Explanation of various valves

There are many types of valves and a wide range of applications. Sometimes it is the main equipment in the pipeline and plays a controlling role; sometimes it is a secondary equipment and plays an auxiliary role. If used improperly, the phenomenon of “running, emitting, dripping, and leaking” will occur, which may affect production, and cause accidents in severe cases. Therefore, understanding and correct use of valves is a very important issue. 1 Valve classification In the heating system, there are many kinds of valves used. Such as gate valve, globe valve, ball valve, butterfly valve, check valve, safety valve, regulating valve, balance valve, self-operated balance valve and so on. Introduce one by one below.

1.1 Gate valve Also called gate valve, gate valve, is a widely used valve. Working principle: The sealing surface of the gate and the sealing surface of the valve seat are highly smooth, flat and consistent, and processed into a very close and tight sealing pair. The gate plate conducts and shuts off the medium through the upward and downward pressure of the valve stem. It plays a shut-off role in the pipeline. Advantages: fluid resistance is small; the sealing surface is not eroded when fully opened; it can be used in the case of two-way flow of the medium without directionality; it is strong and durable; it is not only suitable for small valves, but also large valves. Disadvantages: high height; long opening and closing time; cumbersome; difficult to repair; if it is a large-diameter gate valve, manual operation is more laborious. According to the different valve stems, the gate valve can be divided into clear rod type and concealed rod type; according to the different gate structure, it is divided into parallel type and wedge type; there are also single gate and double gate. In heating engineering, the common used are the exposed rod wedge single gate valve (Z41H-16C) and the concealed rod wedge single gate valve (Z45T-10). The former is installed on the primary side of the heating station, and the latter is installed in the heating station. The secondary side. It generally plays two roles: as the main equipment as a switch; as an auxiliary equipment installed before and after the main equipment for maintenance.

When installing the gate valve, do not place the handwheel below the horizontal line (upside down), otherwise the medium will remain in the valve cover for a long time, which will easily corrode the valve stem. In heating engineering, gate valves were once the main force in valves. Now with the widespread adoption of butterfly valves, gate valves have been replaced by butterfly valves. 1.2 The stop valve is also a widely used valve. Generally the caliber is below 100 mm. Its working principle is similar to that of a gate valve, except that the closing part (disc) moves along the center line of the valve seat. It has a shut-off function in the pipeline and can also roughly adjust the flow rate. Advantages: easy to manufacture, convenient to maintain, strong and durable. shortcoming: Only allow the medium to flow in one direction, and have directionality during installation. The flow resistance is large, and the sealing performance is poor. According to different structures, it can be divided into straight-through type, right-angle type, DC type and balanced type. The flange straight-through type (J41H) and internal thread straight-through type (J11H) are generally used in engineering. The stop valve is directional and cannot be reversed. It’s not suitable to fall in peace. In our production and life, the straight-through, small-diameter globe valves used in the past have been gradually replaced by ball valves. 1.3 Ball valve Compared with gate valve and stop valve, ball valve is a new type of valve that is gradually being widely used. Its working principle is: the valve core is a ball with a through cavity, and the valve core is controlled to rotate 90° through the valve stem to make the valve unblocked or blocked. It plays a shut-off role in the pipeline. Advantages: In addition to the advantages of gate valves and stop valves, it also has the advantages of small size, good sealing (zero leakage), and easy operation. At present, it is widely used in petrochemical, electric power, nuclear energy, aviation, aerospace and other sectors. Disadvantages: difficult to maintain.

There are two types of ball valves: floating ball type and fixed ball type. In the heating project, some key locations, such as important branches and the connection population of heating stations, below DN250, often use imported ball valves. It has a different structure from domestic ball valves: the body of domestic ball valves is generally two-piece or three-piece, with flange connection; while the valve body of imported ball valve is one-piece, welded and connected, and there are fewer failure points. Its origin is northern Europe, such as Finland, Denmark and other countries with relatively developed heating technology. Such as Finland’s NAVAL, VEXVE, Denmark’s DAFOSS and so on. Because of its excellent sealing and operational reliability, it has been favored by users for a long time. The ball valve has no directionality and can be installed at any angle. When the welding ball valve is installed horizontally, the valve must be opened to prevent the electric spark from welding on the surface of the ball; when installing on a vertical pipeline, if the upper interface is welded, the valve must be opened, if the lower interface is welded, the valve must be closed to avoid the inside of the valve Burned by high heat. 1.4 Butterfly valve In the heating system, it is currently the most widely used valve with the most types. Working principle: The valve disc is a disc. Through the rotation of the valve stem, the valve disc rotates at 90°C within the range of the valve seat to realize the opening and closing of the valve. It plays a shut-off role in the pipeline. The flow can also be adjusted. Advantages: simple structure, light volume, convenient operation and good airtightness. Disadvantages: When fully open, the valve plate (sealing ring) is eroded by the medium. In the heating project, the butterfly valves used include three-eccentric metal sealing butterfly valves and rubber soft sealing butterfly valves. 1.4. 1 Triple eccentric metal seal butterfly valve The so-called “triple eccentric” refers to the deviation of the relative position of the valve shaft and valve plate in the valve. Ordinary butterfly valves are all eccentric, that is, the center line of the valve shaft is deviated from the center line of the sealing surface (the center line of the valve plate); for high performance, an eccentricity is added, that is, the center line of the valve shaft is deviated from the center line of the valve (the center line of the pipeline); The purpose of the double eccentricity is to make the valve plate open to 20°, the sealing pair will be separated from each other, thereby reducing friction (cam effect). The triple eccentric butterfly valve adds a unique eccentricity on the basis of the above double eccentricity-oblique cone, that is, the offset of the valve plate (the sealing surface is inclined at an angle with the vertical surface of the pipeline).

