From the overall point of view of the control system, whether a control system is well controlled or not is realized by adjusting the valve. Regulating valves become very important for the following reasons.
(1) Regulating valve is a throttling device, which belongs to moving parts. Compared with detection elements, transmitters and controllers, in the process of control, regulating valve needs to constantly change the flow area of throttling parts, so as to change the operating variables to adapt to the changes of load or operating conditions. Therefore, higher requirements are put forward for the sealing, pressure resistance and corrosion of the control valve assembly. For example, the seal will increase the friction of the control valve, increase the dead zone of the control valve, and cause the control quality of the control system to deteriorate.
(2) The movable parts of the control valve are the main causes of "running", "running", "dropping" and "leaking". It not only wastes resources or materials, but also pollutes the environment and causes accidents.
(3) The direct contact between the valve internals and the process medium of the control valve, and the difference between the contact between the detection element and the process medium are as follows.
A. The contact medium of the valve assembly may be different from the contact medium of the testing element, which has higher requirements for the corrosion resistance, strength, stiffness and material of the valve.
B. Inspection elements can be separated from process medium by means of isolation fluid, but the control valve usually contacts process medium directly, so it is difficult to adopt isolation method and process.
Medium isolation.
(4) The throttling of the control valve makes the energy consumed in the inner parts of the valve. Therefore, reasonable selection and consideration should be taken between reducing energy consumption, reducing pressure loss of the control valve and ensuring better control quality.
_Regulating valves throttle the fluid and cause noise at the same time. For example, flash occurs when the outlet pressure of the valve is lower than the vapor pressure of the liquid, and cavitation occurs when the downstream pressure of the valve is higher than the vapor pressure of the liquid. The noise caused by the control valve is related to the design of the flow path, the operating pressure and the characteristics of the controlled medium. Therefore, reducing the noise and pressure loss put forward higher requirements for the control valve.
The adaptability of the control valve is strong. It is installed in various production processes. The operating conditions of low temperature, high temperature, high pressure, large flow and small flow in the production process require that the control valve has various functions. The control valve should be able to meet the requirements of different applications.
_Detection components and transmitters, controllers and other rapid development, investment in human and material resources. Relatively speaking, it is generally believed that the structure of the control valve is simple, so the manpower and material resources invested in the research and development of the control valve are relatively insufficient.
