10 frequently encountered problems in valve use 1, why double seat valve easy to oscillate when working? For single core, when the medium is open type, the valve stability is good; when the medium is flow closed, the valve stability is poor. Double-seated valve has two spools, the lower spool in the flow closed, the valve spool is open, so that work in a small opening, the flow-closure valve spool is easy to cause the valve vibration, which is double seat valve Can not be used for a small degree of work reason. 2, why double seal valve can not be used as a shut-off valve? The advantages of two-seater valve spool force balance structure, allowing pressure, but it highlights the shortcomings of the two sealing surfaces can not be a good contact at the same time, resulting in a large leak. If it is artificially and purposely used to cut the occasion, apparently ineffective, even for it made many improvements (such as double seal sleeve valve), is not desirable. 3, what is the difference between the straight-stroke adjustment valve anti-blocking performance, anti-blocking valve performance good? Straight stroke valve spool is a vertical throttling, and the medium is the level of flow in and out of the valve cavity flow path must turn around the flip, so that the valve flow path becomes quite complex (the shape of the inverted "S" type). such, 4, why the straight stroke regulator valve stem thin? It involves a simple mechanical principle: large sliding friction, small rolling friction. Straight travel valve stem up and down movement, a little tight packing, it will be very tight stem package, resulting in greater backlash. To this end, the valve stem is designed to be very small, packing and PTFE friction coefficient is often small PTFE packing, in order to reduce backlash, but the problem is sent stem thin, easy to bend, filler life is short. Solve this problem, the best way is to travel with the valve stem, which is the type of angular travel control valve, the valve stem than the straight travel valve stem thick 2 to 3 times, and the choice of long life graphite packing, stem stiffness Good, long filler life, but the friction torque on the contrary, small backlash. 5, why the angular stroke valve cut off the larger pressure? Angle stroke valve to cut off the larger pressure differential is because the media in the valve core or valve plate together on the torque generated by the rotating shaft is very small, therefore, it can withstand greater pressure. 6, why the desalted water medium using rubber lined butterfly valve lined diaphragm valve life is short? Desalinated water medium contains a low concentration of acid or alkali, they are more corrosive to rubber. Rubber is corrosive performance of expansion, aging, low strength, with rubber lining butterfly valve, diaphragm valve are poor, the effect is not rubber corrosion. Liner rubber diaphragm valve improved corrosion-resistant performance of fluorine-lined diaphragm valve, but lined with fluorine diaphragm valve can not withstand the collapse of the upper and lower folded, resulting in mechanical damage, valve life shorter. Now the best way is to use special ball valve water treatment, it can be used to 5 to 8 years. 7, why cut-off valve should try hard seal? Shut-off valve requires a lower leakage as possible, the leakage of soft-sealed valve is the lowest, of course, cut off the effect, but not wear-resistant, poor reliability. From the leakage is small, sealed and reliable double standards, the soft seal cut off as good as the hard seal cut off. Such as full-function ultra-light control valve, sealed and piled with wear-resistant alloy protection, high reliability, leakage rate of 10-7, has been able to meet the requirements of shut-off valve. 8, why the sleeve valve instead of single, double seat valve but did not get it? Sleeve valves were introduced in the 1960s. They were widely used in the 1970s at home and abroad. In the 1980s, the percentage of sleeve valves in petrochemical plants was large. At that time, many people thought that sleeve valves could replace single and double seat valves , Become the second generation product. Until now, not so, single-seat valve, seat valve, sleeve valve are the same use. This is because the sleeve valve is only improved throttle mode, stability and maintenance better than a single seat valve, but its weight, anti-blocking and leakage indicators with the single, double seat valve, how can it replace single, double seat valve What? So, can only be used together. 9, why selection is more important than calculating? Calculation and selection comparison, the selection is much more important, much more complex. Because calculation is just a simple formula calculation, it does not depend on the accuracy of the formula itself, but on the accuracy of the given process parameters. Selection involves more content, a little careless, it will lead to improper selection, not only cause manpower, material resources, financial 10, why the piston actuator in the pneumatic valve will be more and more? For pneumatic valves, the piston actuator can take full advantage of the air pressure, the actuator size smaller than the film, the thrust greater piston in the O-ring is also more reliable than the film, so its use will be more and more many. Procurement before the valve selection steps and based on: In fluid piping systems, valves are control elements whose primary function is to isolate equipment and piping, regulate flow, and prevent back pressure, regulation, and drain pressure. It is also important to understand the characteristics of the valve and the procedure and rationale for selecting the valve, since it is important to choose the most suitable valve for the piping system. The valve industry so