In this way, the valve is completely separated from the sealing pair within the 90° stroke range, which not only strengthens the cam effect, but also completely eliminates the friction; at the same time, when the valve is closed, when the sealing pair is gradually closed, a “wedge effect” is generated, with a minimum Torque achieves the tightest shut-off. The so-called “metal seal” means that the valve seat and sealing ring are made of high-quality alloys that are wear-resistant, corrosion-resistant and high-temperature resistant; at the same time, in order to prevent the sealing ring and the valve seat from being hard hit, the sealing pair is designed to be in flexible contact, that is, to form “elasticity”. “Metal seal” to ensure tight closing and no friction when opening. With the “three eccentric” structure, supplemented by the “elastic metal seal”, such a valve is easy to operate, durable and well sealed. The triple eccentric metal sealing butterfly valve is generally used on the main line and main branch of the heating system. The caliber is above DN300. Imported triple eccentric metal sealing butterfly valve has no directionality, but generally there is a suggested installation direction, and it is not suitable to install it in reverse; domestically produced has directionality, generally the reverse direction is one leakage level or one or two pressure levels worse than the forward direction, and it cannot be installed reversely. If welding on a horizontal pipeline, the valve should be closed to protect the sealing ring; if welding on a vertical pipeline, the valve should be closed, and water should be poured on the valve plate to extinguish welding slag during welding. When installing on a horizontal pipeline, it is recommended that the valve stem is horizontal or inclined to a certain vertical direction to ensure the cleanliness of the bottom bearing. 1.4.2 Rubber soft sealing butterfly valve The butterfly plate is generally electroplated ductile iron, and the sealing ring is rubber material. Different sealing materials have different performances.

Commonly used are: Dingqing rubber, applicable temperature-12 ℃-+82 ℃; ethylene propylene rubber, applicable temperature-45 ℃-+135 ℃; heat-resistant ethylene propylene rubber, applicable temperature-20 ℃-+150 ℃. Commonly used in heating engineering are wafer type (D371X) and flange type (D341X). Handle drive below DN125 (D71, D41X). Wafer butterfly valve is small and light, open and close quickly, easy to operate, easy to install, easy to maintain, good sealing and adjustment performance, high cost performance, so it should be used vigorously. The soft sealing butterfly valve has no directionality and can be installed arbitrarily. When the butterfly valve is in storage, the valve plate should be opened 4°-5°. In order to avoid long-term pressure and deformation of the sealing ring, which affects the sealing. 1.5 Check valve Also called check valve, single flow door. A commonly used auxiliary valve. Working principle: The valve is automatically opened and closed according to the strength of the fluid itself and the weight of the valve disc. As the name implies, its function is to prevent the medium from flowing back. It is generally installed at the outlet of the water pump to prevent damage to the water pump caused by water hammer. Commonly used in heating engineering are the horizontal lift type (H41H), the single flap swing type (H44H), and the double flap butterfly type (H77H). The check valve is directional and must not be reversed. Different types of check valves have a fixed installation method according to their structure, and they must not be installed incorrectly. The horizontal lift type can only be installed on the horizontal pipeline, and the valve flap is in a vertical state; the single flap swing type can only be installed on the horizontal pipeline, and the valve rotation axis is guaranteed to be in a horizontal state; the double flap butterfly type can be installed arbitrarily. 1.6 Regulating valve Also called throttle valve. It is a commonly used valve in the secondary network of the heating system. Working principle: The shape and structure are similar to the globe valve. Only the sealing pair is different. The valve flap and valve seat of the regulating valve are similar to the stopper and bottle mouth of a thermos bottle, and the flow area is adjusted by the movement of the valve flap. There is a scale on the valve shaft to indicate the corresponding flow. Function: Adjust the medium flow distribution between pipelines to achieve thermal balance. The straight-through type (T41H) was used in heating projects, but it has some shortcomings: the flow resistance is large and it is not suitable for vertical installation. So with the advancement of technology, the balance valve (PH45F) replaced the regulating valve. 1.7 Balance valve Improved control valve. The flow channel adopts direct flow, and the valve seat is changed to polytetrafluoroethylene; it overcomes the shortcomings of large flow resistance and adds two advantages at the same time: more reasonable sealing and cut-off function. It is used on the secondary network of the heating station in the heating project, with excellent flow regulation characteristics, especially suitable for variable flow systems. It is directional and can be installed horizontally or vertically. 1.8 Self-operated balancing valve is also called flow control valve. How it works is: There is a mechanism composed of a spring and a rubber membrane in the valve, which is connected with the valve stem. If the flow rate increases, an unbalanced force will be generated on it, causing the valve flap to move in the closing direction to reduce the flow area, reduce the flow rate, and return the flow rate to the set value. vice versa. In this way, the flow rate after the valve is always kept unchanged, and the purpose of controlling the flow rate is achieved. Installed at the thermal population and branch point of the heating system. Automatically eliminate hydraulic imbalance, improve system efficiency, and realize economic operation. The self-operated balance valve is directional, so do not install it backwards. 1.9 Safety valve When the medium pressure exceeds the specified value, the valve can automatically open and release the pressure.

