1. 1 gate valve, also known as gate valve and 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 tight sealing pair. The gate opens and closes the medium through the upward and downward pressure of the valve stem. It plays a closing role in the pipeline. Advantages: small fluid resistance; When fully opened, the sealing surface is not corroded; It can be used under the condition that the medium flows in two directions, without directionality; Strong and durable; It is not only suitable for manufacturing small valves, but also suitable for manufacturing large valves. Disadvantages: high height; Long opening and closing time; Heavy; Difficult to repair; If it is a large-caliber gate valve, manual operation is laborious. Gate valves are divided into rod type and concealed rod type according to different valve stems; According to the gate structure, it can be divided into parallel type and wedge type; There are also single ram and double ram. In heating engineering, there are common wedge-type single gate valves with exposed stem (Z4 1H- 16C) and hidden stem (Z45T- 10). The former is installed on the primary side of the thermal power station, and the latter is installed on the secondary side of the thermal power station. It generally plays two roles: as the main device, it plays the role of switch; As an auxiliary equipment, it is installed before and after the main equipment for maintenance. When installing the gate valve, do not make the handwheel lower than the horizontal line (upside down), otherwise the medium will stay in the valve cover for a long time, which will easily corrode the valve stem. Gate valve used to be the main force of heating project. Now with the wide use of butterfly valves, gate valves have been replaced by butterfly valves. 1.2 globe valve is also a widely used valve. Generally, the diameter is below 100 mm, and its working principle is similar to that of gate valve, except that the closing plate (disc) moves along the center line of the valve seat. It plays the role of shut-off in the pipeline, and can also roughly adjust the flow. Advantages: easy to manufacture, convenient to maintain and durable. Disadvantages: Only one-way flow of medium is allowed, and the installation is directional. Large flow resistance and poor sealing performance. According to different structures, it can be divided into straight type, right angle type, direct current type and balance type. Flange straight-through type (J4 1H) and internal thread straight-through type (J 1 1H) are generally adopted in engineering. The stop valve is directional and cannot be pressed backwards. It is not appropriate to step back. In our production and life, the straight-through and small-caliber globe valves used in the past have been gradually replaced by ball valves. 1.3 ball valve Compared with gate valve and globe valve, ball valve is a new type of valve that is gradually widely used. Its working principle is that the valve core is a sphere with a through cavity, and the valve core is rotated by 90 degrees through the valve stem to make the valve unblocked or blocked. It plays a closing role in the pipeline. Advantages: In addition to the advantages of gate valve and globe valve, it also has the advantages of small volume, good sealing (zero leakage) and convenient operation. At present, it is widely used in petrochemical, electric power, nuclear energy, aviation, aerospace and other departments. Disadvantages: maintenance is difficult. There are two types of ball valves: floating ball type and fixed ball type. In heating engineering, imported ball valves are often used in some key positions, such as important branch pipes and thermal power stations with population below DN250. Different from the structure of domestic ball valves: the valve body of domestic ball valves is generally two-piece or three-piece with flange connection; Imported ball valve body is integrated, welded and connected, with few fault points. Its origin is northern Europe, such as Finland, Denmark and other countries with relatively developed heating technology. Such as naval in Finland, vexve in Denmark, DAFOSS, etc. Because of its good sealing and reliable operation, it has long been favored by users. 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 avoid electric spark damage to the ball surface during welding; When installed on a vertical pipe, the valve must be opened if the upper interface is welded, and closed if the lower interface is welded, so as to avoid the internal part of the valve being burned by high heat. 1.4 butterfly valve is the most widely used and varied valve in heating system at present. How it works: A disk is a disk. Through the rotation of the valve stem, the disc rotates 90℃ within the valve seat range to realize the opening and closing of the valve. It plays a closing role in the pipeline. The flow can also be adjusted. Advantages: simple structure, light volume, convenient operation and good sealing performance. Disadvantages: When fully opened, the valve plate (sealing ring) is corroded by medium. In the heating project, the butterfly valves used are 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 eccentricity" refers to the deviation of the relative position of the valve shaft and the valve plate in the valve. Ordinary butterfly valve is eccentric, that is, the center line of the valve shaft deviates from the center line of the sealing surface (the center line of the valve plate); High performance plus eccentricity, that is, the center line of the valve shaft deviates from the center line of the valve (pipeline center line); The purpose of double eccentricity is to make the sealing pairs separate from each other after the valve plate is opened to 20, thus reducing friction (cam effect). The triple eccentric butterfly valve adds a unique eccentric-inclined cone on the basis of the above double eccentricity, that is, the valve plate deviation (the sealing surface inclines at a certain angle with the vertical plane of the pipeline). In this way, the sealing pair of the valve is completely separated within the 90 stroke range, which not only strengthens the cam function, but also completely eliminates the friction; When the valves are closed at the same time, when the sealing pair is gradually closed, the "wedge effect" is generated, and the tightest shut-off is realized with the minimum torque. The so-called "metal seal" means that the valve seat and sealing ring are made of high-quality alloy with wear resistance, corrosion resistance