In the pipeline system as a fluid carrier, the flow rate, pressure, and flow direction of the fluid need to be controlled. The equipment used is the valve. The valve is an important part of the pipeline system, and the gas, liquid, and gas flowing in the pipeline are used. Liquid mixtures or solid-liquid mixtures are of great significance. Under normal circumstances, the valve consists of a valve cover, a valve body, a valve seat, a drive mechanism, an opening and closing member, a seal and a fastener. It has good sealing performance, strength performance, adjustment performance, movement performance and circulation performance
Valves are required as control devices in various fluid devices. Valves, as an important part of pipeline equipment, have a role that cannot be ignored. Valves undergo stringent quality control in the manufacturing process to ensure their quality is met. The standard. However, during the use of the valve, it is unavoidable that failure will occur, resulting in leakage of the liquid, not only causing damage to the equipment, but also increasing the cost due to leakage of the liquid, affecting the realization of the economic benefits of the enterprise. This article analyzes the causes of valve leakage and proposes specific measures to prevent the occurrence of leakage.
In the pipeline system as a fluid carrier, the flow rate, pressure, and flow direction of the fluid need to be controlled. The equipment used is the valve. The valve is an important part of the pipeline system, and the gas, liquid, and gas flowing in the pipeline are used. Liquid mixtures or solid-liquid mixtures are of great significance. Under normal circumstances, the valve consists of a valve cover, a valve body, a valve seat, a drive mechanism, an opening and closing member, a seal and a fastener. It has good sealing performance, strength performance, adjustment performance, movement performance and circulation performance. In the long-term application of the valve, it is observed that where the leakage of the valve usually occurs is concentrated on the packing seal, the valve body and the flange. The damage caused by the valve leakage is very serious. When the valve leaks, it may easily cause fire, explosion and personal injury. At the same time, the life of the equipment is reduced, the production of the enterprise cannot be performed normally, and the unplanned production suspension accidents increase. Damage to the economic benefits of the enterprise, so the cause of the valve leakage should be analyzed to find out specific solutions to ensure the safety of the valve operation, and create good economic and social benefits for the company.
1. Analysis of causes of valve leakage
1.1 The valve itself has quality problems.
The part where the valve itself is prone to quality problems is divided into two parts, one part is the surface and the other part is intrinsic. Because the valve needs to control the fluid in the piping system, it has more parts in its seal, if it is There are quality problems on the exterior of the valve. Problems such as surface flaws, cracks, rust, and flange deformation are easier to detect with the naked eye, so they can also be handled in a timely manner. However, its inherent quality problems are difficult to find, which is also the main cause of valve leakage, such as internal blisters, slag, bubbles, welding defects, or improper material selection, unreasonable design, improper heat treatment, and poor connection. . The existence of these problems will cause the valve to be under the action of the fluid during use, resulting in premature valve damage or leakage.
1.2 The erosion of the internal medium causes damage to the sealing surface.
In the process of using the valve, when the internal medium flows in the pipeline, the sealing surface of the valve will produce flushing and cavitation. Under the continuous flushing and cavitation of the medium, the sealing surface of the cold door is easily damaged locally. In addition, the erosion effect of the chemical acts on the sealing surface, resulting in the valve being easily destroyed under the action of erosion, causing it to leak or even be scrapped. 1.3 Damage caused by improper selection and handling.
When selecting the valve, it is necessary to select according to the specific working conditions. Once it is selected improperly, there may be a situation of lax sealing, resulting in the occurrence of internal leakage, and at the same time distinguishing the difference and function between different valves. , thereby reducing erosion and wear on the sealing surface. In addition, if the valve is not standardized in the installation process, poor quality control measures in the installation will also cause the valve to leak. During maintenance, sand, welding slag and metal shavings should be strictly prevented from entering the valve cavity. Once these impurities enter the valve cavity, the sealing effect of the valve will have a more serious impact.
1.4 There are problems with the design and processing quality.
If the error during the valve manufacturing process is too great, the valve plate and the valve seat are not concentric, and the sealing surface does not completely match, resulting in leakage. The sealing surface is not well-processed, mainly because of defects such as cracks, air holes, and pinching on the sealing surface. This is caused by improper selection of surfacing and heat treatment or improper welding and heat treatment operations. Improper material selection or improper heat treatment can cause sealing surfaces. If the hardness is too high or too low, the sealing surface will eventually have uneven hardness and will not resist erosion. The material of the sealing surface of the valve plate and valve seat does not meet the requirements of use. The machining accuracy is not enough. The wedge angles of the valve plate and valve seat of the gate valve do not match. The width of the sealing surface is not uniform, and the degree of fit is poor, which can cause the valve plate not to reach the valve position. Not shut off and other phenomena.
