Analysis of the Causes of Gate Valve Vibration and Preventive Measures

Thread Content

Analysis of the Causes of Valve Vibration and Preventive Measures Analysis of the Causes of Valve Vibration and Preventive Measures I. Structural Characteristics of Gate Valves and Their Relationship with Vibration 1.1 Structural Features of Cantilever Beams The gate plate of a gate valve functions like a cantilever beam, with one end connected to the valve stem and the other end being in a free state. When the valve is partially open, the bottom of the gate hangs in the air, supported only by its connection to the valve stem at the top. This structure results in extremely poor rigidity of the gate plate, making it highly prone to vibration under fluid impact. When fluid passes through a partially open gate valve, Karman vortices are generated downstream of the gate plate; these alternately shedding vortices exert a periodic and alternating lift force on the gate plate. Under the action of alternating forces, the cantilever-type gate plate sways back and forth, just like a stick stuck in soft soil that is pushed rhythmically. When the frequency at which vortices detach is close to or matches the natural frequency of the gate, resonance occurs, resulting in severe vibrations and noise, which pose a serious threat to the stable operation of the gate valve. 1.2 Function and influence of the clearance: To ensure that the gate can move up and down smoothly within the valve body, a clearance must exist between the gate and the guide rails of the valve body. This gap becomes an important factor causing vibration during the operation of the gate valve. When fluid flows through a partially opened gate valve, the hydrodynamic forces generated act on the gate plate. Due to the presence of the gap, the gate plate cannot be fully secured, and under the impact of fluid dynamics, it undergoes slight oscillations within the range of that gap. Such oscillation not only affects the sealing performance of the gate valve, but also causes friction and collision between the gate and the guide rails of the valve body, further intensifying the vibration. Furthermore, as the vibration continues, the gap may gradually increase, resulting in a larger swing amplitude of the gate plate and an increasingly severe vibration problem, which damages the structural strength and stability of the gate valve. II. Vibration Caused by Fluid Dynamics Reasons 2.1 Generation and Effects of Karman Vortex Strips In gate valves, when fluid flows at a certain speed through a partially open valve, the obstruction posed by the gate plate to the flow of fluid causes alternating rows of vortices with opposite rotation directions to form periodically on both sides downstream of the gate plate. After undergoing nonlinear effects, these vortices give rise to Karman vortex strips. These vortex streets generate periodic, alternating lift forces on the gate plate, causing it to oscillate slightly. Resonance occurs when the frequency at which vortices detach is close to or matches the natural frequency of the gate itself, resulting in severe vibration and noise in the gate valve. The frequency of the Karman vortex street is related to factors such as fluid velocity and gate size, and its impact on gate vibration also changes with these factors; it is one of the major causes of valve vibration. 2.2 Cavitation phenomenon and its hazards: Cavitation in gate valves occurs mainly when the fluid passes through the throttling section of the gate valve, causing the flow velocity to increase sharply and thus leading to a sudden drop in static pressure. When the pressure drops below the saturated vapor pressure of the medium, the liquid vaporizes to form small bubbles. When these bubbles flow with the fluid to the downstream high-pressure region, they collapse instantaneously, generating extremely intense local shock waves. Cavitation poses a severe threat to the vibration and lifespan of gate valves. In terms of vibration, the continuous collapse of bubbles generates intense vibrations, causing the gate valve and the entire pipeline system to shake ； In terms of lifespan, the continuous collapse of thousands of bubbles can cause severe damage to the surface of the gate or valve seat, significantly reducing the service life of the internal components of the valve. It may also lead to problems such as noise pollution, posing a serious threat to the proper operation of the gate valve. 2.3 Analysis of flashing phenomenon The flashing phenomenon in gate valves usually occurs when, after the fluid passes through the gate valve and is throttled, the pressure remains below the saturated vapor pressure. At this point, the liquid will continue to boil and vaporize, forming a gas-liquid two-phase flow. The flow of this two-phase flow is extremely unstable, and it exerts forces on the gate valve, causing vibrations. On the one hand, the gas-liquid two-phase flow generated by flashing complicates the flow pattern within the channel; the direction and magnitude of the force exerted by the fluid on the gate plate keep changing, resulting in vibration of the gate plate ； On the other hand, the bubbles generated during the flashing process release energy when they collapse, which exacerbates the vibration of the gate valve and has an adverse effect on its structural strength and stability. III. Vibration Caused by Installation and System Issues 3.1 Impact of Improper Operating Positions When a gate valve operates at a low opening degree (such as 10%-30%), its hydrodynamic properties change significantly, which in turn leads to increased vibration. At this stage, throttling is most severe; the flow channel suddenly narrows, the flow