How to choose valves for hydrometallurgical industry?

Stop valve: A stop valve refers to a valve in which the closing member (valve disc) moves along the centerline of the valve seat. According to this movement form of the valve disc, the change of the valve seat opening is proportional to the valve disc stroke. Since the opening or closing stroke of the valve stem of this type of valve is relatively short, and it has a very reliable shut-off function, and because the change of the valve seat opening is proportional to the stroke of the valve disc, it is very suitable for regulating flow. Therefore, this type of valve is very suitable for use as a cut-off or regulating as well as throttling. Once the globe valve disc is moved from the closed position, there is no contact between its valve seat and the valve disc sealing surface. Therefore, the mechanical wear of its sealing surface is very small, so its sealing performance is very good. The disadvantage is that particles in the flowing medium may be trapped between the sealing surfaces. However, if the valve disc is made into a steel ball or a porcelain ball, this problem will be solved. Since the valve seats and valve discs of most stop valves are relatively easy to repair or replace, and there is no need to disassemble the entire valve from the pipeline when repairing or replacing the sealing element, this is very suitable when the valve and pipeline are welded together. Due to the change in the flow direction of the medium through this type of valve, the minimum flow resistance of the globe valve is also higher than that of most other types of valves. However, this situation can be improved depending on the valve body structure and the layout of the valve stem relative to the inlet and outlet channels. At the same time, because the stop valve disc has a small stroke between opening and closing, and the sealing surface can withstand multiple openings and closings, it is very suitable for occasions that require frequent switching. Globe valves can be used in most media process systems. Various forms of stop valves have been developed to meet various uses in petrochemical, electric power, metallurgy, urban construction, chemical industry and other sectors. The use of stop valves is very common. However, due to the large opening and closing torque and long structural length, the nominal diameter is usually limited to less than 250mm, and some can reach 400mm. However, special attention must be paid to the inlet and outlet directions when selecting. Generally, the medium of stop valves below 150mm mostly flows from the bottom of the valve disc, while the medium of stop valves above 200mm mostly flows from the top of the valve disc. This is due to the closing torque of the valve. In order to reduce the opening or closing torque, generally stop valves above 200mm are equipped with internal or external bypass valves. The most obvious advantage of the stop valve is: During the opening and closing process, because the friction between the valve disc and the sealing surface of the valve body is smaller than that of the gate valve, it is wear-resistant. The opening height is generally only 1/4 of the valve seat channel diameter, so it is much smaller than the gate valve. Usually there is only one sealing surface on the valve body and valve disc, so the manufacturing process is relatively good and it is easy to maintain. However, the shortcomings of stop valves cannot be ignored. Its main disadvantage is that the overall flow resistance is relatively large, thus causing pressure loss, especially in hydraulic devices, this pressure loss is particularly obvious. Applicable occasions The application of stop valves is very wide, and stop valves are used in many occasions. However, depending on the different structural forms of the stop valve, the applicable occasions are also different. 1. Needle type stop valve is used for precise flow control. The valve disc is usually integrated with the valve stem. It has a very high-precision needle head that matches the valve seat. Moreover, the pitch of the stem thread of the needle type stop valve is thinner than that of the ordinary stop valve. Under normal circumstances, the size of the needle globe valve seat hole is smaller than the pipe size. Therefore, it is usually only applicable to pipelines with small nominal diameters, and is more commonly used for sampling valves. 2. DC stop valve The valve stem and channel of the DC stop valve are at a certain angle, and the valve seat sealing surface and the inlet and outlet channels are also at a certain angle. The valve body can be made integral or separate. The separate valve body type stop valve uses two valve bodies to sandwich the valve seat in the middle for easy maintenance. This type of stop valve allows the fluid to hardly change the flow direction, and has the smallest flow resistance among stop valves. The valve seat and valve disc sealing surface can be overlayed with hard alloy to make the entire valve more resistant to erosion and corrosion. It is very suitable for pipeline control in the alumina production process, and is also suitable for pipelines with coking and solid particles. 