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Electric control valve is an important execution unit instrument in industrial automation process control. The structure is composed of an electric actuator and a regulating valve after being connected and combined by mechanical connection, assembly, debugging and installation to form an electric control valve. The electric control valve is the core instrument for adjusting the temperature and pressure of the medium in the pipeline, and its performance directly affects the safe operation of the entire system.   1. The Basic Structure Of Electric Control Valve The upper part of the electric control valve is the actuator, which accepts the 0~10mADC or 4~20mADC signal output by the regulator, converts it into the corresponding linear displacement, and pushes the lower control valve to act to directly adjust the flow of the fluid. The actuators of various types of electric control valves are basically the same, but the structure of the control valve (adjustment mechanism) is many types due to different conditions of use.   2. The Basic Structure Of Electric Actuator Its electric actuator is mainly composed of an isolated electrical part and a transmission part, and the motor is used as an intermediate part connecting the two isolated parts. The motor of the electric control valve outputs the torque according to the control requirements, and transmits it to the trapezoidal screw through the multi-stage spur gear, and the trapezoidal screw converts the torque into the thrust through the thread. The trapezoidal screw thus transmits the linear travel to the valve stem via the self-locking output shaft. The output shaft of the actuator has a non-rotating ring to prevent transmission, and the radial locking device of the output shaft can also be used as a moving position indicator. A flagpole is connected to the stop ring of the output shaft, the flagpole runs synchronously with the output shaft, and the displacement of the output shaft is converted into an electrical signal through the rack plate connected with the flagpole, which is provided to the intelligent control board as a comparison signal and valve position feedback output. At the same time, the stroke of the electric actuator can also be limited by the two main limit switches on the rack plate, and protected by two mechanical limits.   3. Working Principle Of Electric Actuator The compact electric actuator takes the electric motor as the driving source and the direct current as the control and feedback signal. When there is a signal input at the input end of the controller, the signal is compared with the position signal. When the deviation value of the two signals is greater than the specified dead zone, the controller generates power output and drives the servo motor to rotate to make the output shaft of the reducer Rotate in a direction to reduce this deviation until the deviation is less than the deadband. At this time, the output shaft is stabilized at the position corresponding to the input signal.   4. Controller Structure The controller consists of the main control circuit board, sensors, operating buttons with LEDs, split-phase capacitors, wiring terminals, etc. The intelligent servo amplifier is based on a dedicated single-chip microprocessor, and converts the analog signal and the valve position resistance signal into a digital signal through the input loop. The microprocessor displays the result and outputs the control signal after passing the artificial intelligence control software according to the sampling result.

The plug valve uses a plug with a through hole as a valve for the opening and closing parts. The cock rotates with the valve stem to realize the opening and closing action. Small unpacked plug valves are also known as "cocks". The plug of the plug valve is mostly a cone (also a cylinder). It cooperates with the conical hole surface of the valve body to form a sealing pair. The plug valve is the earliest type of valve. The plug valve has a simple structure, small external dimensions, fast opening and closing, and small fluid flow resistance, but the sealing surface is processed and maintenance is more difficult. The ordinary plug valve is sealed by the direct contact between the finished metal plug body and the valve body, so the sealing performance is poor, the opening and closing force is large, it requires a large rotating torque, and it is easy to wear. Usually only used for low pressure (<1MPa), small diameter (<100mm) and low temperature (<150 degrees Celsius). It is not suitable for high temperature. When the temperature changes greatly, it is easy to get stuck.   The Main Advantages Of The Plug Valve Are As Follows:   1. The plug valve is used for frequent operation, and it opens and closes quickly and easily. 2. The fluid resistance of the plug valve is small. 3. The plug valve is simple in structure, relatively small in size, light in weight, and easy to maintain. 4. Not limited by the installation direction, the flow direction of the medium can be arbitrary. 5. No vibration and low noise.   The plug valve, also known as the swivel door, is a quick-opening valve. According to its shunt situation, it is divided into straight-through type, three-way type, four-way type and so on. The straight-through type controls the flow of the medium on the straight pipe section, and the three-way type and the four-way type can be used to distribute the medium and change its flow direction. The working principle of the cock is that the cock body rotates around the center line of the valve body, and the purpose of opening and closing is achieved by the corresponding relationship between the port on the cock body and the ports at both ends of the valve body. The advantage of the cock is that it is easy to operate, open and close quickly, the resistance is small, the flow rate is large, the structure is simple, and the external dimension is small; The valve core may be deformed at high temperature and easily stuck at high temperature and high pressure.   The Plug Valve Is Often Used In The Following Pipelines:   The plug valve is mostly used for medium with lower temperature, and is often used in: 1. The pipeline needs to be fully opened and fully closed quickly. 2. Low pressure container liquid level indicator. 3. Places that are not frequently operated or used as inspections.