and high temperature resistance; At the same time, in order to avoid the collision between the sealing ring and the valve seat, the sealing pair is designed to be in flexible contact, that is, to form an "elastic metal seal" to ensure that it can be closed and opened tightly without friction. Adopting "three eccentric" structure, supplemented by "elastic metal seal", this valve is convenient to operate, durable and good in sealing. Tri-eccentric metal sealing butterfly valve is generally used for the main pipeline and main pipeline of heating system. The caliber is above DN300. Imported triple eccentric metal sealing butterfly valve has no directionality, but generally it has suggested installation direction, which is not suitable for reverse installation; Domestic products are directional. Generally, the reverse direction is one leakage level or one or two pressure levels worse than the forward direction, and it cannot be reversed. If welding is carried out on a horizontal pipeline, the valve should be closed to protect the sealing ring; If welding on vertical pipes, the valve should be closed, and water should be injected into the valve plate when welding the upper opening to extinguish the welding slag. When installed on a horizontal pipeline, it is recommended that the valve stem tilt horizontally or vertically to ensure the cleanliness of the bottom bearing. 1.4.2 The butterfly plate of rubber soft sealing butterfly valve is generally made of electroplated ductile iron, and the sealing ring is made of rubber. Different sealing materials have different characteristics. Commonly used are: nitrile rubber, the applicable temperature is12℃+82℃; Ethylene propylene rubber, the applicable temperature is 45℃+135℃; Heat-resistant ethylene-propylene rubber, applicable temperature -20℃-+ 150℃. There are clip-on type (D37 1X) and flange type (D34 1X) commonly used in heating engineering. Under DN 125, it can be driven by the handle (D7 1, D4 1X). Wafer butterfly valve has the advantages of small size, light weight, quick opening and closing, convenient operation, easy installation and maintenance, good sealing and adjustment performance, high cost performance, etc., and should be vigorously adopted. Soft sealing butterfly valve has no directionality and can be installed at will. When storing butterfly valves, the valve plate should be opened 4-5 degrees. In order to avoid the deformation of the sealing ring under long-term pressure and affect the sealing. 1.5 check valve is also called check valve and check valve. Commonly used auxiliary valve. Working principle: a valve that automatically opens and closes depending on the power of the fluid itself and the weight of the disc. As the name implies, its function is to prevent the medium from flowing backwards. Generally installed at the outlet of the pump to prevent water hammer from damaging the pump. Horizontal lifting type (H4 1H), single flap swinging type (H44H) and double flap butterfly type (H77H) are commonly used in heating engineering. Check valves are directional and cannot be installed in reverse. Different types of check valves have fixed installation methods according to their structures, and must not be installed incorrectly. The horizontal lifting type can only be installed on the horizontal pipeline, and ensure that the disc is in a vertical state; Single-swing crane can only be installed on horizontal pipeline, and ensure that the rotating shaft of the disk is in a horizontal state; Double butterflies can be installed at will. 1.6 control valve is also called throttle valve. It is a common valve in the secondary pipe network of heating system. Working principle: the shape and structure are similar to the stop valve. Only the sealing pair is different. The disc and valve seat of the regulating valve are similar to the cork and bottle mouth of a thermos bottle, and the flow rate is adjusted by changing the flow area through the movement of the disc. There is a scale on the valve stem to indicate the corresponding flow. Function: Adjust the medium flow distribution between pipelines to achieve thermal balance. T4 1H has been used in heating engineering, but it has some disadvantages: large flow resistance, and it is not suitable for vertical installation. So with the development of technology, the balance valve (PH45F) replaced the regulating valve. 1.7 improvement of control valve of balance valve. The flow passage adopts direct flow type, and the valve seat is changed to PTFE; It overcomes the shortcoming of large flow resistance and adds two advantages: more reasonable sealing and cut-off function. The secondary network of heating station used in heating engineering has excellent flow regulation characteristics, especially suitable for variable flow system. Orientation, can be installed horizontally or vertically. 1.8 self-operated balance valve is also called flow control valve. Its working principle is that there is a mechanism composed of spring and 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, which will make the disc move in the closing direction, thus reducing the flow area, reducing the flow rate and returning the flow rate to the set value. Or conversely, Dallas goes to the auditorium. Therefore, the flow behind the valve is always constant to achieve the purpose of controlling the flow. The hot population is installed at the branch point of the heating system. Automatically eliminate hydraulic imbalance, improve system efficiency and realize economic operation. Self-balancing valve is directional, so don't install it backwards. 1.9 safety valve When the medium pressure exceeds the specified value, the valve can automatically open and release the pressure, and 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 disc opening height to seat diameter is below 10%, which is called slightly open type, and 20%-30% is called fully open type. According to the discharge mode: the medium discharged through the pipeline is called closed, and the medium discharged directly into the air is called open. Now take the spring type as an example to make a brief introduction: the spring force and the normal pressure of the medium acting on the disc are balanced to close the sealing surface; When the medium pressure is too high, the spring is compressed, the valve plate opens and the medium leaks out. When the pressure returns to normal, the spring force closes the valve again. Safety valves are widely used in pressure vessels.
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