3. Angle-type stop valve The biggest advantage of the angle-type stop valve is that the valve can be installed at the corner of the pipeline system, which not only saves 90° elbows, but also facilitates operation. Therefore, this type of valve is most suitable for use in ammonia production systems and refrigeration systems in fertilizer plants. For example, J44H-160, J44H-320, L44H-160, and L44H-320 are completely designed for synthetic ammonia production systems. 4. Steel ball or porcelain ball sealed globe valve. The structural characteristics of this valve are that the valve body is divided into one-piece and split types, and the valve disc is made of STL cemented carbide steel ball or porcelain ball made of amorphous material through powder molding, high-temperature sintering and precision research. The lower end of the valve stem rolls and envelops the ball in the ball hole of the valve stem. When the ball rotates three-dimensionally in the ball hole of the valve stem, it can produce countless sealing lines. * * It increases the service life of the sealing surface and ensures reliable sealing. Due to the limitation of the ball seal, this valve is generally used for smaller nominal diameters, about 6 to 25 mm. The valve is suitable for high-temperature and high-pressure steam pipelines in nuclear power plants and thermal power plants, instrument pipelines in sampling and sewage systems, and temperature-resistant, pressure-resistant, wear-resistant, and corrosion-resistant pipelines in petrochemical and chemical systems. 5. High-temperature and high-pressure power station stop valve. The structural characteristics of this valve are that the connection between the valve body and the valve cover adopts a pressure self-tightening sealing type or a clamp type. The connection between the valve body and the pipeline is a butt welding connection. The valve body material is mostly chromium-molybdenum steel or chromium-molybdenum-vanadium steel, and the sealing surface is mostly surfacing with hard alloy. Therefore, this type of valve can withstand high temperatures and pressures and has good heat resistance. ； The sealing surface is wear-resistant, scratch-resistant and corrosion-resistant, with good sealing performance and long service life. It is most suitable for pipelines of high-temperature and high-pressure sleep, steam, oil, and superheated steam in thermal power industrial systems, petrochemical systems, and metallurgy. 6. API stop valve This type of stop valve is designed in strict compliance with the ASME B16.34 standard. ； The connection between the valve body and the valve cover, the installation of the stuffing box, the stem nut, and the upper seal are all designed in strict accordance with API600. Valve material selection fully complies with API600 requirements. Structural length complies with ASME B16.10 ； Flange connection dimensions comply with ANSI/ASMEB16.5a. Valve inspection and testing are strictly carried out in accordance with API598. Therefore, this valve is widely used in petrochemical pipelines, as well as in electric power, metallurgy, textile and other systems. 7. Stop valve for oxygen pipeline. This valve is designed strictly according to the requirements of oxygen pipeline. The stuffing box part is strictly sealed, and external dirt must not enter the stuffing box. The flanges at both ends of the valve body are equipped with grounding devices. After installation on the pipeline, they should be grounded to prevent static electricity fires. The shell material of this valve is austenitic stainless steel or copper, which has good electrical conductivity and is not prone to static electricity fire. The sealing material is polytetrafluoroethylene and the valve body material is a soft seal with good sealing performance and zero gas leakage. This valve is strictly degreased with carbon tetrachloride before assembly. It is absolutely free of grease and dirt and will not cause static fire. This valve is suitable for oxygen pipelines in metallurgical systems and is also suitable for oxygen pipelines in other industries. 8. Petroleum liquefied gas stop valve This valve is specially designed for petroleum liquefied gas pipelines or devices. Attention was paid to fire protection requirements on the structure. The packing is made of polytetrafluoroethylene, which ensures reliable sealing and ensures no material leakage. The secondary sealing material is made of polytetrafluoroethylene or nylon as opposed to the valve body material, which is a soft seal and ensures reliable sealing. This valve is suitable for liquefied petroleum gas pipeline systems. As an opening and closing device, it is also suitable for other pipelines with temperatures ≤80°C. 9. Threaded stem stop valve The stem of this type of stop valve is not in direct contact with the working medium. Depending on the shell material, sealing material, packing material and valve stem material, it is suitable for different working conditions. If the valve body and valve cover are made of carbon steel, the sealing material is alloy steel, the packing is flexible graphite, and the valve stem material is Cr13 stainless steel, it is suitable for water, steam, and oil pipelines. ； If the material of the valve body and valve cover is 1Cr18Ni9 or 0Cr18Ni9, the sealing material is the valve body itself or cemented