The opening and closing part of the ball valve is a sphere with a circular channel, which rotates around an axis perpendicular to the channel, and the sphere rotates with the valve stem to achieve the purpose of opening and closing the channel. The ball valve can be closed tightly with only a 90-degree rotation operation and a small torque. Different drive devices can be assembled to form ball valves with different control methods according to the needs of working conditions, such as electric ball valves, pneumatic ball valves, hydraulic ball valves and so on.   According to the structure can be divided into:   1. Floating Ball Valve   The ball of the ball valve is floating. Under the action of the medium pressure, the ball can produce a certain displacement and press tightly on the sealing surface of the outlet end to ensure the sealing of the outlet end.   The structure of the floating ball valve is simple and the sealing performance is good, but the load of the ball bearing the working medium is all transferred to the outlet sealing ring, so it is necessary to consider whether the sealing ring material can withstand the working load of the ball medium. This structure is widely used in medium and low pressure ball valves.   2. Fixed Ball Valve   The ball of the ball valve is fixed and does not move after being pressed. The fixed ball valve has a floating valve seat. After being pressurized by the medium, the valve seat moves, so that the sealing ring is tightly pressed on the ball to ensure the sealing. Bearings are usually installed on the upper and lower shafts with the ball, and the operating torque is small, which is suitable for high-pressure and large-diameter valves.   In order to reduce the operating torque of the ball valve and increase the availability of the seal, oil-sealed ball valves have appeared in recent years. Special lubricating oil is injected between the sealing surfaces to form an oil film, which not only enhances the sealing performance, but also reduces the operation. torque, more suitable for high-pressure and large-diameter ball valves.   3. Elastic Ball Valve   The ball of the ball valve is elastic. Both the ball and the valve seat sealing ring are made of metal materials, and the sealing specific pressure is very large. According to the pressure of the medium itself, the pressure cannot meet the sealing requirements, and external force must be applied. This valve is suitable for high temperature and high pressure medium.   The elastic sphere is obtained by opening an elastic groove at the lower end of the inner wall of the sphere to obtain elasticity. When the channel is closed, the wedge head of the valve stem is used to expand the ball and compress the valve seat to achieve sealing. Before turning the ball, loosen the wedge head, and the ball will return to its original shape, so that there is a small gap between the ball and the valve seat, which can reduce the friction and operating torque of the sealing surface.   Commonly used ball valve classification methods are as follows:   According to the size of the pressure: high pressure ball valve, medium pressure ball valve, low pressure ball valve   By flow channel type: full-bore ball valve, reduced-bore ball valve   By channel position: straight-through, three-way, right-angle   According to the temperature: high temperature ball valve, normal temperature ball valve, low temperature ball valve, ultra-low temperature ball valve   According to the sealing form: soft sealing ball valve, hard sealing ball valve   Assembly by stem: top entry ball valve, side entry ball valve   According to the connection form: flanged ball valve, welded ball valve, threaded ball valve, clamp ball valve   According to the driving method: manual ball valve, automatic control ball valve (pneumatic ball valve, electric ball valve, hydraulic ball valve)   By caliber size: super large diameter ball valve, large diameter ball valve, medium diameter ball valve, small diameter ball valve.

