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°.

Valve basic knowledge

1, the basic parameters of the valve: nominal pressure PN, nominal diameter DN

2, the basic function of the valve: cut off the medium, adjust the flow, change the direction of flow.

3, the valve connection methods are mainly flange, threaded, welded, clamps

4, the valve’s pressure-temperature level: different materials, different operating temperatures, allowing no impact on the working pressure is different.

5、Pipe flange standards are mainly two systems: the European system and the U.S. system.

Two systems of pipe flange connection size is completely different, not interchangeable.

According to the pressure level to distinguish between the more appropriate:

European system for PN0.25, 0.6, 1.0, 1.6, 2.5, 4.0, 6.3, 10.0, 16.0, 25.0, 32.0, 40.0 MPa.

American system is PN1.0 (CIass75), 2.0 (CIass150), 5.0 (CIass300), 11.0 (CIass600), 15.0 (CIass900), 26.0 (CIass1500), 42.0 (CIass2500) MPa.

The main types of pipe flanges are: Integral (IF), Plate Plain Welding (PL), Necked Plain Welding (SO), Necked Butt Welding (WN), Socket Welding (SW), Screw (Th), Butt Welding Ring Loose Sleeve (PJ/SE)/(LF/SE), Flat Welding Ring Loose Sleeve (PJ/RJ), Flange Cover (BL).

Types of flange sealing surfaces are full-flat (FF), raised face (RF), concave face (FM) convex face (M), tongue-and-groove (T) groove (G) surface, ring bonding surface (RJ) and so on.

6、Cast iron valve body is not suitable for use in the following occasions

1）Water vapor or wet gas with high water content;

2）Flammable and explosive liquids;

3) Ambient temperature below -20℃;

4) Compressed gas

Control valve
1、Control valve consists of valve body and actuator and its accessories.
2、Pneumatic thin-film actuator has two forms of positive and negative action; with the increase of signal pressure, the actuator downward for positive action, and vice versa, the actuator upward for negative action; usually accepts the standard signal pressure of 20-100KPa; with the locator when the pressure is higher than 250KPa. six basic strokes (mm): 10; 16; 25; 40; 60; 100.
3、What are the characteristics of electric actuator compared with pneumatic actuator, and what kinds of output forms are there?
The driving source is electric power, simple and convenient, large thrust and torque, high rigidity. However, the structure is complex, poor reliability. In small and medium-sized specifications, pneumatic expensive. Commonly used in applications where there is no air source or where strict explosion-proof or explosion-proof is not required.
Provide three types of output: angle stroke, straight stroke and multi-turn.
4、What are the characteristics of straight-through single-seat adjustment valve? Applicable to what occasions?
(1) As there is only one spool, the drain flow is small and easy to seal. The standard drain flow is 0.01% KV, and further design can be used as a globe valve.
(2) Due to the large unbalanced force thrust, the permissible differential pressure is small. DN100 valve △ P is only 120KPa.
(3) small flow capacity. DN100 KV is only 120. suitable for use in small leakage, differential pressure occasions.
5、What are the characteristics of straight-through double-seat adjustment valve? Applicable to what occasions?
(1) the allowable differential pressure is large, because it can offset many unbalanced forces. DN100 valve △ P is 280KPa.
(2) The flow capacity is large. DN100 is 160 KV.
(3) The two spools cannot be sealed at the same time, and the leakage is large. The standard leakage rate is 0.1% KV, which is 10 times that of single-seat valve.
Mainly used in high differential pressure, leakage requirements are not strict occasions
6、What are the main advantages of sleeve adjustment valve?
Combines the advantages of single-seated and double-seated valves. The main ones are:
(1) good stability. As the spool throttling instead of the slide valve seat throttling, and the spool is equipped with a balance hole, which can reduce the unbalanced force of the medium acting on the spool. At the same time, the guiding surface of the sleeve and the spool, coupled with small changes in the unbalance force, so it is not easy to cause spool vibration.
(2) Interchangeability, versatility. Only need to replace the sleeve to obtain different flow coefficients and different flow characteristics.
3）Large permissible differential pressure and small influence of thermal expansion. The balancing principle of sleeve valve with balancing hole is the same as that of double-seat valve, so the allowable differential pressure is larger. And because the sleeve and valve plug are made of the same material, the expansion caused by temperature change is basically the same.
(4) The sleeve provides two kinds of throttling windows: large hole and small hole (injection type). The latter has the effect of reducing noise and vibration, and is further improved to be a specialized low-noise valve.
It is suitable for occasions where the pressure difference between the front and rear of the valve is large and the noise requirement is low.
7, in addition to single and double seat valves and sleeve valves, what other valves have regulatory functions?
Diaphragm valves, butterfly valves, O-type ball valves (mainly cut-off), V-type ball valves (regulation ratio, with shear effect), eccentric rotary valves.
8, the adjustment ratio of the control valve R, the ideal adjustment ratio, the actual adjustment ratio is how much?
Control valve can control the ratio of large flow and small flow is called the adjustment ratio R.
When the pressure difference between the two ends of the valve to maintain a constant, the larger flow rate and the smaller flow rate of the ratio known as the ideal adjustment ratio.
In practice, the pressure difference between the two ends of the valve is variable, the adjustable ratio is called the actual adjustable ratio.
9, what is the flow coefficient of the control valve C, Cv, KV value?
Control valve flow capacity of the size of the flow coefficient to indicate.
(1) engineering unit system Cv definition: when the control valve is fully open, the pressure difference between the valve before and after 1kgf/cm2, the number of cubic meters of water per hour through the temperature of 5 ~ 40 ℃.
(2) British system of units C definition: when the regulator valve is fully open, the valve before and after the pressure difference of 1bf/in2 (1 degree 60.F of water per minute through the US gallons of water.
(3) International System of Units KV: when the control valve is fully open, before and after the valve pressure difference of 100kPa, the temperature is 5 ~ 40 ℃, the number of cubic meters of water through the hour.
CV = 1.17KV
Voltage = 1.01°C