carbide, the filler is polytetrafluoroethylene, and the valve stem material is Cr17Ni2, it is suitable for nitric acid-based corrosive medium pipelines or devices. ； If the valve body and valve cover material is 1Cr18Ni12Mo2Ti or 0Cr18Ni12Mo2Ti, the sealing material is the valve body itself or cemented carbide, the filler is polytetrafluoroethylene, and the valve stem material is 1Cr18Ni12Mo2Ti, it is suitable for acetic acid-based corrosive medium pipelines or devices. However, the maximum nominal diameter of this type of stop valve is 200mm. Stop valves above 200mm must be equipped with a bypass valve or an internal bypass structure in the design. Generally, the inlet end of the stop valve with DN ≥ 200mm is above the valve disc, that is, high in and low out. This is to prevent too much effort when closing and the valve stem is too thick. 10. The thread of the stem of this type of stop valve is in direct contact with the working medium and is directly corroded by the medium, making the stem thread easy to rust and causing difficulty in opening and closing. The nominal diameter of stop valves with this kind of structure is relatively small, generally between 6 and 50mm. Most of them are used in instrument valves and sampling valves. 11. API602 forged steel stop valve This type of stop valve is designed according to the American Petroleum Institute standard API602. The valve body and bonnet are forged from carbon steel or stainless steel. The valve body and bonnet are connected by bolts, threaded connections and welding. There are upper threaded valve stems and lower threaded valve stems. The sealing material is Cr13 steel, stainless steel, acid steel or STL. Carbide, the filler is flexible graphite or polytetrafluoroethylene, the connection methods include flange, thread, socket welding and butt welding, the pressure level is CL150 ~ CL1500, and the nominal diameter is 1/4 ~ 2in. It is widely used in installations and pipelines in petrochemical, electric power, chemical and other departments. The working medium is steam, oil and corrosive media. The structural length is in accordance with ASMEB16.10, the flange connection dimensions are in accordance with ASME/ANSI B16.5a, the welding end dimensions are in compliance with ASME B16.25, the socket welding hole dimensions are in compliance with ANSI B16.11, and the threaded connection end dimensions are in compliance with ANSI B1.20.1. 12. Plunger stop valve This type of plunger valve has a radial seal, which is achieved by two elastic sealing rings placed on a polished plunger. The two elastic sealing rings are separated by a collar, and the load exerted on the valve cover through the connecting bolts between the valve body and the valve cover presses the elastic sealing ring around the plunger firmly to ensure sealing. The material combination of this valve is carbon steel for the shell, Cr13 stainless steel for the plunger, and flexible graphite for the sealing ring. It can be used for water, steam, and oil pipelines. ； If the shell is made of stainless acid-resistant steel, the plunger is made of stainless acid-resistant steel, and the sealing ring is made of polytetrafluoroethylene, it is suitable for acid and alkali corrosive media. The advantages of this valve are reliable sealing, long life and easy maintenance. ； The disadvantage is that the opening and closing speed is slow. This type of valve is widely used in urban construction systems and water and steam pipelines in urban heating. Applicable Principles Globe valves are one of the most widely used valves. With the development of ball valves and butterfly valves, some of the applications of globe valves have been replaced. However, judging from the characteristics of the globe valve itself, ball valves and butterfly valves cannot be replaced. The selection principle is: 1. Stop valves should be used on pipelines or devices with high temperature and high pressure media. Such as thermal power plants, nuclear power plants, and petrochemical systems, it is appropriate to use stop valves on high-temperature and high-pressure pipelines. 2. On pipelines where flow resistance requirements are not strict. That is, pressure loss is not considered a big concern. 3. Stop valves can be used for small valves, such as needle valves, instrument valves, sampling valves, pressure gauge valves, etc. 4. There is flow adjustment or pressure adjustment, but the adjustment accuracy is not high, and the pipeline diameter is relatively small. For example, on pipelines with a nominal diameter of ≤50mm, a stop valve or a throttle valve should be used. 5. For small and large fertilizers in synthetic industrial production, high-pressure angle stop valves or high-pressure angle throttle valves with nominal pressures of PN160 and 16MPa or PN320 and 32MPa should be used. 6. In the desiliconization workshop and pipelines prone to coking in alumina Bayer process production, it is easy to choose DC stop valves or DC throttle valves with separate valve bodies, removable valve seats, and carbide sealing pairs. 7. In water supply and heating projects in urban construction, stop valves, balance valves or plunger valves can be used for pipelines with a smaller nominal diameter, such as pipelines with a nominal diameter less than 150mm.