The biggest difference between the butterfly valve and the butterfly valve is that the opening and closing part of the butterfly valve is a plate, while the ball valve is a ball. Lifting motion; butterfly valve and gate valve can adjust the flow through the opening degree; ball valve is not convenient to do this.   1. The characteristics of ball valve and butterfly valve are different   Butterfly valve is characterized by fast opening and closing speed, simple structure and low cost, but its tightness and pressure bearing capacity are not good. The characteristics of the ball valve are similar to that of the gate valve, but due to the limitation of volume and opening and closing resistance, it is difficult to achieve a large diameter.   2. The structure principle of ball valve and butterfly valve is different   The structure principle of the butterfly valve is especially suitable for making the butterfly plate of the large-diameter valve butterfly valve installed in the diameter direction of the pipeline. In the cylindrical passage of the butterfly valve body, the disc-shaped butterfly plate rotates around the axis, and the rotation angle is between 0° and 90°. When it rotates to 90°, the valve is fully open. The structure is simple, the cost is low, and the adjustable range is large. Ball valves are usually suitable for liquids and gases without particles and impurities. The fluid pressure loss is small, the sealing performance is good, and the cost is high. In comparison, the sealing of ball valves is better than that of butterfly valves.     The ball valve seal depends on the valve seat being squeezed on the spherical surface for a long time. It must wear faster than the hemispherical valve. The seal of the ball valve is usually made of flexible materials, and it is difficult to use in high temperature and high pressure pipelines. Butterfly valve seal is mediated by rubber, which is far from the metal hard sealing performance of hemispherical valve, ball valve and gate valve. After long-term use of the hemispherical valve, the valve seat will also have a small amount of wear. It can continue to be used through adjustment. The valve stem and packing only need to rotate 90° during the opening and closing process. When there are signs of leakage, press the packing gland again. A few bolts can achieve no leakage at the packing, while other valves are still barely used for small leakage, and the valve is replaced with a large leakage.   In the process of opening and closing, the ball valve operates under the holding force of the valve seats at both ends. It has a larger opening and closing torque than the half-ball valve. The larger the nominal diameter, the more obvious the opening and closing torque difference. The opening and closing of the butterfly valve is to overcome the deformation of the rubber. To achieve, the torque is greater. The gate valve and globe valve operate for a long time and are laborious. Ball valve and plug valve are the same type of valve, only its closing part is a sphere, and the sphere rotates around the center line of the valve body to open and close a valve. Ball valves are mainly used to cut off, distribute and change the flow direction of the medium in the pipeline.   3. The application fields of ball valve and butterfly valve are different   At present, butterfly valve, as a component used to realize on-off and flow control of pipeline system, has been widely used in many fields such as petroleum, chemical industry, metallurgy, hydropower and so on. In the known butterfly valve technology, the sealing form mostly adopts the sealing structure, and the sealing material is rubber, polytetrafluoroethylene, etc. Due to the limitation of structural characteristics, it is not suitable for industries such as high temperature resistance, high pressure, corrosion resistance and wear resistance.   Ball valves can withstand high temperatures and pressures at relatively low cost. Therefore it is commonly used for water and gas applications. Due to their perfect durability and sealing properties, they provide excellent closing properties even after many years of use.

