What Are Control Valves?

Control valve (Control valve) is composed of two main assemblies: valve body assembly and actuator assembly (or actuator system), divided into four series: single seat series control valve, double seat series control valve, sleeve Cylinder series control valve and self-operated series control valve. Variations of the four types of valves can lead to many different applicable structures, each of which has its particular application, features, advantages and disadvantages. Although some control valves have a wider range of application conditions than others, control valves are not suitable for all conditions in order to jointly build the best solution to enhance performance and reduce costs.

1. There are various types of control valves, and their applicable occasions are different. Therefore, the type of control valve should be reasonably selected according to the requirements of the process of production.

2. Pneumatic control valve is divided into two types: air on and air off. The air-open control valve is closed in the fault state, and the air-open control valve is opened in the fault state. Some auxiliary equipment can be used to form the retention valve or make the control valve self-locking, that is, the control valve maintains the valve opening degree before the fault when the fault occurs.

Gas open and

From the perspective of control valve applications, the development direction is as follows:

1. Small executive agencies: can reduce costs and improve circulation capacity;

2. Sleeve guidance: The use of sleeve guidance facilitates centering, reduces friction, reduces noise, and facilitates interchange of flow characteristics;

3. Balanced spool: In order to reduce the thrust or thrust of the actuator, it is important to use a balanced spool, which also improves the dynamic performance of the system;

4. Integrated valve core and valve seat: To overcome the shortcomings of the poor sealing performance of the double seat valve, the integrated valve core and valve seat of the same material are used to form the valve trim to minimize leakage and unbalanced force at the same time;

5. Simple flow path: The flow path is simple and the flow resistance is reduced, which can not only reduce the pressure loss at both ends of the valve, but also reduce the cost;

6. Sealing and friction: Sealing performance and friction performance are two contradictory aspects. Not only the sealing problem must be solved in the design of the control valve, but also performance indicators such as friction and life must be paid attention to. Therefore, research on stuffing box and packing structure has been paid attention to, and rotary control Valves are widely used;

7. Noise reduction: reduce the noise of control valves in various ways, for example, using noise reduction sleeves and spools, multi-stage spools, noise reduction restrictors, expanders, etc .;

8. Control valve with the same diameter as the pipeline and valve trims that limit the flow capacity: It is beneficial to reduce the inlet pressure and outlet fluid flow rate of the valve, and it is not necessary to install additional fittings such as reducers, which is beneficial to reducing costs. By replacing the valve with large flow capacity, It can expand the flow capacity, and the error of over-calculation caliber can be corrected by selecting the valve flow limiting internal parts;

9. In the digital information age, it will be more adopted

   The hydraulic water level control valve has the function of automatically opening and closing the valve pipeline to control the water level. It is suitable for the automatic water supply system of various water towers (pools) in industrial and mining enterprises and civil buildings. It can also be used as a circulating water supply control valve for atmospheric boilers. Easy installation, high activation sensitivity, small head loss and no water hammer. Controlled by a small floating ball can greatly increase the utilization rate of the water tower. For newly built water towers, the upper part of the water tower is left to the height required for the floating ball to float freely due to the reduced volume of the floating ball. It can reduce the production of water tower, overcome the disadvantages of the old-fashioned floating ball valve, which is bulky, easy to damage, low working pressure, and large amount of overflow. ^[2]

   The control valve has the characteristics of simple structure and reliable operation, but because it directly contacts the process medium, its performance directly affects the system quality and environmental pollution. Therefore, the control valve must be regularly maintained and regularly overhauled, especially for the harsh and important operating conditions. Occasions, more attention should be paid to maintenance work. Key inspection sites:

   1.The inner wall of the valve

   For control valves used in high-pressure differential and corrosive media, the inner wall of the valve and the diaphragm of the diaphragm valve are often subject to the impact and corrosion of the medium. The pressure and corrosion resistance must be checked.

   2.Valve seat

   When the control valve is working, due to the infiltration of the medium, the threaded inner surface of the fixed valve seat is susceptible to corrosion and the valve seat becomes loose. Pay attention during inspection. For valves operating under high pressure differentials, it should also be checked whether the sealing surface of the valve seat is damaged.

   3.Spool

   Selection of regulating valve actuator

   In order to make the regulating valve work normally, the matched actuator must be able to produce sufficient output force to ensure a high degree of sealing and valve opening.

   For double-acting pneumatic, hydraulic and electric actuators, there is generally no return spring. The magnitude of the force has nothing to do with its running direction. Therefore, the key to selecting the actuator is to find out the maximum output force and the rotating torque of the motor. For a single-acting pneumatic actuator, the output force is related to the opening degree of the valve, and the force appearing on the regulating valve will also affect the motion characteristics, so it is required to establish a force balance throughout the opening range of the regulating valve.

   Determination of the type of actuator

   After determining the output force of the actuator, select the corresponding actuator according to the requirements of the process environment. For on-site explosion-proof requirements, pneumatic actuators should be selected. From the perspective of energy saving, electric actuators should be selected as far as possible. If the adjustment accuracy is high, a hydraulic actuator can be selected. Such as power plant turbine speed adjustment, refinery catalyst reactor temperature adjustment control. ^[2]