far has been able to produce a full range of gate, globe, throttle, plug, ball, electric, diaphragm, check, safety, pressure, steam trap and emergency shut-off valves And other 12 categories, more than 3,000 models, more than 4,000 specifications of the valve products; maximum working pressure of 600MPa, the maximum nominal diameter of 5350mm, the maximum operating temperature of 1200 ℃, the minimum operating temperature of -196 ℃, the media for the water , Steam, oil, natural gas, corrosive media such as concentrated nitric acid, medium concentration sulfuric acid, flammable media (such as stupid and ethylene), toxic media (such as hydrogen sulfide), explosive media and radioactive media Metal sodium, - loop pure water, etc.). Valve pressure parts made of cast copper, cast iron, ductile iron, high silicon cast iron, cast steel, forged steel, high and low alloy steel, stainless steel, Hastelloy, Inconel, Monel, duplex stainless steel , Titanium alloy and so on. And can produce all kinds of electric, pneumatic, hydraulic valve drive. In the face of so many valve varieties and so complicated a variety of conditions, to choose the most suitable piping system installed valve products, I think, should first understand the characteristics of the valve; secondly, should grasp the choice of the valve steps and basis; Follow the principle of choosing a valve. The valve industry so far has been able to produce a full range of gate, globe, throttle, plug, ball, electric, diaphragm, check, safety, pressure, steam trap and emergency shut-off valves And other 12 categories, more than 3,000 models, more than 4,000 specifications of the valve products; maximum working pressure of 600MPa, the maximum nominal diameter of 5350mm, the maximum operating temperature of 1200 ℃, the minimum operating temperature of -196 ℃, the media for the water , Steam, oil, natural gas, corrosive media such as concentrated nitric acid, medium concentration sulfuric acid, flammable media (such as stupid and ethylene), toxic media (such as hydrogen sulfide), explosive media and radioactive media Metal sodium, - loop pure water, etc.). Valve pressure parts made of cast copper, cast iron, ductile iron, high silicon cast iron, cast steel, forged steel, high and low alloy steel, stainless steel, Hastelloy, Inconel, Monel, duplex stainless steel , Titanium alloy and so on. And can produce all kinds of electric, pneumatic, hydraulic valve drive. In the face of so many valve varieties and so complicated a variety of conditions, to choose the most suitable piping system installed valve products, I think, should first understand the characteristics of the valve; secondly, should grasp the choice of the valve steps and basis; Follow the principle of choosing a valve. 1. There are two general characteristics of the valve, the use of features and structural characteristics. Features: It determines the main use of the valve performance and scope of use, the use of the valve characteristics are: the type of valve (closed circuit valves, regulating valves, safety valves, etc.); product type (gate valve, globe valve, butterfly valve, ball valve, etc.) ; Valve main components (body, bonnet, valve stem, valve flap, sealing surface) of the material; valve transmission and so on. Structural characteristics: It determines the valve installation, repair, maintenance and other methods of some of the structural characteristics of the structural characteristics are: the length of the valve structure and the overall height of the connection with the pipeline (flange connection, screw connection, clamp connection , External thread connection, welding end connection, etc.); sealing surface form (set ring, thread ring, surfacing, spray welding, valve body); Stem structure (rotary rod, lifting rod) and so on. Select the valve steps and based on the following general: (1) select steps 1 clear the valve in the device or device uses to determine the working conditions of the valve: the medium, working pressure, working temperature and so on. 2. Determine the nominal diameter and connection of the pipeline connecting the valve: flange, thread, welding and so on. 3. Determine the way to operate the valve: manual, electric, electromagnetic, pneumatic or hydraulic, electrical linkage or electro-hydraulic linkage. 4. According to the pipeline transportation medium, working pressure, working temperature to determine the selected valve shell and inner parts of the material: gray cast iron, ductile iron, ductile iron, carbon steel, alloy steel, stainless steel, copper alloy. 5. Determine the type of valve: gate valve, globe valve, ball valve, butterfly valve, throttle, safety valve, pressure reducing valve, steam trap, and so on. 6. Determine the valve parameters: For automatic valves, according to the different needs of the first to allow flow resistance, discharge capacity, back pressure, etc., and then determine the nominal diameter of the pipe and seat hole diameter. 7. Determine the geometry of the selected valve geometry: the length of the structure, the form and size of the flange connection, opening and closing the size of the valve height direction, the size and number of bolt holes connected to the entire valve dimensions and so on. 8. Use existing information: valve product catalog, valve product samples to choose the right valve products. ⑵ based on the choice of valve In understanding the steps to choose the valve at the same time, but also to learn more about the basis for the selection of the valve. 