Introduction Of Installation Steps Of Stainless Steel Flanged Ball Valve When the valve is hoisted, the rope should not be tied to the handwheel or valve stem, so as not to damage these parts, it should be tied to the flange. Before installation, the valve should be checked to check the specifications and models to identify whether there is any damage, especially for the valve stem. Turn it a few times to see if it is skewed, because during transportation, the valve stem is most likely to be skewed. Also remove debris from the valve. When installing the stainless steel flanged ball valves , pay attention to tightening the bolts symmetrically and evenly. The valve flange and the pipe flange must be parallel with a reasonable gap to prevent the valve from generating excessive pressure or even cracking. Special attention should be paid to brittle materials and valves with low strength. Valves that must be welded to the pipe should be spot welded first, then the closing parts should be fully opened, and then welded to death. When installing the screw valve, the sealing packing should be wrapped on the pipe thread, and do not get into the valve, so as not to accumulate in the valve and affect the flow of the medium. The pipeline connected to the flanged ball valve must be cleaned. Compressed air can be used to blow away mud sand, iron oxide filings, welding slag and other debris. These debris not only easily scratch the sealing surface of the valve, but also block the small valve and make it invalid.   Advantages Of Stainless Steel Flanged Ball Valve The opening and closing is convenient and quick, labor-saving, small fluid resistance, and can be operated frequently. Simple structure, small size and light weight. The mud can be transported, and the liquid accumulation at the pipe mouth is the least. Good adjustment performance with professional flanged ball valve manufacturers . The fluid resistance is small, and the full-bore ball valve basically has no flow resistance. Tight and reliable. It has two sealing surfaces, and various plastics are widely used for the sealing surface materials of the ball valve at present, which has good sealing performance and can achieve complete sealing. It has also been widely used in vacuum systems. Easy to operate, quick to open and close, only need to rotate 90° from fully open to fully closed, which is convenient for long-distance control.

There are many types of gate valves, and knife gate valve is one of them, also called knife style gate valve. Depending on the type of structure, gate valves can be divided into flat gate valves and knife gate valves. According to the different connection methods, the knife gate valve can be divided into flange type, lug type and wafer type.   Compared with ordinary gate valve, the structure of knife gate valve is simple. It is small in size, flexible in operation and easy to install. It is more suitable for medium with high consistency and solid particles. As can be seen from the name, the knife gate valve mainly relies on the blade-shaped gate to cut off the medium. The gate has two sealing surfaces forming a wedge shape. The gate can be made into an integral rigid gate; it can also be made into an elastic gate that can produce a small amount of deformation and improve the sealing performance from the process. To sum up, the knife gate valve mainly highlights the following product advantages compared with ordinary gate valves:   The U-shaped gasket has a good sealing effect. The full diameter design makes the medium passing ability strong. At the same time, under the condition of dirty medium, it is easy to install, disassemble and maintain, and the sealing part of the valve can be replaced without removing the valve, which makes the maintenance of the valve easier. The gate with gate knife function has good gate breaking effect, can effectively cut off all kinds of sundries in the medium, and solve the leakage phenomenon after gate breaking of media containing blocks, particles and fibers. The ultra-short structure length of the knife gate valve, small size, small flow resistance, light weight, material saving and small effective space occupation.   Although the price of bonneted knife gate valve is higher than that of ordinary gate valve, its good performance has been generally recognized by the market.   The Scope Of Use Of The Knife Gate Valve: Mining, coal washing, iron and steel industry -- used for coal washing and washing pipelines, slag filtering pipelines, etc., ash discharge pipelines; Purification device - used for waste water, mud, dirt and clarified water with suspended solids; Paper industry - used for any concentration of pulp, material-water mixture; Power station ash removal - used for ash slurry.   Knife Gate Valve Installation Precautions Before installing the knife gate valve, check the valve cavity and sealing surface and other parts, and no dirt or sand is allowed to adhere. The bolts of each connecting part should be tightened evenly. Check that the packing parts are required to be pressed tightly, not only to ensure the sealing performance of the packing, but also to ensure the flexible opening of the gate; Before installing the valve, the user must check the valve model, connection size and pay attention to the flow direction of the medium to ensure the consistency with the valve requirements; When installing the valve, the user must reserve the necessary space for the valve drive; The wiring of the drive device must be carried out according to the circuit diagram; The knife gate valve must be maintained regularly, and must not be collided and squeezed at will, so as not to affect the sealing.

