Installation
1. Before installing the valve, carefully check whether the model and specifications of the valve used are consistent with the design;
2. According to the valve model and factory Check the instruction manual to see if the valve can be used under the required conditions;
3. When lifting the valve, the rope should be tied to the flange connection between the valve body and the valve cover, and not tied to the handwheel or valve stem. to avoid damaging the valve stem and handwheel;
4. When installing the valve on a horizontal pipeline, the valve stem should be vertically upward and the valve stem is not allowed to be installed downward;
5. When installing the valve, it is not allowed to use the forced connection method of pulling and pulling to avoid damage due to uneven stress;
6. The rising stem gate valve should not be installed in humid places underground to avoid corrosion of the valve stem.
Matching electric actuators
Electric actuators are mostly matched with valves and used in automated control systems. There are many types of electric actuators, each with different action modes. For example, a quarter-stroke electric actuator outputs angular torque, while a straight-stroke electric actuator outputs displacement thrust. The type of electric actuator used in the system should be selected according to the working needs of the valve. 1. Flange connection:
This is the most commonly used connection form in valves. According to the shape of the joint surface, it can be divided into the following categories:
1. Smooth type: used for valves with low pressure. Processing is more convenient
2. Concave-convex type: The working pressure is higher, and medium-hard washers can be used
3. Tongue-and-groove type: Washers with larger plastic deformation can be used, and in corrosive media It is widely used and has better sealing effect.
4. Trapezoidal groove type: Use oval metal ring as gasket, used for valves with working pressure ≥64 kg/cm2, or high temperature valves.
5. Lens type: The gasket is in the shape of a lens and is made of metal. Used for high-pressure valves or high-temperature valves with working pressure ≥100 kg/cm2.
6. O-ring type: This is a newer flange connection form. It was developed with the emergence of various rubber O-rings. It has a sealing effect in the connection form. .
2. Clamping connection:
Use bolts to directly clamp the valve and the pipes at both ends together.
3. Butt welding connection:
Directly welded to the pipe
4. Threaded connection:
This is a simple Connection method, often used for small valves. There are two situations:
1. Direct sealing: the internal and external threads directly act as a seal. In order to ensure that the joints do not leak, they are often filled with lead oil, linen and polytetrafluoroethylene raw material tapes. Among them, polytetrafluoroethylene raw material tapes are increasingly used. This material has good corrosion resistance and extremely good sealing effect. It is excellent and easy to use and store. When disassembling, it can be completely removed because it is a non-sticky film, which is much superior to lead oil and linen.
2. Indirect sealing: The force of thread tightening is transmitted to the gasket between the two planes, allowing the gasket to act as a seal.
5. Cutting sleeve connection:
The connection and sealing principle of the cutting sleeve connection is that when the nut is tightened, the cutting sleeve is under pressure, causing its blade to bite into the pipe. The outer wall and the outer conical surface of the ferrule are in close contact with the inner conical surface of the joint under pressure, thus reliably preventing leakage.
The advantages of this connection form are:
1. Small size, light weight, simple structure, easy to disassemble and assemble;
2. Strong connection force, It has a wide range of uses and can withstand high pressure (1000 kg/cm2), high temperature (650°C) and shock vibration
3. A variety of materials can be selected, suitable for corrosion prevention;
4 , The processing accuracy requirement is not high; it is convenient for high-altitude installation.
The ferrule connection form has been adopted in some small-diameter valve products in China.
6. Clamp connection:
This is a quick connection method that requires only two bolts and is suitable for low-pressure valves that are frequently disassembled.
7. Internal self-tightening connection:
The above various connection forms use external force to offset the medium pressure and achieve sealing.
In the same way, when adjusting the closing position, the corresponding adjustment of the opening position should also be considered. Ensure right angle travel of the valve.
Eighth, after grease injection, the grease injection port must be sealed. To avoid the entry of impurities or the oxidation of the lipid at the grease injection port, the cover should be coated with anti-rust grease to avoid rust. So that it can be applied in the next operation.
Ninth, when injecting grease, we should also consider the specific issues in the sequential transportation of oil products in the future and deal with them in detail. Given the different qualities of diesel and gasoline, the scour and decomposition capabilities of gasoline should be considered. In the future valve operation, when encountering gasoline section operations, replenish grease in time to prevent wear and tear.
