Overview of Control Valve Standards

Overview of Control Valve Standards:



At present, in the field of automatic control, whether a process can meet various process control indicators, whether the control process is stable, whether overshoot, attenuation ratio, and interference are within the specified range, whether it is stable, fast, and accurate, in addition to reasonable process design, whether the regulating valve can act correctly according to the consciousness of the subject, and the control consciousness of the process subject is the correct change of material energy and flow rate



In automatic control, due to poor quality of regulating valves, poor flow characteristics, large leakage, and unreliable operation, automatic control loses high-quality regulation, causing huge economic losses to production and increasing labor intensity.



Due to the installation of the regulating valve on the process pipeline, it is in direct contact with the operating medium and has been subjected to harsh working conditions such as high temperature, high pressure, corrosion, and friction for a long time. Therefore, the selection of regulating valves is closely related to system control. Therefore, it is particularly important to choose and install regulating valves correctly and reasonably.



Selection of regulating valve products:



△ Direct single seat regulating valve: simple structure, easy assembly, small leakage, but unbalanced by fluid impact, suitable for small diameter applications.



△ Direct dual seat regulating valve: less affected by fluid impact imbalance, but not tightly closed, with large leakage, suitable for large diameter pipelines.



Angle regulating valve: The valve body of the angle regulating valve is less affected by fluid impact and less prone to fouling, making it particularly suitable for fluids with high viscosity and floating materials.



Butterfly valve: With low flow resistance, it is suitable for gases with low pressure differentials and media containing suspended solids. Its flow characteristics are usually similar to those of an equal percentage.



Diaphragm control valve: used for media with strong corrosiveness, high viscosity, and high fiber content, but not resistant to high temperature and high pressure.



△ Three way regulating valve: suitable for three-way flow, divided into three-way valve and three-way valve, it is very effective in controlling the flow of the three systems.



△ Wheel flex valve: It belongs to a new structure valve, with a DC valve body, low resistance, good sealing performance, adjustable, strong universality, and very effective in regulating media with high viscosity.



△ Sleeve regulating valve: A new type of structural valve is widely used in production due to its low unbalanced force, good adjustability, strong universality, and easy maintenance, especially for media with high temperature, high viscosity, and particle structure.



Application principle of regulating valve:



The regulating valve consists of an actuator and a valve body. Including feeding function, receiving unified 4-20mA or 1-5V DC standard signal converts the current signal into corresponding linear displacement, automatically controls the opening of the regulating valve, and continuously adjusts the process parameters such as pressure, flow rate, temperature, and liquid level of the fluid in the pipeline. Widely used in the production automation control of industrial sectors such as power, metallurgy, chemical, petroleum, textile, pharmaceutical, and papermaking.



Regulating valve, also known as flow control valve. In the field of industrial automation process control, by receiving control signals output by the regulating control unit, the regulating valve can change the final control components of process parameters such as medium flow rate, pressure, temperature, and liquid level through power operation. It is generally composed of an actuator and a valve. According to the characteristics of the stroke, regulating valves can be divided into straight stroke and angular stroke; According to the power used by the actuator, it can be divided into linear characteristics, proportional characteristics, and parabolic characteristics based on its function and characteristics. Suitable for air, water, steam, various corrosive media, mud, oil and other media.



Selection of regulating valve diameter:



When transforming automatic technology, the diameter of the regulating valve can be considered based on the principle of equal cross-sectional area. The opening area can be estimated based on the diameter of the valve and the number of opening rings during manual operation, and then the regulating valve with the same opening area under normal working conditions can be selected. When designing new equipment, the valve diameter is usually determined based on the flow capacity C value.



There are two commonly used methods.



(1) Calculate the corresponding flow capacity Cmax based on the actual high flow rate Qmax, and then select a C value slightly larger than Cmax and the corresponding regulating valve diameter from the product series, leaving necessary space when selecting. Then calculate the valve opening at the actual high flow rate Qmax: the opening at Qmax should not exceed 90%.



② A more practical method is to calculate the corresponding circulation capacity Cvc based on commonly used traffic. The C value for selecting a regulating valve should be between 0.25 and 0.8, which is calculated by multiplying the commonly used flow rate Cvc value by (4~1.25). Generally, Cvc/C=0.5 is appropriate. When the working characteristic is logarithmic, it can be smaller.



Precautions for installation of regulating valve:



(1) Valves should be installed vertically on horizontal pipelines, known as regulating valves with DN ≥ 50, and there should be permanent supports in the front and rear pipelines of the valve.



(2) The installation location should be convenient for operation and maintenance, so that personnel can carry out maintenance and operation. If necessary, a platform should be set up.



(3) There should be sufficient space in the upper and lower parts to allow for the removal of the actuator, valve components, and the lower flange and plug of the valve during maintenance.



(4) When installing regulating valves during vibration, anti vibration measures should be considered.



(5) Install a small pressure gauge on the diaphragm head to indicate control signals for regulating valves without valve positioners installed.



(6) The regulating valve should be inspected, checked, and installed after pipeline cleaning.