Butterfly valve, also known as flap valve, is often used in pipelines for conveying various corrosive and non-corrosive fluid media in engineering systems such as generators, coal gas, natural gas, liquefied petroleum gas, hot and cold air, chemical smelting, etc., for regulating and cutting off flow of the medium.   1. The working principle of butterfly valve   A butterfly valve is a valve that uses a circular butterfly plate as an opening and closing member and rotates with the valve stem to open, close and adjust the fluid channel. The butterfly plate of the butterfly valve is installed in the diameter direction of the pipeline. In the cylindrical channel of the butterfly valve body, the disc-shaped butterfly plate rotates around the axis, and the rotation angle is between 0° and 90°. When it rotates to 90°, the valve is in a fully open state. By changing the deflection angle of the disc, the flow of the medium can be controlled.   2. Four types of butterfly valves   (1) Concentric butterfly valve   The structural feature of this kind of butterfly valve is that the shaft center of the valve stem, the center of the butterfly plate and the center of the body are in the same position. The structure is simple and the manufacture is convenient. Common rubber-lined butterfly valves belong to this category. The disadvantage is that due to the fact that the butterfly plate and the valve seat are always in a state of extrusion and scraping, the resistance distance is large and the wear is fast.   (2) Single eccentric butterfly valve   In order to solve the extrusion problem of the disc and the valve seat of the concentric butterfly valve, the single eccentric butterfly valve was produced. Its structural feature is that the shaft center of the valve stem deviates from the center of the butterfly plate, so that the upper and lower ends of the butterfly plate no longer become the rotation axis, which disperses and reduces the excessive extrusion between the upper and lower ends of the butterfly plate and the valve seat.   (3) Double offset butterfly valve   On the basis of the single eccentric butterfly valve, the most widely used double offset butterfly valve is further improved and formed. Its structural feature is that the shaft center of the valve stem deviates from the center of the disc and the center of the body. The effect of double eccentricity enables the disc to break away from the valve seat immediately after the valve is opened, which greatly eliminates unnecessary excessive extrusion and scratching of the disc and the valve seat, reduces the opening resistance, reduces wear, and improves the performance of the valve. Seat life.   (4) Triple offset butterfly valve   To withstand high temperature, a hard seal must be used, but the amount of leakage is large; to zero leakage, a soft seal must be used, but it is not resistant to high temperature. In order to overcome the contradiction of the double offset butterfly valve, the butterfly valve has been eccentric for the third time (deviation from the center line of the metal sealing surface). The structure is characterized in that the conical axis of the sealing surface of the butterfly plate is deviated from the cylinder axis of the body while the position of the double eccentric valve stem is eccentric. That is to say, after the third eccentricity, the sealing section of the disc is no longer a true circle, but an ellipse. The biggest feature of the triple offset butterfly valve is that the sealing structure is fundamentally changed. It is no longer a position seal, but a torsion seal; it does not rely on the elastic deformation of the valve seat, but completely relies on the contact surface pressure of the valve seat to achieve the sealing effect.

The butterfly valve opening and closing part is a disc-shaped butterfly plate, which rotates around its own axis in the valve body, so that the valve that can open, close or adjust is called a butterfly valve. The butterfly valve is usually less than 90 degrees from fully open to fully closed. The butterfly valve and the butterfly stem have no self-locking ability. In order to locate the butterfly plate, a worm gear reducer should be installed on the valve stem. The use of worm gear reducer can not only make the butterfly plate have self-locking ability, so that the butterfly plate can stop at any position, but also improve the operation performance of the valve.   1. Features of high performance triple eccentric bidirectional hard sealing butterfly valve   The valve body and valve seat of the triple offset butterfly valve are connected components, and the sealing surface layer of the valve seat is surfacing with temperature-resistant and corrosion-resistant alloy materials. The multi-layer soft stacked sealing ring is fixed on the valve plate. Compared with the traditional butterfly valve, this butterfly valve has high temperature resistance, easy operation, and no friction when opening and closing. When closing, the torque of the transmission mechanism increases to compensate the sealing, which improves the butterfly valve. The advantages of excellent sealing performance and extended service life.   