The ball valve and the plug valve belong to the same type of valve, only its closing part is a ball, and the ball rotates around the center line of the valve body to open and close. Ball valves are mainly used in pipelines to cut off, distribute and change the flow direction of media. Ball valve is a new type of valve that has been widely used in recent years. It has the following advantages: 1． The fluid resistance is small, and its resistance coefficient is equal to that of a pipe section of the same length. 2． It has simple structure, small size and light weight. 3． Tight and reliable, plastic is widely used as the sealing surface material of ball valves at present, with good sealing performance, and has also been widely used in vacuum systems. 4． It is easy to operate and opens and closes quickly. It only needs to be rotated 90° from fully open to fully closed, which is convenient for long-distance control. 5. It is easy to maintain. The ball valve has a simple structure and the sealing ring is generally movable, making it easy to disassemble and replace. 6. When fully open or fully closed, the sealing surfaces of the ball and valve seat are isolated from the medium. When the medium passes, it will not cause erosion of the valve sealing surface. 7. It has a wide range of applications, with diameters ranging from a few millimeters to several meters, and can be applied from high vacuum to high pressure. Ball valves have been widely used in petroleum, chemical industry, power generation, papermaking, atomic energy, aviation, rocket and other departments, as well as in people's daily life. Ball valves can be divided according to structural form: 1. Floating ball ball valve The ball of the ball valve is floating. Under the action of medium pressure, the ball can produce a certain displacement and press against the sealing surface of the outlet end to ensure the sealing of the outlet end. The floating ball valve has a simple structure and good sealing performance, but all the load of the working medium on the ball is transferred to the outlet sealing ring. Therefore, 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 ball valve The ball of the ball valve is fixed and does not move after being pressed. Fixed ball and ball valves all have floating valve seats. After being subjected to medium pressure, the valve seat moves, causing the sealing ring to press tightly on the ball to ensure sealing. Bearings are usually installed on the upper and lower shafts of the ball, with small operating torque, and are suitable for high-pressure and large-diameter valves. As shown in Figure 2-6. In order to reduce the operating torque of the ball valve and increase the reliability 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 enhances the sealing and reduces the operating torque. It is more suitable for high-pressure and large-diameter ball valves. 3. Elastic ball valve The ball of the ball valve is elastic. The ball and valve seat sealing ring are both made of metal materials, and the sealing specific pressure is very large. The pressure of the medium itself cannot meet the sealing requirements, and external force must be applied. This kind of valve is suitable for high temperature and high pressure media. The elastic sphere obtains elasticity by opening an elastic groove at the lower end of the inner wall of the sphere. When closing the channel, use the wedge-shaped head of the valve stem to expand the ball and compress the valve seat to achieve a seal. Loosen the wedge-shaped head before turning the ball, and the ball will return to its original shape, leaving a small gap between the ball and the valve seat, which can reduce friction on the sealing surface and operating torque. Ball valves can be divided into straight-through type, three-way type and right-angle type according to their channel position. The latter two ball valves are used to distribute media and change the flow direction of media.