Tenth, when injecting grease, do not ignore the grease injection of the valve stem. There is a sliding bushing or packing on the valve shaft, which also needs to be kept lubricated to reduce frictional resistance during operation. If lubrication cannot be ensured, the torque will increase during electric operation and the worn parts will be difficult to open and close during manual operation.
Eleventh, some ball valve bodies are marked with arrows. If there is no English FIOW writing, it is the direction of the sealing seat and is not used as a reference for the flow direction of the medium. The self-discharging direction of the valve is opposite. Typically, double-seat sealed ball valves have bidirectional flow.
Twelfth, when maintaining the valve, we should also pay attention to the water intrusion problem in the electric head and its transmission mechanism. Especially the rainwater that seeps in during the rainy season. One is that the transmission mechanism or transmission sleeve will rust, and the other is freezing in winter. As a result, the torque is too large when the electric valve is operated, and damage to the transmission components will cause the motor to be unloaded or the over-torque protection will trip, making it impossible to realize electric operation. The transmission parts are damaged and manual operation is impossible. After the over-torque protection action, manual operation is also unable to switch. Forcible operation will damage the internal alloy components.
The friction torque is small and the hysteresis is small. Why do rubber-lined butterfly valves and fluorine-lined diaphragm valves have short service lives when used for desalted water media? The desalted water medium contains low concentrations of acid or alkali, which are highly corrosive to rubber. Corrosion of rubber manifests as expansion, aging, and low strength. Butterfly valves and diaphragm valves lined with rubber have poor performance. The essence is that rubber is not resistant to corrosion. The rubber-lined diaphragm valve was improved to a fluorine-lined diaphragm valve with good corrosion resistance. However, the diaphragm of the fluorine-lined diaphragm valve could not withstand folding up and down and was broken, causing mechanical damage and shortening the life of the valve. The best way now is to use a special ball valve for water treatment, which can be used for 5 to 8 years. Why shut-off valves should be used as much as possible
In summary, valve maintenance must be treated with a truly scientific attitude, so that valve maintenance can achieve the desired effect and application purpose.
Frequently Asked Questions in Valve Applications
Why can't double-seal valves be used as shut-off valves? The advantage of the double-seat valve core is that it has a force-balanced structure that allows a large pressure difference. However, its outstanding disadvantage is that the two sealing surfaces cannot be in good contact at the same time, causing large leakage. If it is used artificially and compulsorily in cutting-off situations, the effect will obviously not be good. Even if many improvements are made for it (such as double sealing sleeve valve), it is not advisable. Why is the double-seat valve prone to oscillation when operating at a small opening? For a single core, when the medium is flow-open, the valve has good stability; when the medium is flow-closed, the valve has poor stability. The double-seat valve has two valve cores. The lower valve core is in flow-closed state and the upper valve core is in flow-open state. In this way, when working at a small opening, the closed-flow valve core can easily cause vibration of the valve. This is a double-seat valve. The reason why it cannot be used for small opening work. Which straight-stroke control valve has poor anti-clogging performance and which quarter-stroke valve has good anti-clogging performance? The valve core of the straight stroke valve is a vertical throttling, while the medium flows in and out horizontally. The flow path in the valve cavity must turn and reverse, making the flow path of the valve quite complicated (the shape is like an inverted S-shape). In this way, there are many dead zones, which provide space for the sedimentation of the medium, which in the long run will cause blockage. The throttling direction of the quarter-turn valve is the horizontal direction. The medium flows in horizontally and flows out horizontally, which can easily take away the dirty medium. At the same time, the flow path is simple and there is little space for the medium to settle, so the quarter-turn valve has good anti-blocking performance. Why do quarter-turn valves have a large cut-off pressure difference? The cut-off pressure difference of the quarter-turn valve is large because the resultant force generated by the medium on the valve core or valve plate exerts a very small torque on the rotating shaft. Therefore, it can withstand a large pressure difference.
Why is the stem of a straight stroke regulating valve thinner? It involves a simple mechanical principle: large sliding friction and small rolling friction. The valve stem of a straight stroke valve moves up and down. If the packing is pressed a little tighter, it will wrap the valve stem very tightly, resulting in a large hysteresis. To this end, the valve stem is designed to be very small, and the packing often uses PTFE packing with a small friction coefficient in order to reduce the hysteresis. However, the problem derived from this is that a thin valve stem is easy to bend, and the packing life is also short. To solve this problem, the best way is to use a rotary valve stem, that is, a rotary stroke regulating valve. Its valve stem is 2 to 3 times thicker than a straight stroke valve stem, and it uses graphite filler with long life and high valve stem stiffness. Good, long packing life, hard seal?
