Discussion on common valves in the hottest heat su

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Discussion on common valves in heat supply engineering

there are many kinds of valves used in heat supply system. Such as gate valve, globe valve, ball valve, butterfly valve, check valve, safety valve, regulating valve, balance valve, self operated balance valve, etc. Next, we will introduce them one by one

1.1 gate valve

gate valve is also a widely used valve

working principle: the sealing surface of the ram 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 ram conducts and shuts off the medium through the lifting and pressing of the valve rod. It plays a shut-off role in the pipeline

advantages: low fluid resistance; When fully opened, the sealing surface will not be eroded; It can be used when the medium flows in both directions, without directionality; Strong and durable; It is not only suitable for making small valves, but also for making large valves

disadvantages: high height; Long opening and closing time; Bulky; Difficult to repair; If it is a large-diameter gate valve, manual operation is laborious

gate valves are divided into rod type and Non rising rod type according to different valve stems; It can be divided into parallel type and wedge type according to different ram structures; There are also single ram and double ram. In heating engineering, rising stem wedge single gate valve (z41h-16c) and Non rising stem wedge single gate valve (z45t-10) are commonly used. 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 a main device, it acts as a switch; As auxiliary equipment, it is installed in front of and behind the main equipment for maintenance


, do not keep the handwheel below the horizontal line (flip), otherwise the medium will remain in the bonnet for a long time, which is easy to corrode the valve stem

in heating engineering, gate valves used to be the main force in valves. Now with the wide use of butterfly valves, gate valves have been replaced by butterfly valves

1.2 stop valve

is also a widely used valve. Generally, the caliber is less than 100 mm. Its working principle is similar to that of the gate valve, except that the closing part (disc) moves along the center line of the valve seat. It plays a shut-off role in the pipeline and can also roughly adjust the flow

advantages: easy to manufacture, convenient to maintain, strong and durable

disadvantages: only one-way flow of media is allowed, and there is directionality during installation. Large flow resistance and poor sealing

it can be divided into straight through type, right angle type, direct current type and balanced type according to different structures. Flange straight through type (J41H) and internal thread straight through type (j11h) are generally used in projects. The stop valve is directional and cannot be pressed reversely. It's not appropriate to go down

in our production and life, straight through and small-diameter stop valves used to be used in the past have been gradually replaced by ball valves

1.3 ball valve

compared with gate valve and, ball valve is a new type of valve that is gradually widely used. Its working principle is: it is a sphere with a cavity, and the valve core is controlled to rotate 90 ° through the valve rod to make the valve unblocked or blocked. It plays a shut-off role in the pipeline

advantages: in addition to the advantages of gate valve and stop valve, it also has the advantages of small volume, good sealing (zero leakage) and easy operation. At present, it is widely used in petrochemical, electric power, nuclear power, aviation, aerospace and other ministries

disadvantages: it is difficult to maintain

there are two types of ball valves: floating ball type and fixed ball type. In heat supply projects, some key positions, such as the development of important branches and heat stations, rare earth doped optical fibers, research and development of processing technology of high-density ceramic materials for optical fiber connectors, and people below DN250, often use imported ball valves. Its structure is different from that of domestic ball valves: the valve body of domestic ball valves is generally two-piece or three piece, with flange connection; The valve body of the imported ball valve is one-piece, welded and connected, with fewer failure points. Its origin is in northern Europe, such as Finland, Denmark and other countries with relatively developed heating technology. Such as naval and vexve in Finland, dafoss in Denmark, etc. Because of its excellent sealing and reliability of operation, 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 avoid electric sparks from damaging the surface of the ball during welding; When installing in the vertical pipeline, if the joint is welded, the valve must be opened. If the lower joint is welded, the valve must be closed to avoid high heat burns inside the valve

1.4 butterfly valve

in the heating system, it is currently the most widely used valve with the most types. Working principle: it is a disc. Through the rotation of the valve stem, the valve disc rotates at 90 ℃ within the valve seat range to realize the opening and closing of the valve. It plays a shut-off role in the pipeline

flow can also be adjusted

advantages: simple structure, light volume, convenient operation and good sealing

disadvantages: when fully opened, the valve plate (sealing ring) is eroded by the medium

in heat supply projects, butterfly valves used include three eccentric metal seal butterfly valves and rubber soft seal butterfly valves

1.4.1 tri eccentric metal seal butterfly valve

the so-called "tri eccentric" refers to the deviation of the relative position of the valve shaft and valve plate in the valve *. Ordinary butterfly valves are eccentric, that is, the centerline of the valve shaft deviates from the centerline of the sealing surface (the centerline of the valve plate); High performance plus an eccentricity, that is, the centerline of the valve shaft deviates from the centerline of the valve (pipeline centerline); The purpose of double eccentricity is to separate the sealing pairs after the valve plate is opened to 20 °, so as to reduce friction (cam effect). The triple eccentric butterfly valve adds a unique eccentric inclined cone on the basis of the double eccentric, that is, the offset of the valve plate (the sealing surface is inclined at an angle with the vertical surface of the pipe). In this way, the valve * is completely separated from the sealing pairs within the 90 ° stroke range, which not only strengthens the cam effect, but also completely eliminates friction; When the valve * is closed at the same time, when the sealing pair is gradually closed, a "wedge effect" is generated, and the tightest shutoff is achieved with the minimum torque

the so-called "metal seal" refers to 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 hard contact 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", so as to ensure that it is tightly closed and opened without friction. With the "three eccentric" structure, supplemented by "elastic metal seal", such a valve is easy to operate, durable and well sealed

three eccentric metal seal butterfly valves are generally used in the main lines and branches of heating systems *. The diameter is DN300 with *

the imported three eccentric metal seal butterfly valve has no directionality, but generally, only in this way can the accuracy of the experimental results. It is suggested that the installation direction should not be reversed; Domestic ones are directional. Generally, the reverse direction is one leakage level worse than the forward direction or one to two pressure levels worse. Reverse installation is not allowed. If welding in horizontal pipeline, close the valve to protect the sealing ring; If welding in vertical pipes, the valve should be closed, and water should be injected into the valve plate * during welding to extinguish the welding slag. When installing horizontal pipes, it is recommended that the valve stem be horizontal or inclined to the vertical direction to ensure that the cleaning rod at the bottom bearing is clean