The valve seat sealing ring is composed of multi-layer stainless steel sheets on both sides of the soft T-shaped sealing ring. The sealing surface of the valve plate and the valve seat is an inclined conical structure, and the temperature and corrosion resistant alloy material is surfacing on the inclined conical surface of the valve plate; the spring fixed between the adjusting ring pressure plates and the adjusting bolts on the pressure plate are assembled together. This structure effectively compensates the tolerance zone between the shaft sleeve and the valve body and the elastic deformation of the valve stem under medium pressure, and solves the sealing problem of the valve during the two-way exchange of medium conveying. The sealing ring is composed of multi-layer stainless steel sheets on both sides of the soft T-shaped, which has the dual advantages of metal hard sealing and soft sealing, and has zero leakage sealing performance under low temperature and high temperature conditions.   2. Classification of butterfly valves   The types of butterfly valves can be divided into offset plate type butterfly valve, vertical plate type butterfly valve, inclined plate type butterfly valve and lever type butterfly valve according to the structure. According to the sealing form, it can be divided into two types: soft sealing butterfly valve and hard sealing butterfly valve. Soft-sealed butterfly valves are generally sealed with rubber rings, and hard-sealed butterfly valves are usually sealed with metal rings. According to the connection type, it can be divided into flange connection butterfly valve and wafer connection butterfly valve. According to the transmission mode, it can be divided into manual butterfly valve, gear transmission butterfly valve, pneumatic butterfly valve, hydraulic butterfly valve and electric butterfly valve.   3. Precautions for installation and maintenance of butterfly valves   (1) During installation, the valve disc should stop in the closed position.   (2) The opening position should be determined according to the rotation angle of the butterfly plate.   (3) For butterfly valves with bypass valves, the bypass valve should be opened before opening.   (4) It should be installed according to the manufacturer's installation instructions, and a firm foundation should be set for heavy butterfly valves.

The control valve consists of two main assemblies: valve body assembly and actuator assembly (or actuator system), which are divided into four series: single-seat series control valve, double-seat series control valve, sleeve series control valve and self-operated series control valve. Variations of the four types of valves can lead to many different applicable configurations, each with its own specific applications, features, advantages and disadvantages. While some control valves are used in a wider range of applications than others, control valves are not suitable for all applications to work together to create the best solution for enhanced performance and reduced cost.   1. Characteristics of control valve   (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 technological production process.   (2) Pneumatic control valves are divided into two types: air-on and air-off. The air-to-open control valve is closed in a fault state, and the air-to-close control valve is opened in a fault state. Some auxiliary equipment can be used to form a retaining valve or make the control valve self-locking, that is, the control valve maintains the valve opening before the failure when the fault occurs.   (3) The way of air opening and air closing can be realized by the combination of positive and negative actuator types and positive and negative valves. When using a valve positioner, it can also be realized by a valve positioner.   (4) Various control valves have different structures and have their own characteristics.   2. Type of control valve   There are many types of valve bodies for control valves. Common control valve types include straight-through single-seat, straight-through double-seat, angle, diaphragm, small flow, three-way, eccentric rotation, butterfly, sleeve, spherical, etc. When making specific choices, consider the following:   (1) It is mainly considered according to the selected flow characteristics and unbalanced force.   (2) When the fluid medium is a suspension containing a high concentration of abrasive particles, the internal material of the valve should be hard.   (3) Since the medium is corrosive, try to choose a valve with a simple structure.   (4) When the temperature and pressure of the medium are high and the change is large, the material of the valve core and the valve seat should be selected with a small change in temperature and pressure.   (5) Flash evaporation and cavitation only occur in liquid media. In the actual production process, flashing and cavitation will form vibration and noise, which will shorten the service life of the valve. Therefore, the valve should be prevented from flashing and cavitation when selecting the valve.   3. Application of control valve   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, and can be used as a circulating water supply control valve for atmospheric boilers. The valve is small in size, easy installation, high activation sensitivity, small head loss, no water hammer phenomenon, controlled by small floating balls can greatly improve the utilization rate of the water tower, for the newly built water tower, due to the reduction in the volume of the floating ball, the upper part of the water tower is left for the floating ball to float freely, and the required height is reduced to reduce the cost of the water tower to overcome the disadvantages of the old screw float valve, such as large size, easy damage, low working pressure, and a large amount of overflow.