2. The main measures to prevent leakage
2.1 Reasonable material selection to reduce the occurrence of corrosion.
As the carrier of the medium, the corrosiveness of the medium has a crucial influence on the leakage of the valve. The corrosiveness will be based on the chemical and physical properties of different materials. Corrosion will cause the valve to be destroyed in any case, resulting in the destruction of the valve. leakage. Therefore, during the use of the valve, anticorrosion work should be done first. Different valve materials should be chosen for the different media they carry, thereby increasing their corrosion resistance. The corrosive effect of the medium on the valve is directly related to the concentration, temperature, and pressure of the medium. As the temperature, concentration, and pressure of the medium increase, the corrosiveness will be accelerated. Because the corrosiveness produced by different media is different and has very complicated characteristics, so in the actual selection process of valve materials, it is necessary to analyze the corrosive factors generated according to different situations so as to select suitable materials.
2.2 Suitable opening and closing force to prevent damage to the sealing surface.
In the actual pipeline system, the manual valve as a normal temperature and pressure is more widely used. This type of valve is designed according to the common manpower for its hand wheel and handle, so it can only be operated by hand in the process of use, and cannot be used. Boardman to operate. Because the use of wrenches to operate, it will lead to the destruction of the stem thread, resulting in failure to start and close, causing accidents. At the same time, during operation, attention should be paid to the use of strength. Do not use excessive force to avoid damage to the handwheel or handle. In addition, when the handwheel or handle is damaged or lost, it should be immediately installed and resolutely eliminated.
2.3 properly open and close the valve to prevent damage to the valve.
For high-temperature and high-pressure valves, they should be heated beforehand, and the condensate should be removed. When opening, they should be as slow as possible to avoid water hammer. When the valve is fully open, the handwheel should be turned a little to make the threads tight so as not to loosen the damage. For the stem valve, remember to position the stem at full open and full close to avoid hitting the top dead center when fully open. If the clapper falls off or if debris is embedded between the valve plug seals, the position of the stem will be shifted when fully closed. When the valve is just activated, there is a certain amount of debris in the pipe, the valve can be opened slightly, the high-speed flow of the medium is used, the impurities are washed away, and then they are closed and opened again. This is repeated many times to flush out the impurities. For a normally open valve, there may be debris on the sealing surface, and it should be flushed repeatedly and closed after closing. If the media cools after the valve is closed, the valve plate will shrink, and the operator should close it again at an appropriate time to leave no gaps on the sealing surface.
2.4 Pay attention to the flow of valve media to prevent valve failure.
For valves such as stop valves, throttling valves, pressure reducing valves, and check valves, the medium has a certain flow direction. Such valves have permanent flow signs on the valve body. Such as throttling valves, installed inverted counter will affect the use of effects and life; Relief valve installed reversed does not play any role; For the check valve, reversed installation will cause serious danger. According to the relevant standards, the valve shall have a direction mark on the valve body; if it does not, it should be correctly identified according to the basic principle of the valve.
2.5 Correctly install the valve to extend the life of the valve.
For a high-temperature valve, since it is installed at room temperature, after normal use, the clearance will increase as the temperature increases, so it must be tightened again, otherwise leakage may occur. When the valve is put into use, the packing should not be pressed too tightly, so it is not necessary to avoid leakage, so as to avoid too much pressure on the valve stem, to accelerate the wear, and to open and close. The gate valve cannot be flipped, ie, the handwheel is down, otherwise the medium will stay in the valve cap for a long time, and it is easy to corrode the valve stem. At the same time, the operator is inconvenient to replace the filler. When the valve is installed and constructed, it must not be strongly impacted by gravity. Before installation, the valve should be inspected, check the specification model, check for damage, especially the valve stem, it is necessary to rotate a few times to see if there is a skew phenomenon, because the valve stem can easily cause damage during transportation. Iron oxide dust, mud sand, welding slag and other debris should be blown off with compressed air during installation. In order to avoid scratching the sealing surface of the valve, even a valve with a small diameter will be blocked and the valve will fail.
In summary, after analyzing the cause of valve leakage, relevant units should strengthen the implementation of valve leakage prevention measures. Strict quality control, detailed understanding of the user's media information, so that valve companies according to the valve user's media information on the design of the valve in a timely manner to ensure the quality of the valve. Before use, the quality of the valve shall be strictly inspected. It shall be strictly followed according to the rules of installation and use. The pressure shall be tested first, and the problem shall be promptly replaced. Strengthen the daily management of valves, establish a complete daily inspection system for valves, operate and maintain the valves in strict accordance with regulations, check regularly to ensure the good performance of valves, prolong the service life of valves, prevent valve leakage, and prevent Not yet.
Shanghai KS Flow Control Equipments Co.,Ltd is a valve manufacture with more than 30 years of valve manufacturing experience, which set up in 1984,specializing in Ball Valve,Gate Valve, Globe Valve, Check Valve and Butterfly Valve.
The company has advanced processing and manufacturing equipment, more than 70 CNC machine tools and machining centers, three spray lines. The company has established a complete physical and chemical laboratories, with direct reading spectrometer, spectrum alloy analyzer, helium mass spectrometer leak detector, electronic universal testing machine, coordinate measuring instrument, nondestructive testing, torque life test, high and low temperature comprehensive performance test device Etc.