A valve in which the butterfly plate rotates around a fixed axis in the valve body is called a butterfly valve. 1. As a sealed butterfly valve, it developed rapidly after the emergence of synthetic rubber, so it is a new type of shut-off valve. In our country until the 1980s, butterfly valves were mainly used as low-pressure valves, and the valve seats were made of synthetic rubber. By the 1990s, due to the increase in foreign exchanges, hard-sealed (metal-sealed) butterfly valves developed rapidly. At present, there are many valve factories that can stably produce medium-pressure metal-sealed butterfly valves, making butterfly valves applicable to a wider range of fields. 2. The media that butterfly valves can transport and control include water, condensate, circulating water, sewage, sea water, air, gas, liquid natural gas, dry powder, mud, pulp and mixtures with suspended solids. The current parameters of domestically produced butterfly valves are as follows:: Nominal pressure: PN0.25——4.0MPa nominal diameter: DN100——3000mm working temperature: ≤425℃ 3.Butterfly valve types: According to the connection method: Flange type, clamp type. According to the sealing surface material ； Soft seal, hard seal. According to the structural form, butterfly valves can be divided into the following types: ——Plate butterfly valve - inclined plate type - offset plate type - lever type 4. Characteristics of butterfly valve: (1) Simple structure and small size. Due to its compact structure, short structural length, small size and light weight, it is suitable for large-diameter valves. (2) The fluid resistance is small. When fully open, the effective circulation area of ​​the valve seat channel is large, so the fluid resistance is small. (3) Opening and closing are convenient and fast, and the adjustment performance is good. The butterfly plate can be opened and closed by rotating 90°. By changing the rotation angle of the butterfly plate, the flow rate can be controlled in stages. (4) The opening and closing torque is small. Since the butterfly plates on both sides of the rotating shaft are basically equally affected by the medium and the torque is generated in opposite directions, opening and closing is less labor-intensive. (5) The low-pressure sealing performance is good. The sealing surface materials are generally made of rubber and plastic, so the sealing performance is good. Limited by the material of the sealing ring, the operating pressure and operating temperature range of the butterfly valve is small. However, the operating pressure and operating temperature range of hard-sealed butterfly valves have been greatly improved. 5. Structure of butterfly valve Butterfly valve is mainly composed of valve body, butterfly plate, valve stem, sealing ring and transmission device. The structure of the butterfly valve is shown in Figure 1-21. (1) Valve body The valve body is cylindrical, with a cylindrical boss on the upper and lower parts for installing the valve stem. Butterfly valves and pipelines are often connected by flanges ； If clamp connection is used, the structural length is the smallest. (2) Valve stem The valve stem is the rotating shaft of the butterfly plate. The end of the shaft adopts a stuffing box sealing structure to prevent medium leakage. The upper end of the valve stem is directly connected to the transmission device to transmit torque. (3) Butterfly plate The butterfly plate is the opening and closing part of the butterfly valve. According to the installation method of the butterfly plate in the valve body, butterfly valves can be divided into the following forms:: ①Centrally symmetrical plate. The valve stem is fixed on the radial center hole of the butterfly plate, and the valve stem and butterfly plate are installed vertically. 2. Non-sealed butterfly valve: A butterfly valve that cannot guarantee a seal when closed. It can only be used for throttling in the pipeline, and the sealing ring is usually made of metal.

Gate valve refers to a valve in which the closing member (gate plate) moves in the vertical direction along the center line of the passage. The gate valve can only be used for fully opening and fully closing in the pipeline, and cannot be adjusted or throttled. Gate valve is a kind of valve with a wide range of uses. It is generally used for cutting devices with a diameter of DN ≥ 50mm. Sometimes gate valves are also used for cutting devices with very small diameters. The gate has two sealing surfaces. The two sealing surfaces of the most commonly used mode gate valve form a wedge shape. The wedge angle varies with the valve parameters, usually 50, and 2°52' when the medium temperature is not high. The gate plate of the wedge gate valve can be made into a whole, which is called a rigid gate plate. ； It can also be made into a gate that can produce slight deformation to improve its processability and compensate for the deviation of the sealing surface angle during the processing. This type of gate is called an elastic gate. 　　When the gate valve is closed, the sealing surface can be sealed only by the medium pressure, that is, the medium pressure is used to press the sealing surface of the gate plate to the valve seat on the other side to ensure the sealing surface sealing, which is self-sealing. Most gate valves adopt forced sealing, that is, when the valve is closed, external force must be relied on to force the gate plate to the valve seat to ensure the sealing performance of the sealing surface. 　　