1.4.2 rubber soft seal butterfly valve

the butterfly plate is generally galvanized ductile iron, and the sealing ring is made of rubber material. Different sealing materials have different properties. Commonly used are: butadiene rubber, applicable temperature - 12 ℃ - 82 ℃; Ethylene propylene rubber, applicable temperature - 45 ℃ - 135 ℃; Heat resistant ethylene propylene rubber, applicable temperature - 20 ℃ - 150 ℃

commonly used in heat supply projects are wafer type (d371x) and flange type (D341X). Handle drive (D71, D41X) can be used below DN125. The wafer type butterfly valve is small and light, quick to open and close, easy to operate, easy to install, easy to maintain, with good sealing and adjustment performance and high cost performance, so it should be vigorously used. The soft seal butterfly valve has no directionality and can be installed at will

when the butterfly valve is stored, the valve plate should be opened 4 ° - 5 °. In order to prevent the sealing ring from deforming due to long-term pressure and affecting the sealing

1.5 check valve

is also called check valve and single flow valve. A commonly used auxiliary valve. Working principle: a valve that automatically opens and closes depending on the force of the fluid itself and the self weight of the valve disc. As the name suggests, its function is to prevent media backflow. It is generally installed at the outlet of the water pump to prevent water hammer from damaging the water pump. Commonly used in heating engineering are horizontal lifting type (h41h), single valve swing type (h44h), double valve butterfly type (h77h). The check valve is directional and must not be installed reversely. 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 in the horizontal pipeline, and ensure that the valve disc is in a vertical state; The single flap swing type can only be installed in the horizontal pipeline, and ensure that the disc rotating shaft is in a horizontal state; Double valve butterfly type can be installed at will. 1. Set the friction times 5. Turn the speed regulating knob 6. The regulating valve is also called throttle valve. It is a common valve for secondary heating system. Working principle: the shape and structure are similar to the stop valve. Only the sealing pair is different. The valve disc and valve seat of the regulating valve are similar to the cork and mouth of a warm water bottle. The flow can be adjusted by changing the flow area through the movement of the valve disc. 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. Straight through type (t41h) was once used in heating engineering, but it has some disadvantages: large flow resistance, not suitable for vertical installation. Therefore, with the progress of technology, the balance valve (ph45f) replaced the regulating valve. 1.7 balance valve improved regulating valve. The flow passage adopts direct flow type, and the valve seat is changed to polytetrafluoroethylene; It has two advantages: more reasonable sealing and cut-off function. It is used for the second time in the heating station in the heating engineering, and has excellent flow regulation characteristics, especially suitable for variable flow systems. Directional, can be installed horizontally or vertically. 1.8 self operated balance valve is also called flow control valve. Its working principle is: there is a mechanism composed of spring and rubber film in the valve, which is connected with the valve rod. If the flow increases, an unbalanced force will be generated in it, making the valve disc move towards the closing direction, so as to reduce the overflow area, reduce the flow, and return the flow to the set value. vice versa. Thus, the flow behind the valve is always kept unchanged to achieve the purpose of controlling the flow. Thermal population and branch points installed in the heating system. Automatically eliminate hydraulic imbalance, improve system efficiency and realize economic operation. The self operated balance valve has directionality, so do not install it reversely. 1.9 safety valve when the medium pressure exceeds the specified value, the valve can automatically open and relieve the pressure. When the pressure is normal, it can automatically close to ensure the normal operation of the system. The valve playing this role is called safety valve

there are spring type, lever type and pulse type according to the structure

according to the amount of action: the ratio of disc opening height to valve seat diameter is less than 10%, which is called micro open type, and 20% - 30% is called full open type

according to the discharge mode: the medium is called closed type when it is discharged through the pipeline, and open type when it is directly discharged into the air

now take the spring type as an example: the spring force is balanced with the normal pressure of the medium acting on the valve disc to close the sealing surface; When the medium pressure is too high, the spring is compressed, the valve plate is opened, and the medium is discharged from it; When the pressure drops back to the normal value, the spring force closes the valve again. It is widely used in pressure vessels

2 common problems in the use of valves

a) keep the inside clean. b) When lifting, do not tie the rope to the handwheel or valve stem. c) Make sure the valve works normally before installation. d) During welding, the ground wire of the welding machine must be laid on the steel pipe at the welded junction on the same side to prevent current from damaging the valve. e) Cooling measures should be taken during the welding of medium and small diameter valves. f) The valve in the pipeline that is not often opened and closed should be rotated regularly. In addition, there are environmental and protection problems, medium corrosion and protection problems inside the valve, temperature and pressure problems, sealing and leakage problems, etc. In short, although the valve is small, the knowledge is great, and we need to continue to learn

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