velocity increases sharply, and the impact force of the fluid on the gate plate becomes significantly greater. Strong vortices and turbulent regions tend to form downstream of the gate, leading to more intense formation of Karman vortex streets, which in turn has a more pronounced effect on the alternating lift force acting on the gate. At small opening angles, the gate slab has the longest cantilever length and the lowest structural stiffness, making it more prone to slight oscillations under strong hydrodynamic forces. When these oscillation frequencies approach the natural frequency of the gate, resonance is very likely to occur, causing the amplitude of vibration to increase sharply. This poses a serious threat to the stable operation of the gate valve and its structural integrity, and it can also lead to problems such as noise pollution and seal failure. 3.2 Pipe support issue: Improper pipe support can have a significant impact on the vibration of gate valves. If the pipes upstream and downstream of the valve are not properly supported, the pipes themselves may vibrate due to factors such as fluid flow and external loads. These vibrations are transmitted directly to the gate valve, subjecting it to additional excitation forces that exacerbate its vibration. Furthermore, pipeline vibration may also induce resonance between the gate valve and its connected components. When the vibration frequency of the pipeline is close to or matches the natural frequency of certain components of the gate valve, resonance occurs, resulting in a significant increase in the vibration amplitude of the gate valve. In severe cases, this can lead to mechanical damage such as broken valve stems, damaged gate plates, or seat sealing surfaces, and it may even cause more widespread vibrations within the pipeline system, posing a serious threat to the safe operation of the entire pipeline system. 3.3 Effects of high fluid flow velocity: Excessively high system flow velocity can significantly increase the vibration of the gate valve. When the fluid flows through the gate valve at too high a speed, the impact force of the fluid on the gate plate increases significantly. High-speed fluid generates intense turbulence and vortices inside the gate valve, resulting in greater fluid excitation forces that make it easier for the gate to swing. Furthermore, at high flow rates, the frequency and intensity of the Karman vortex street increase, resulting in a more pronounced alternating lift force on the gate plate, which makes resonance more likely to occur. At the same time, excessively high flow rates can also lead to increased cavitation and flashing; the continuous collapse of bubbles and the impact of two-phase flow further exacerbate the vibration of the gate valve. Prolonged severe vibration not only damages the internal components of the gate valve but can also lead to fatigue failure, causing cracks in the valve body or related pipelines, which affects the proper operation of the gate valve as well as the safe and stable functioning of the pipeline system. IV. Vibration Caused by Other Mechanical Reasons 4.1 Valve Stem Vibration The valve stem of a gate valve is usually long and slender and subjected to large loads, making it prone to vibration under the influence of fluids. When a fluid flows through a gate valve at a certain velocity, a complex flow field forms around the valve stem, resulting in unstable hydrodynamic forces. These hydrodynamic forces exert lateral and longitudinal impulsive forces on the valve stem, causing it to undergo bending and torsional vibrations. The vibration of the valve stem directly causes the gate connected to it to vibrate as well, increasing the amplitude of the gate’s swinging. Furthermore, valve stem vibration can also lead to increased friction between the valve stem and the packing, resulting in wear of the packing and affecting the sealing performance. Severe stem vibration can even lead to the breakage of the stem, posing a significant threat to the proper operation of the gate valve. 4.2 Effect of loose components: During long-term operation, due to factors such as vibration and corrosion, the internal connection threads or mating components of the gate valve may become loose. Loose parts can compromise the overall structural stability of the gate valve, altering the fit and relationship between its components. When fluid flows through a gate valve, the loose components undergo additional shaking and impact under the action of hydrodynamic forces, creating an additional source of vibration. These vibration sources not only exacerbate the vibration of the gate valve itself, but may also cause other components to loosen, creating a vicious cycle. The impact of loose components can also damage the internal structure of the gate valve, such as the seat sealing surface, thereby affecting the valve’s sealing performance and service life. V. Hazards of gate valve vibration 5.1 Mechanical damage situations Gate valve vibration can lead to numerous mechanical damage issues. Valve stem fracture is one of the common issues; continuous vibration subjects the slender valve stem to alternating stresses, and once these exceed its strength limit, fracture occurs. The sealing surfaces of the gate or valve seat can also be damaged due to vibration. The impact of fluid and vibrations cause the gate to repeatedly strike against the valve seat, resulting in damage such as scratches and dents on the sealing surfaces. Thread wear during connection is also inevitable; vibrations subject the threaded connections to continuous impact and friction, leading to loosening, wear, and even failure of the threads. Such mechanical damage can not only affect the normal opening, closing, and sealing functions of gate valves, but may also lead to more serious equipment failures and safety accidents. 