1. The choice of the use of the valve, the use conditions and operating conditions control mode. 2. The nature of the working medium: working pressure, working temperature, corrosion performance, whether it contains solid particles, the media is toxic, whether it is flammable, explosive media, medium viscosity and so on. 3 on the valve fluid characteristics of the requirements: flow resistance, emission capacity, flow characteristics, sealing grade and so on. 4. Installation dimensions and dimensions requirements: nominal diameter, pipe connections and connection dimensions, dimensions or weight restrictions. ⑤ on the valve product reliability, service life and explosion-proof performance of electric devices and other additional requirements. (When selecting a parameter, note the following additional parameters if the valve is to be used for control purposes: method of operation, maximum and minimum flow requirements, pressure drop for normal flow, pressure drop when closed, maximum and minimum inlet of valve Pressure.) Based on the basis and procedure for choosing a valve, the proper and correct selection of the valve must also be followed by a detailed understanding of the internal structure of the various types of valve so that the correct choice of the preferred valve can be made. The ultimate control of the pipeline is the valve. Valve opening and closing pieces control the flow of medium in the pipeline, the shape of the valve flow path to the valve with a certain flow characteristics in the choice of the most suitable piping system to install the valve must take into account this point. 3. The following principles should be followed to select the valve: ⑴ cut off and open the medium valve flow path for the straight-through valve, the flow resistance is small, usually selected as the cut-off and open media valve. Closed-down valve (globe valve, piston valve) because of its tortuous flow, flow resistance than other valves, it is less choice. In the case of allowing higher flow resistance, the choice of closed valve. ⑵ control flow with the valve usually choose to easily adjust the flow of the valve as a control flow. Closed-down valves, such as stop valves, are suitable for this purpose because their seat size is proportional to the travel of the closure. Rotary valves (plug valves, butterfly valves, ball valves) and flexible valve bodies (pinch valves, diaphragm valves) can also be used for throttling control, but usually only for a limited range of valve diameters. Gate valve is a disc-shaped gate of the circular valve seat to make cross-sectional movement, it only close to the closed position, in order to better control the flow, it is not usually used for flow control. 2. The nature of the working medium: working pressure, working temperature, corrosion performance, whether it contains solid particles, the media is toxic, whether it is flammable, explosive media, medium viscosity and so on. 3 on the valve fluid characteristics of the requirements: flow resistance, emission capacity, flow characteristics, sealing grade and so on. 4. Installation dimensions and dimensions requirements: nominal diameter, pipe connections and connection dimensions, dimensions or weight restrictions. ⑤ on the valve product reliability, service life and explosion-proof performance of electric devices and other additional requirements. (When selecting a parameter, note the following additional parameters if the valve is to be used for control purposes: method of operation, maximum and minimum flow requirements, pressure drop for normal flow, pressure drop when closed, maximum and minimum inlet of valve Pressure.) Based on the basis and procedure for choosing a valve, the proper and correct selection of the valve must also be followed by a detailed understanding of the internal structure of the various types of valve so that the correct choice of the preferred valve can be made. The ultimate control of the pipeline is the valve. Valve opening and closing pieces control the flow of medium in the pipeline, the shape of the valve flow path to the valve with a certain flow characteristics in the choice of the most suitable piping system to install the valve must take into account this point. 3. The following principles should be followed to select the valve: ⑴ cut off and open the medium valve flow path for the straight-through valve, the flow resistance is small, usually selected as the cut-off and open media valve. Closed-down valve (globe valve, piston valve) because of its tortuous flow, flow resistance than other valves, it is less choice. In the case of allowing higher flow resistance, the choice of closed valve. ⑵ control flow with the valve usually choose to easily adjust the flow of the valve as a control flow. Closed-down valves, such as stop valves, are suitable for this purpose because their seat size is proportional to the travel of the closure. Rotary valves (plug valves, butterfly valves, ball valves) and flexible valve bodies (pinch valves, diaphragm valves) can also be used for throttling control, but usually only for a limited range of valve diameters. Gate valve is a disc-shaped gate of the circular valve seat to make cross-sectional movement, it only close to the closed position, in order to better control the flow, it is not usually used for flow control. Valve check the main content 1, the valve stem seals and flange gasket static seal leaks 2, open and close the state is normal 3, the valve body damage and leakage and other anomalies 4, the normally open or normally closed valve rotation 1 ~ 2 laps or make a lift test 5, the normally open or normally closed valve stem parts lubrication 6, check and debug the pneumatic valve power head and electrical system Ps Foam Cutting Machine,Hot Wire Cnc Foam Cutting Machines,Foam Cutting Machine Cnc,Industrial Foam Cutting Machine haiyuanmachinery , https://www.hyfoambox.com
Hand teach you the selection of the valve, maintenance and repair
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