When the pressure is normal, it can automatically close to ensure the normal operation of the system. The valve that plays this role is called a safety valve. According to the structure, there are: spring type, lever type and pulse type. According to the amount of action: the ratio of the opening height of the valve flap to the valve seat diameter is less than 10%, called the micro-opening type, and 20%-30% is called the full-opening type. According to the method of discharge: the medium is discharged through the pipeline called the closed type, and the direct discharge into the air is called the open type. Now take the spring type as an example to make a brief description: the spring force is balanced with the normal pressure of the medium acting on the disc to close the sealing surface; when the medium pressure is too high, the spring is compressed, the valve plate opens, and the medium leaks from it; When the pressure drops back to the normal value, the spring force closes the valve again. Safety valves are widely used in pressure vessels. 2 Common problems in valve use a) Keep the valve clean. ) When lifting, do not tie the rope to the handwheel or valve stem. c) Confirm that the valve is working properly before installation. d) When welding, the ground wire of the welder must be placed on the steel pipe of the weld on the same side to prevent current from damaging the valve. e) Cooling measures should be taken for the valves during the welding of medium and small diameter valves. f) Valves in the pipeline that are not frequently opened and closed should be rotated regularly. In addition, there are environmental corrosion and protection of the valve, medium corrosion and protection of the valve, temperature and pressure, and sealing and leakage problems. In short, although the valve is small, the knowledge is great, we need to continue to learn and summarize Discharge of the medium through the pipeline is called the closed type, and directly discharged into the air is called the open type. Now take the spring type as an example to make a brief description: the spring force is balanced with the normal pressure of the medium acting on the disc to close the sealing surface; when the medium pressure is too high, the spring is compressed, the valve plate opens, and the medium leaks from it; When the pressure drops back to the normal value, the spring force closes the valve again. Safety valves are widely used in pressure vessels. 2 Common problems in valve use a) Keep the valve clean. ) When lifting, do not tie the rope to the handwheel or valve stem. c) Confirm that the valve is working properly before installation. d) When welding, the ground wire of the welder must be placed on the steel pipe of the weld on the same side to prevent current from damaging the valve. e) Cooling measures should be taken for the valves during the welding of medium and small diameter valves. f) Valves in the pipeline that are not frequently opened and closed should be rotated regularly. In addition, there are environmental corrosion and protection of the valve, medium corrosion and protection of the valve, temperature and pressure, and sealing and leakage problems. In short, although the valve is small, the knowledge is great, we need to continue to learn and summarize Discharge of the medium through the pipeline is called the closed type, and directly discharged into the air is called the open type. Now take the spring type as an example to make a brief description: the spring force is balanced with the normal pressure of the medium acting on the disc to close the sealing surface; when the medium pressure is too high, the spring is compressed, the valve plate opens, and the medium leaks from it; When the pressure drops back to the normal value, the spring force closes the valve again. Safety valves are widely used in pressure vessels. 2 Common problems in valve use a) Keep the valve clean. ) When lifting, do not tie the rope to the handwheel or valve stem. c) Confirm that the valve is working properly before installation. d) When welding, the ground wire of the welder must be placed on the steel pipe of the weld on the same side to prevent current from damaging the valve. e) Cooling measures should be taken for the valves during the welding of medium and small diameter valves. f) Valves in the pipeline that are not frequently opened and closed should be rotated regularly. In addition, there are environmental corrosion and protection of the valve, medium corrosion and protection of the valve, temperature and pressure, and sealing and leakage problems. In short, although the valve is small, the knowledge is great, we need to continue to learn and summarize