5.2 Fatigue failure issue: Continuous vibration stress has a significant impact on the metal fatigue of gate valves. Under the repeated action of alternating vibrational stress, the properties of the metal material in a gate valve gradually change. Even if the stress level is below the material’s tensile strength or yield limit, sudden fracture of the metal component can still occur after a certain number of cycles. This fatigue fracture usually begins at the stress concentration areas of the gate valve, such as the corners of the valve body and welds, where cracks gradually form and spread, eventually causing the gate valve to lose its load-bearing capacity. Fatigue failure not only shortens the service life of gate valves, but may also cause serious accidents such as leaks and explosions in pipeline systems, posing a threat to production safety. 5.3 Noise pollution: The noise pollution caused by the vibration of gate valves cannot be ignored. Vibration causes the internal components of the gate valve to collide and rub against each other, and it also leads to turbulence and eddies in the fluid within the valve, all of which generate harsh noises. Such noise not only disrupts the working environment around it and affects the hearing as well as the physical and mental health of workers, but it can also cause noise pollution in the lives of residents living in the vicinity. Prolonged noise pollution can cause negative emotions such as irritability and anxiety, reduce work efficiency and quality of life, and may even lead to noise-related occupational diseases, posing a serious threat to people’s physical and mental health. VI. Measures to Prevent and Resolve Vibration in Gate Valves 6.1 Proper Selection and Operation The selection and operation of gate valves are crucial; if flow regulation is required, globe valves or control valves should be used, as they have an S-shaped flow channel and good guiding properties, making them more suitable for throttling applications. Avoid throttling using gate valves to prevent severe vibrations and damage caused by throttling. When a gate valve is operated at a position close to fully open (e.g., with an opening degree of over 80%) or fully closed, the gate plate has its greatest cantilever length and lowest rigidity when it is partially open, making it susceptible to vibration caused by fluid impacts. At low opening degrees, throttling is severe; the fluid exerts a large force on the gate, causing intense vortices that can easily lead to resonance. Proper selection and operation can fundamentally reduce the vibration of gate valves, ensure their stable operation, extend their service life, prevent various hazards caused by vibration, and guarantee the safe and efficient transfer of fluids within the pipeline system. 6.2 Optimizing system design: Optimizing the system design can effectively prevent vibration in gate valves. By appropriately increasing the pipe diameter to reduce the flow velocity of the medium, high-speed fluids tend to generate intense turbulence and vortices, exerting large forces on the gate plate; increasing the pipe diameter can improve the flow pattern and reduce vibration sources. Increasing pipe support is also crucial; installing reliable brackets or clamps near the valves can enhance the stiffness of the system and change its resonance frequency. When the pipeline is properly supported, it is possible to effectively prevent pipeline vibrations from being transmitted to the gate valve, thus avoiding resonance in the gate valve caused by those vibrations. This allows the gate valve to operate in a stable environment, reduces the impact of vibrations on its structural strength and sealing performance, and ensures the overall safety and stability of the pipeline system. 6.3 Use of improved gate valves: Improved gate valves play a significant role in preventing vibration in these valves. The gate of the elastic seat seal gate valve is fully covered with a rubber coating, which enables it to absorb vibration energy. When fluid impacts the gate and causes vibrations, this rubber coating acts like a shock absorber, reducing the impact of those vibrations on the gate. Gate valves with flow guide holes feature these holes on the gate plate, which help to improve the flow pattern. This results in a smoother flow of fluid through the valve, reduces the formation of vortices, and decreases the alternating lift force exerted by Karman vortices on the gate plate, thereby reducing vibration of the gate plate. These improved gate valves are structurally optimized over traditional gate valves, enabling them to better cope with complex operating conditions, reducing the risk of vibration, and enhancing the performance and reliability of the gate valves. 6.4 On-site treatment measures When the gate valve vibrates, on-site treatment measures can be taken. If vibration is detected, try adjusting the operating position by slightly opening or closing the valve, thereby changing the flow conditions and the frequency of forces acting on the gate, in order to avoid the resonance point and ensure stable operation of the gate valve. It is also necessary to check whether the pipe supports and valve connection bolts are loose, and tighten them promptly. Loose pipe supports can exacerbate vibrations, while loose bolts can affect the structural stability of the gate valve. Through these simple on-site treatments, the vibration of gate valves can be effectively reduced, ensuring their proper operation and preventing more serious failures caused by vibration.