The gate plate of the gate valve moves linearly with the valve stem, which is called a lifting stem gate valve (also called a rising stem gate valve). Usually there is a trapezoidal thread on the lift rod, and through the nut on the top of the valve and the guide groove on the valve body, the rotational motion is changed into linear motion, that is, the operating torque is changed into the operating thrust. 　　When the valve is opened, when the lift height of the gate plate is equal to 1:1 times of the valve diameter, the fluid channel is completely unobstructed, but during operation, this position cannot be monitored. In actual use, the top of the valve stem is used as a mark, that is, the position that does not open, as its fully open position. In order to consider the locking phenomenon caused by temperature changes, the valve is usually opened to the top position and then retracted 1/2-1 turn as the fully open valve position. Therefore, the fully open position of the valve is determined by the position of the gate (i.e. stroke). Advantages of the gate valve: (1) Small fluid resistance. Because the internal medium channel of the gate valve body is straight, the medium does not change its flow direction when flowing through the gate valve, so the fluid resistance is small. (2) The opening and closing torque is small, and the opening and closing of the gate valve requires less effort because the gate plate movement direction is perpendicular to the direction of medium flow when the gate valve opens and closes. Compared with the stop valve, the opening and closing of the gate valve requires less effort. (3) The flow direction of the medium is not restricted. The medium can flow in any direction from both sides of the gate valve without disturbing the flow or reducing the pressure, and the purpose of use can be achieved. It is more suitable for pipelines where the flow direction of the medium may change. (4) The structural length is shorter because the gate plate of the gate valve is placed vertically in the valve body, while the disc of the stop valve is placed horizontally in the valve body, so the structural length is shorter than that of the stop valve. (5) The sealing performance is good and the sealing surface is less eroded when fully open. (6) When fully open, the sealing surface is less eroded by the working medium than the stop valve. (7) The body shape is relatively simple, the casting process is good, and the application range is wide. Disadvantages of the gate valve: (1) The sealing surface is easy to damage. When opening and closing, the gate plate and the valve seat are in contact with each other, and there is relative friction between the two seals, which is easy to damage, affecting the performance and service life of the seal, and making maintenance difficult. (2) The opening and closing time is long and the height is large. Since the gate valve must be fully open or fully closed when opening and closing, the gate has a large stroke and requires a certain space for opening. The outer dimensions are high and the space required for installation is large. (3) Gate valves with complex structures generally have two sealing surfaces, which requires more processing, grinding and maintenance. There are more difficult parts, making manufacturing and maintenance more difficult, and the cost is higher than that of stop valves. Diameter shrinkage of gate valve: If the diameter of the channel in a valve body is different (often the diameter at the valve seat is smaller than the diameter at the flange connection), it is called diameter shrinkage. Diameter shrinkage can reduce the size of parts, correspondingly reduce the force required for opening and closing, and at the same time expand the application range of parts. But after the diameter shrinks. Fluid resistance loss increases. Under certain working conditions in some sectors (such as oil pipelines in the petroleum sector), valves with reduced diameter are not allowed. On the one hand, this is to reduce the resistance loss of the pipeline, and on the other hand, it is to prevent the diameter shrinkage from causing obstacles to the mechanical cleaning pipeline.

Diaphragm valve is a special form of cut-off valve that appeared in the 1920s. Its opening and closing part is a diaphragm made of soft material, which separates the inner cavity of the valve body from the inner cavity of the valve cover and the driving components, so it is called a diaphragm valve. Characteristics of the diaphragm valve: The most prominent feature is that the diaphragm separates the lower valve body cavity from the upper valve cover cavity, so that the valve stem, valve disc and other parts located above the diaphragm are not corroded by the medium, eliminating the need for a packing sealing structure, and no medium leakage occurs. Diaphragms made of soft seals such as rubber or plastic have better sealing properties. Since the diaphragm is a wearing part, it should be replaced regularly depending on the characteristics of the medium. Limited by the diaphragm material, diaphragm valves are suitable for situations with low pressure and relatively low temperature. Diaphragm valves can be divided into: Six types: house type, DC type, cut-off type, straight-through type, gate type and right-angle type ； The connection form is usually flange connection ； According to the driving mode, it can be divided into three types: manual, electric and pneumatic. Among them, pneumatic drive is divided into three types: normally open, normally closed and reciprocating.

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