Chemical valves are an important accessory for fluid control on industrial pipelines. Faced with various working conditions of complex industrial systems and a wide variety of valves, if you want to choose a suitable valve for the pipeline system, you should firstly understand the performance of the valve, and secondly, the steps and basis for selecting valves should be mastered. Third, the principles of selecting valves for petroleum and chemical industries should be followed.   Chemical valves not only have a wide range of applications, but also have a large amount of use. Of course, chemical valves have higher requirements than ordinary valves. The media generally used in chemical valves are relatively easy to corrode. From simple chlor-alkali industry to large petrochemical enterprises, there are high temperature, high pressure, corrosion resistance, wear resistance, and large temperature and pressure difference. For this kind of valve used in a more dangerous environment, it should be strictly implemented in accordance with chemical standards in the selection and use process. Geko flow control technology is a professional chemical valve manufacturer, and its products are manufactured in strict accordance with chemical standards.   1. How to choose chemical valve?   The chemical industry generally chooses a straight-through valve with a small flow resistance. It is usually used as a valve for closing and opening the medium. The valve that is easy to adjust the flow is used for controlling the flow. The plug valve and ball valve are more suitable for reversing and shunting. , the sliding of the closing member along the sealing surface with a wiping effect is most suitable for the medium with suspended particles. Common chemical valves include ball valves, gate valves, globe valves, safety valves, plug valves, check valves, etc. The mainstream of chemical valve media contains chemical substances, and there are many acid-base corrosive media. The manufacturers of chemical valve materials are mainly 304L and 316. For ordinary media, 304 is selected as the main material, and the corrosive fluids combined with various chemical substances are made of alloy steel or fluorine-lined.   2. The role of chemical valve types   (1) Open and close type: cut off or dredge the flow of fluid in the pipe.   (2) Adjustment type: adjust the flow and flow rate in the pipe.   (3) Throttling type: a large pressure drop occurs after the fluid passes through the valve.   (4) Other types: automatic opening and closing; maintaining a certain pressure; blocking steam and drainage.   3. Precautions before using chemical valves   (1) Whether there are blisters, cracks and other defects on the inner and outer surfaces of the chemical valve.   (2) Whether the connection between the valve seat and the valve body of the chemical valve is firm, whether the valve core and the valve seat match, and whether the sealing surface is defective.   (3) Whether the connection between the valve stem and the valve core of the chemical valve is flexible and reliable, whether the valve stem is bent, and whether the thread is damaged.

1. The function of the check valve is to ensure that the fluid flows in one direction   The moving parts usually press against the valve seat to form a seal. A small pressure must be applied to the moving parts to open the valve. Once opened, fluid power is generated to open or increase the valve opening. Fluid flow must stop before the valve will close. The fluid dynamics created by the fluid flow prevent all valves from closing. A spring may or may not be used to control the opening and assist in closing. Some check valves rely on gravity alone to provide the closing force. Valves that rely on gravity must be installed according to valve manufacturers' instructions. If horizontal pipes are specified, then the slope of a short distance local pipe must be changed.   Swing check valves are powered by gravity. As the valve opens, the force required to control the opening of the valve increases. If the balance between disc weight and fluid dynamic forces is incorrect, the valve will not fully open. Increasing the flow rate may cause unexpected corrosion or erosion damage, so gravity-driven valves must meet operating conditions.   When the valve is fully open, the disc or piston travel must be limited by a stop. A valve that is fully open, but not restrained, is susceptible to vibration. Vibration can cause rapid wear of the ammonium chain pins or piston. Valves using springs may experience early spring failure (caused by fatigue). Vibration may be caused by eddies or disturbances. When the fluid has some viscosity, fluid damping can restrain vibration. Valves using springs may be configured with springs of varying stiffness. This can be an effective vibration damper if the full travel stop includes squeezing to prevent rebound after a quick start.   2. The different designs of the check valve are to better play its role   Squeeze includes a seat and plate or piston design that prevents the check valve valve from slamming shut. The addition of extra material on the seat creates two squeeze areas. Try to squeeze fluid out of these areas, slowing down the valve during the snap shut. But there is a price to be paid for this. The increased area of limited clearance is an ideal site for collecting small solid particles. Controlled shut-off squeezing force protection can cause further problems due to collected solids unless there is a sufficient squeezing gap to eject the solids. Fragile solids such as coal may be crushed with a narrow seal. The squeeze area tends to expand the effective seat width and reduce the valve's ability to crush solids. This effect must be taken into account, taking into account all relevant solid properties. Ball valves often have very narrow seats and may scavenge solids for more efficient seating.   Vibration problems may be limited to small valves. When the valve is larger, the inertia of the moving parts increases. The increased inertia may effectively damp vibrations and result in a delayed shutdown after reverse flow has begun. Damping of the valve seat becomes very important. For all valves, the flow path area must be checked and flow rates calculated for design operating conditions. Disc and piston area are as important as primary orifice area. Smaller runner areas are susceptible to corrosion and cavitation wear can occur. For specific functions, the valve body of the check valve may include auxiliary connections, such as vents and drains. Valves for thermal applications may sometimes have a bypass valve to allow the system to warm up at low flow rates.

