergence of the power will also affect the motion characteristics, it requires the opening of the regulating valve to establish equilibrium range.
2.2.2 Determination of the type of executing agency
Output force of the implementing agencies are identified, the use of environmental requirements according to process, select the appropriate enforcement agency. For the scene, where explosion-proof requirements, implementing agencies should use pneumatic and explosion-proof junction box for the type, can not choose the electric actuator. If there is no explosion-proof requirements, pneumatic, electric actuator can be selected, but to consider energy conservation should be the executing agency for electric choice. Executing agency for the liquid, its use as pneumatic and electric actuator extensive regulation accuracy but with high speed and smooth movement characteristics, therefore, in some cases, in order to achieve better regulation of the effect of liquid must be selected implementing agencies, such as power plants transparent machine speed regulation, the refinery's catalytic cracking unit reactor control temperature regulation.
3 The role of valve options
The role of regulating valve means only when the optional pneumatic before executing agency, and its executive body adopted the role of positive and negative role and valve combination of positive and negative role in the formation. There are four kinds of combinations that are (gas-off), both positive and negative (open air-type), in any case (open air-type), counter (air-off), formed through the combination of these four modes of control valve gas two open gas clearance. Regulating valve for the choice of the mode of action, mainly in three aspects to consider: a) Process of production safety; b) the characteristics of media; c) to ensure product quality, minimize economic losses.
Flow regulating valve 4, the choice of characteristics
Control valve flow characteristics of the media refers to the relative flow through the valve flow and the displacement (relative valve opening) the relationship between the ideal flow characteristics of the main straight, and the percentage (logarithmic), and soon to open, such as parabolic four kinds of , the ideal flow characteristics of commonly used only a straight line, such as the percentage (logarithmic), quickly open the three. Parabola and a straight line between the flow characteristics, such as the percentage between the percentage of the general characteristics can be used to replace and so on, and soon to open for the two main characteristics of regulation and control, and therefore the choice of control valve characteristics and is actually a straight line features, such as the percentage of flow choice.
Control valve flow characteristics through the choice of theoretical calculations, but the methods and equations is complex. At present, guidelines for the use of the experience of specific aspects from consideration: ① conditioning systems from the analysis of the regulation of quality and choice; ② piping from the process considered; ③ from the analysis of changes in load.
The choice of a good control valve flow characteristics can be determined in accordance with its flow characteristics of the valve spool of the shape and structure, but like valve, butterfly valve and so on, because of their structural characteristics, it is not possible to change the valve core with the surface shape to achieve flow characteristics needed, then, can be allocated by changing the valve positioner feedback form to achieve the cam. ball valve Trunnion Mounted Ball Valve Floating Ball Valve Top Entry Ball Valve Three way ball valve V Type Ball Valve
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