The leakage of the shut-off valve is required to be as low as possible. The leakage of the soft seal valve is the lowest. The shut-off effect is certainly good, but it is not wear-resistant and has poor reliability. From the dual standards of small leakage and reliable sealing, soft seal cutting is not as good as hard seal cutting. For example, the full-function ultra-light control valve is sealed and protected by wear-resistant alloy. It has high reliability and a leakage rate of 10 to 7, which can already meet the requirements of a shut-off valve.
Daily valve maintenance
1. The valve should be stored in a dry and ventilated room, and both ends of the passage must be blocked.
2. Valves stored for a long time should be inspected regularly, dirt should be removed, and anti-rust oil should be applied to the processing surface.
3. After installation, regular inspections should be carried out. The main inspection items are: (1) Wear of the sealing surface.
(2) Wear of the trapezoidal thread of the valve stem and valve stem nut.
(3) Whether the packing is out of date and ineffective. If it is damaged, it should be replaced in time.
(4) After the valve is repaired and assembled, a sealing performance test should be carried out.
For valves in operation, all valve parts should be complete and intact. The bolts on the flange and bracket are indispensable. The threads should be intact and no loosening is allowed. If the fastening nut on the handwheel is found to be loose, tighten it in time to avoid wearing the connection or losing the handwheel and nameplate. If the handwheel is lost, it is not allowed to use an adjustable wrench to replace it, and it should be replaced in time. The packing gland is not allowed to be skewed or have no preload gap. For valves in environments that are easily contaminated by rain, snow, dust, sand and other contaminants, a protective cover must be installed on the valve stem. The scale on the valve should be kept complete, accurate and clear. The valve seals, caps, pneumatic accessories, etc. should be complete and intact. The insulation jacket should have no dents or cracks.
It is not allowed to knock, stand on or support heavy objects on running valves; this is especially prohibited for non-metallic valves and cast iron valves.
After decades of development, my country's valve manufacturing industry has made great progress, and valve output has increased significantly.
my country's valve manufacturing industry will surely show better development prospects under the huge demand environment. As the world economy that has experienced the financial crisis is gradually recovering, China's import and export market for valve mechanical and electrical products is also gradually growing steadily, and the international competition in the valve industry will become more intense. Comparing our country's valve manufacturers with large foreign valve manufacturers, we have a big gap mainly in high-end technology. Product technology innovation and improvement have become a major stumbling block to the rapid development of Chinese valve products.
Valve is an important fluid control equipment in industry, involving many sectors of the national economy, and is an important basic equipment for the development of the national economy. After decades of development, my country's valve products have formed more than a dozen categories, ranking among the top in the world in terms of number of companies and production and sales. However, most of them are small-scale, low-level valve companies, and their products are also mid- to low-end. host.
Since the reform and opening up, the valve market has expanded rapidly. State-owned enterprises have encountered the crisis of closure and transfer due to the influence of the system. Township and private enterprises can only carry out imitation production due to limited technical strength. This has caused the quality of domestic valves to deteriorate. The main reason for the lower. The country has introduced policies to revitalize the equipment manufacturing industry, with particular emphasis on supporting the development of general basic manufacturing industries. Our country is facing the transition from the agricultural era to the industrialization era, which will significantly increase the industrial demand for valve products. The support of national policies and the huge demand of the product market will be a powerful driving force for the rapid development of the valve industry.
Market analysts believe that the development trend of valves will be the main topic in the market for quite some time. Future models will tend to develop and apply in the following aspects.
First of all, develop hydraulic control valves with excellent performance, such as hydraulic control valves with large discharge capacity, high sensitivity, corrosion resistance, friction resistance, and zero leakage, and develop integrated technology, electronic computer technology, and monitoring technology. High-end hydraulic control valves, develop products with good operational feasibility, high safety and good comfort.
Secondly, develop high-performance large-scale regulating valves to meet the needs of major engineering projects in our country, develop micro-regulating valves to meet the needs of narrow and small operations such as trenching and burying cables, and develop to adapt to power stations. , petroleum, coal, water conservancy, farmland, and urban construction; develop intelligent electric control valves that can monitor, control and improve the working conditions of operators in various working conditions of the control valve. Promising products are: large and medium-sized intelligent electric control valves, micro-intelligent electric control valves, and remote-controlled intelligent electric control valves.
