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A friend asked me to share information on the applications of control valves, so after several hours of effort, I’ve summarized some practical tips to share with everyone. Introduction to Control Valves: Let’s first get a brief understanding of control valves. They belong to the category of control valves, and their primary function is to regulate parameters such as the pressure, flow rate, and temperature of a medium; they serve as the ultimate control elements in process loops. Control valves play a very important role in the automated control of modern factories, whose production depends on the proper distribution and control of flowing liquids and gases. These controls, whether it is the exchange of energy, the reduction of pressure, or simply the feeding of materials into a container, all require final control elements to carry out. The final control element can be considered the “physical energy” of automatic control. Between the low-energy level of the regulator and the high-energy level function required to control the flowing fluid, the final control element performs the necessary power amplification. And the control valve is the most widely used type of final control element. Control valves serve to provide variable resistance in pipelines. It changes the turbulence level of the process fluid or creates a pressure drop in laminar flow, with the pressure drop being caused by a change in the valve resistance or \"friction\". This pressure reduction process is commonly referred to as “throttling”. For gases, it approaches an isentropic process at constant temperature, with the deviation depending on the degree of non-ideality of the gas (Joule-Thomson effect). In the case of a liquid, the pressure is dissipated due to turbulent flow or viscous friction; in both cases, the pressure is converted into thermal energy, resulting in a slight increase in temperature. Based on their stroke characteristics, control valves can be divided into straight-stroke and angle-stroke types. Linear stroke valves include: single-seat valves, double-seat valves, sleeve valves, angle valves, three-way valves, diaphragm valves ； Angular stroke types include: butterfly valves, ball valves, eccentric rotary valves, and all-function ultra-lightweight control valves. Control valves can be classified by drive type into pneumatic control valves, electric control valves, and hydraulic control valves ； Based on the control type, they can be classified as: control type, cut-off type, and control-cut-off type ； Based on flow characteristics, they can be classified as: linear, equal percentage, parabolic, and quick-opening. Control valves are suitable for media such as air, water, steam, various corrosive substances, sludge, and oils. A self-acting control valve, also known as a self-acting regulating valve, is a type of control valve that relies on the pressure and temperature of the medium flowing through it as an energy source to operate the valve automatically, without the need for an external power supply or auxiliary instruments. Functions of self-acting control valves: 1. Direct action. Direct-acting control valves are also known as spring-loaded control valves; they contain elastic elements such as springs, diaphragms, or diaphragm-type temperature sensors, and operate on the principle of balancing the force exerted by these elastic elements with the feedback signal. 2. Indirect action: In indirect-action control valves, an additional actuator (pilot valve) is used; this valve amplifies the feedback signal, and then through the actuating mechanism, it drives the valve disc to move in order to change the degree of valve opening. In the case of a pressure control valve, the feedback signal is the outlet pressure of the valve, which is transmitted to the actuator through a signal line. In the case of a flow control valve, there is a orifice plate (or some other flow-restricting device) at the valve’s outlet; the pressure difference across this orifice plate is used to generate a signal that is fed to the actuator. In the case of a temperature control valve, there is a temperature sensor (or thermocouple) at the valve’s outlet; the expansion and contraction of the fluid inside this sensor drive the actuator. Applications of self-acting control valves: (1) Control valves are considered to be field instruments; the operating temperature should be within the range of -25 to 60°C, with a humidity level of ≤95%. If it is installed outdoors or in a high-temperature environment, moisture-proof and temperature-reducing measures should be taken. In areas with seismic sources, it is necessary to eliminate those sources or enhance vibration isolation measures. ⑵Control valves should generally be installed vertically; in special cases, they can be tilted. When the tilt angle is large or when the valve’s own weight is significant, support structures should be added to protect the valve. ⑶The pipeline in which electric control valves are installed generally does not need to be too high above the road surface or wooden floor; when the height of the pipeline exceeds 2 meters, a platform should be provided as much as possible to facilitate operator access and maintenance. ⑷Before installing the control valve, clean the pipeline by removing debris and weld defects. After installation, to ensure that no residues remain in the valve body, the gate valve should be cleaned again; that is, it is necessary to keep the entire gate valve open when materials are introduced, to prevent residues from getting stuck. After applying the handle tissue, it should be repaired to its original neutral position. ⑸To enable the self-acting control valve to allow the processing process to resume in the event of common failures or maintenance, a bypass valve pipeline must be installed on the control valve. It should also be noted whether the installation location of the electric control valve meets the requirements of the entire manufacturing process. ⑹The installation of some of the electrical components of self-acting control valves shall be carried out in accordance with the relevant construction regulations for electrical equipment projects. If it is an explosion-proof product, its installation shall be carried out in accordance with the \"Standards for the Installation of Electrical Equipment in Areas at Risk of Explosion\". If used on-site, the power transmission cables should be SBH-type or other six-core or eight-core cables with a rubber-coated outer layer and a diameter of around 11.3 mm. During maintenance, it is prohibited to connect power sources in flammable and explosive areas to open the gauge covers for maintenance, as well as to pry at the flameproof surfaces. Additionally, during disassembly, the flameproof surface must not be damaged or scratched, and it must be restored to its original flameproof condition after maintenance. ⑺After disassembling the reducer of an electric actuator, attention should be paid to lubrication with oil; low-speed motors generally do not require disassembly for lubrication. After the assembly line, it is also necessary to check whether the valve position matches the indicated opening degree of the valve. Single-seat control valves have low leakage rates, making it easy to achieve tight sealing and shut-off; for example, hard sealing between metals can be used, or soft sealing using metals in combination with polytetrafluoroethylene or other composite materials. The standard leakage rate is 0.01% C (where C is the rated flow coefficient). A low allowable pressure difference is permitted; for example, the allowable pressure difference for a DN100 valve is only 120 kPa. The flow capacity is low; for example, the flow capacity of a straight-through valve with DN100 is only 100. Due to the large thrust exerted by the fluid medium on the valve core, that is, the large unbalanced force, such control valves are not suitable for applications with high pressure differences and large diameters. In recent years, straight-through control valves with a cage structure have been widely used due to their advantages of simple maintenance and the ability to modify the valve’s flow characteristics by changing the valve seat. To reduce the impact of unbalanced forces on the valve spool, a high-thrust actuator can be used, a straight-through double-seat valve structure can be employed, or a valve cage structure with a balanced spool can be adopted. A sliding piston ring lubricated with graphite is used between the upper part of the spool and the cage cylinder body to provide sealing between the spool and the cage. Sealing is also achieved between the valve cage and the upper valve cover using valve cap gaskets, spiral gaskets, etc., to ensure that high-pressure fluid from the upstream side does not enter the low-pressure chamber on the downstream side. Furthermore, the fluid acts on both the bottom and top of the valve core through the balance connection holes at the top of the valve core, eliminating most of the static unbalance forces and providing a certain degree of damping to reduce the effects of disturbances such as vibrations caused by fluid flow. That’s all for today’s content. If there’s anything else you guys want to know, discuss, or even argue with me about, feel free to leave a comment below. Through wind and rain, I’ll be here waiting for you.