Ball valve and gate valve are the same type of valve, the difference is that its closing part is a sphere, and the sphere rotates around the center line of the valve body to achieve opening and closing. Ball valves are mainly used to cut off, distribute and change the flow direction of the medium in the pipeline.   Ⅰ. Flange ball valve, new type of valve that is widely used, has the following advantages:   1. The fluid resistance is small, and its resistance coefficient is equal to the pipe section of the same length.   2. Simple structure, small size and light weight.   3. Tight and reliable, the sealing surface material of the ball valve is widely used in plastic, and the sealing performance is good, and it has also been widely used in vacuum systems.   4. The Flange ball valve is easy to operate, opens and closes quickly, and only needs to rotate 90° from fully open to fully closed, which is convenient for long-distance control.   5. The maintenance is convenient, the ball valve has a simple structure, the sealing ring is generally movable, and it is more convenient to disassemble and replace.   6. When fully open or fully closed, the sealing surfaces of the ball and the valve seat are isolated from the medium, and when the medium passes through, it will not cause erosion of the valve sealing surface.   7. It has a wide range of applications, with a diameter ranging from a few millimeters to a few meters, and can be applied from high vacuum to high pressure. This type of valve should generally be installed horizontally in the pipeline.   Ⅱ. The working principle of flange ball valve   1. The opening process   (1) In the closed position, the ball is pressed against the valve seat by the mechanical pressure of the valve stem.   (2) When the handwheel is turned counterclockwise, the valve stem moves in the opposite direction, and the angular plane at the bottom makes the ball disengage from the valve seat.   (3) The valve stem continues to lift and interacts with the guide pin in the helical groove of the valve stem, so that the ball begins to rotate without friction.   (4) Until it reaches the fully open position, the flange ball valve stem is lifted to the limit position, and the ball rotates to the fully open position.   2. The closing process   (1) When closing, rotate the handwheel clockwise, the valve stem starts to descend and the ball leaves the valve seat and starts to rotate.   (2) Continue to rotate the handwheel, the valve stem is acted by the guide pin embedded in the upper spiral groove, so that the valve stem and the ball rotate 90° at the same time.   (3) When it is about to close, the ball has rotated 90° without contacting the valve seat.   (4) During the last few turns of the handwheel, the angular plane at the bottom of the valve stem is mechanically wedged to compress the ball, so that it is tightly pressed on the valve seat to achieve complete sealing.   The ball valve can be closed tightly with only a 90-degree rotation operation and a small torque. The completely equal valve body cavity provides a low resistance, straight-through flow path for the medium. It is generally believed that ball valves are most suitable for direct opening and closing, but recent developments have designed ball valves so that they can be used for throttling and flow control. The main feature of the flange ball valve is its compact structure, easy operation and maintenance, suitable for general working media such as water, solvent, acid and natural gas, but also suitable for media with harsh working conditions, such as oxygen, hydrogen peroxide, methane and ethylene. The ball valve body can be integral or combined.