In addition, develop high-level products with high safety, high feasibility and good performance, develop integrated large valves equipped with advanced electronic technology, and develop deformed products towards generalization, standardization and serialization direction development.
Experts pointed out that in agricultural production, the application of various agricultural shed films, mulch films, agricultural water-saving valve equipment and other valve pipelines are widely used in modern agriculture, and the application of valve pipelines in rural areas is also increasing. It is only a solution to The demand for valves and pipes used in water supply projects for humans and animals is considerable. The demand for various valves and pipelines in urban buildings has also increased significantly. The automobile manufacturing industry is increasingly using valves to manufacture automobile parts. The average number of valves used in power stations in developed countries has exceeded 10 billion, and the average number of valves used in power stations in my country is 7 billion. These have stimulated market demand in the valve industry.
China's valve manufacturing industry has been able to provide user departments with about twelve categories, more than 3,000 models, and more than 4,000 specifications of products, with performance parameters ranging from vacuum valves to 1,000Mpa ultra-high pressure valves, temperature From a deep freeze of -196 degrees Celsius to a high temperature of 570 degrees Celsius. The main products of China's valves can basically meet the needs of the domestic market. The complete set rate, complete set level and complete set capacity of the valve market have been greatly improved. Domestic valves already have a certain foundation for revitalization.
However, my country's valve industry is still dominated by small and medium-sized enterprises. China's valve manufacturing industry will definitely show better development prospects under the huge demand environment.
From January to November 2007, China's valve and cock manufacturing industry achieved a cumulative total industrial output value of 84,288,398 yuan, an increase of 31.47% over the same period last year; a cumulative product sales revenue of 80,571 yuan , 055,000 yuan, an increase of 29.36 over the same period last year; the total cumulative profit was 5,772,097 thousand yuan, an increase of 44.16 over the same period last year. From January to August 2008, China's valve and cock manufacturing industry achieved a cumulative total industrial output value of 73,321,603,000 yuan, an increase of 27.02 over the same period last year; a cumulative product sales revenue of 70,451,147,000 yuan, An increase of 27.27% over the same period last year; the total cumulative profit achieved was 4,470,009,000 yuan, an increase of 15.37% over the same period last year. During the "Eleventh Five-Year Plan" and the next few years, China's petrochemical, natural gas, metallurgical industries, electric power, urban construction and other industries will have a large demand for valves. During the "Eleventh Five-Year Plan" period, China's total demand for valves will reach 345 billion, therefore, the valve industry has huge market development space. my country's valve production technology has made certain achievements. However, due to the limitations of the casting process level, my country's valve industry wastes a lot of raw materials such as cast steel and cast iron during the production process. Facing the increasingly fierce competition in the valve market and the increasingly tight resource market, a large amount of waste in the casting process is not conducive to cost savings in our country's valve industry, and is not conducive to our country's valve industry striving for greater success in the fierce market competition. living space, which is not conducive to the long-term development of the valve industry.
In order to save production costs, free up more production space for the valve industry, and for the long-term and healthy development of the valve industry, my country's valve industry must avoid material waste in the casting process. On the one hand, this can be achieved by improving the conservation awareness of foundry workers; on the other hand, enterprises need to increase scientific research efforts, develop new casting processes or introduce new casting equipment to better avoid waste caused in the casting process. , to save production costs and improve valve quality
Valve specifications and categories should comply with the requirements of pipeline design documents. 1. The valve model should indicate the national standard number requirements based on it. If it is an enterprise standard, the relevant description of the model should be indicated. 2. The working pressure of the valve must be ≥ the working pressure of the pipeline. Without affecting the price, the working pressure that the valve can withstand should be greater than the actual working pressure of the pipeline. 3. The valve manufacturing standard should indicate the national standard number it is based on. If it is an enterprise standard, the enterprise document should be attached to the procurement contract.
Valve performance testing: 1. When a valve of a certain specification is manufactured in batches, an authoritative organization should be entrusted to conduct the following performance testing: ① The opening and closing torque of the valve under working pressure conditions; ② The valve in the pipeline Detection of flow resistance coefficient under water conditions. 2. The valve should undergo the following tests before leaving the factory: ① When the valve is open, the valve body should withstand an internal pressure test that is twice the valve working pressure; ② When the valve is closed, both sides of the valve should withstand 11 times the valve working pressure. value, no leakage; but for metal-sealed butterfly valves, the leakage value is not greater than the relevant requirements.