一、An overview of regulating valves
The regulating valve is used to regulate the flow, pressure, temperature, liquid level and other parameters of the medium.
According to the signal output by the controller, automatically control the opening of the valve, change the adjustment parameters, and control the adjusted parameters within the required range, so as to achieve the process
Production automation.
• Regulating valves are divided into pneumatic, hydraulic and electric according to their energy forms.
• Pneumatic regulating valves are divided into film type, piston type and long-line program according to their actuator form.
• Electric and hydraulic regulating valves are divided into straight stroke and angular stroke according to the movement of the actuator.
At present, pneumatic regulating valves are commonly used in the petrochemical industry, electric regulating valves are rarely used, and hydraulic regulating valves are only used under special requirements.
• Circulation capacity Cw is one of the main parameters for selecting the regulating valve. The circulation capacity of the regulating valve is defined as: when the regulating valve is fully open, when the pressure difference between the two ends of the valve is 0.1MPa, and the fluid density is 1g/cm3, the flow rate flowing through the regulating valve per hour is called the circulation capacity, also known as the flow coefficient, in Cv
It means that the unit is t/h, and the Cv value of the liquid is calculated as follows.
According to the size of the Cv value of the circulation capacity, the nominal diameter DN of the regulating valve can be determined.
• The flow characteristic of the regulating valve is the relationship between the relative flow of the medium flowing through the regulating valve and its opening under the condition that the pressure difference between the two ends of the valve is constant. The flow characteristics of the regulating valve include linear characteristics, equal percentage characteristics and parabolic characteristics. Three kinds of betting special Jie Shangyi Fork League
1) The relative stroke and phase of equal percentage characteristics (logarithm) and equal percentage characteristics
/ There is no linear relationship with the flow. The change of flow caused by the change of the unit stroke at each point of the journey is directly proportional to the flow at this point, and the percentage of the flow change is equal. Therefore, its advantage is that the flow rate is small and the flow change is small. When the flow is large, the flow change is large, that is, it has the same adjustment accuracy at different openings.
(2) Linear characteristics (linear) The relative stroke and relative flow of linear characteristics are linearly related. The flow change caused by the change of the unit itinerary is unchanged.
When the flow is large, the relative value of the flow changes small, and when the flow is small, the relative value of the flow changes greatly.
3) The parabola characteristic flow varies proportionally to the two sides of the stroke, and generally has the intermediate characteristics of linear and equal percentage characteristics.
From the analysis of the three characteristics, it can be seen that in terms of its adjustment performance, the equal percentage characteristics are the best, and its adjustment is stable and the adjustment performance is good. And the parabolic characteristics have better adjustment performance than linear characteristics, and any of the flow characteristics can be selected according to the requirements of different occasions of use.
2./Regulating mechanism:
• The regulating mechanism is mainly composed of a valve core and a valve seat, which is actually a throttle element that can be changed by local resistance. The upper part of the valve stem is connected to the actuator, and the lower part
1 Connected to the valve core. Because the valve spool moves in the valve body, the circulation area between the valve core and the valve seat changes, that is, the resistance coefficient of the valve is changed, and the flow rate of the controlled medium also changes accordingly, so as to achieve the purpose of controlling the process parameters.
• The types of regulating mechanisms mainly include straight-through single-seat, direct double-seat control valves, angular control valves, three-way control valves, diaphragm control valves, butterfly valves, ball valves and cage valves.
I. Valve positioner
The valve positioner is the main accessory of the regulating valve. It is used with the pneumatic regulating valve. It receives the output signal of the regulator, and then the positioner outputs the signal to control the pneumatic regulating valve. When the regulating valve moves, the displacement of the valve stem is fed back to the valve positioner through the mechanical device, forming a closed-loop loop.
According to the types of on-site regulating valve locators, the types, installation and adjustment methods and steps of the locator are summarized. Let's briefly introduce the types of locators and the precautions for installation. The adjustment of the locator will be explained separately as a key part.
1. Types of locators
There are the following types of positioners used in the on-site regulating valve:
(1) ABB single/dual-acting locator;
(2) Fisher DVC6000 series intelligent valve
Door Positioner (3) YT-2400 Intelligent Valve Positioner; (4 Y 00 Series Outlet Valve Positioner (5) Fisher DVC2000 Intelligent Valve Positioner
• Check the installation angle of the feedback bar in the position.
Press and hold the MODE key.
At the same time, click the key or the key until the operation mode code 1.3 is displayed.
Release the MODE button.
Use the public and • keys to make the actuator run to the two terminal positions respectively and record the two terminal angles.
The two angles should conform to the following recommended angle range (the minimum angle displacement is 20 degrees, no strict symmetry is required)
The application range of straight stroke is within -28°--- +28°.
The angular stroke application range is within -570--- +57°.
The angle of the whole journey should not be less than 25°.