The regulating valve is directly installed on the process pipeline, the use of poor conditions, such as high temperature and pressure, deep freezing, extremely toxic, flammable, explosive, easy to penetrate, easy to crystallize, strong corrosion and high viscosity, its quality directly affects the quality of the system. Thus affect the quality of the final product and the efficiency of the system operation. Problems can occur if not properly selected or maintained. For example, some regulating circuits are not stable: they oscillate all the time, and if the selection is improved, the quality of regulation is greatly improved after changing the linear characteristic spool to the logarithmic characteristic spool or changing the flow direction. For example, some continuous oscillations occur in the adjustment process, not because the proportion of the regulator is too large or too small, but because the dry friction of the valve stuffing box is too large, and the action is not flexible. For example, the leakage of the regulating valve will cause factory pollution and even cause accidents. Therefore, attention should be paid to the role of the regulating valve, and maintenance and maintenance should be strengthened. What are the problems with manual control?

Above is a schematic diagram of a manually controlled level. The liquid continuously flows through the inlet valve 2 into the storage tank 1, and continuously flows out through the outlet valve 4. We can see that the liquid level in the tank will fluctuate with the inflow or outflow. When the fluctuation is serious, the liquid in the tank may overflow or be evacuated. To solve this problem and keep the level within a certain range, the simplest way is to install a glass tube level gauge 3. With the upper and lower limits of the level gauge as the standard, when the liquid level rises to close to the upper limit scale, you can open the export valve, or close the inlet valve opening; When the liquid level drops to the lower limit scale, you can close the outlet valve or open the opening of the inlet valve, so as to avoid the tank overflow due to excessive liquid level, or because of the liquid level down and the evacuation of the accident occurred, so that the liquid level remains within a certain range. This process is directly controlled by people, so it is called manual control. It can be seen that manual control has at least the following problems and thus cannot meet the requirements of modern industry for process control. 1. Poor control accuracy. When the liquid level requirements are more accurate, that is, the upper and lower limits of the liquid level change range requirements are small, because of human reflection to manual operation there is a process, resulting in excessive liquid level control. 2. Slow response time. 3. Fatigue failure. 

The pneumatic regulating valve is to use compressed gas as the power source, the cylinder as the actuator, and drive the valve with the help of valve positioner, converter, solenoid valve, position valve, gas storage tank, gas filter and other accessories to realize the switching quantity or proportional adjustment, and receive the control signal of the industrial automation control system to complete the regulating pipeline. Medium: flow, pressure, temperature, liquid level and other process parameters. The characteristics of pneumatic regulating valves are simple control, fast response, and intrinsically safe, and there is no need to take additional explosion-proof measures.

The International Electrotechnical Commission IEC defines the control valve (known as Control Valve in foreign countries) as: "The terminal component formed by a power-operated device in the industrial process control system, which includes a valve body component. There is a component inside that changes the flow rate of the process, and the valve body component It is also connected with one or more executive agencies. The actuator is used to respond to the signals sent by the control. It can be seen that the regulating valve is composed of two parts: the actuator and the valve body parts, namely:

Regulating valve = actuator + valve body parts + accessories

Among them, the actuator is the propulsion device of the regulating valve, which generates a corresponding thrust according to the size of the signal pressure, so that the putter produces a corresponding displacement, thus driving the core action of the regulating valve; the valve body component is the regulating part of the regulating valve, which is directly in contact with the medium and changes the joints of the regulating valve through the displacement of the putter rod of the actuator. Flow area, to achieve the purpose of adjustment.