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2022

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my country launches high-temperature paper safety material sprue tube, paper fire is also "compatible"

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In fluid pipeline systems, valves are control components whose main functions are to isolate equipment and pipeline systems, regulate flow, prevent backflow, regulate and relieve pressure. Since it is very important to select the most suitable valve for the pipeline system, it is also important to understand the characteristics of the valve and the steps and basis for selecting the valve.

So far, the valve industry has been able to produce a full range of gate valves, globe valves, throttle valves, plug valves, ball valves, electric valves, diaphragm valves, check valves, safety valves, pressure reducing valves, steam traps and emergency shut-off valves. Valve products in 12 categories, more than 3,000 models, and more than 4,000 specifications; **** working pressure is 600MPa, **** nominal diameter reaches 5350mm, **** working temperature is 1200°C, *** *The working temperature is -196°C, and the applicable media are water, steam, oil, natural gas, highly corrosive media (such as concentrated nitric acid, medium-concentration sulfuric acid, etc.), flammable media (such as benzene, ethylene, etc.), toxic media (such as Hydrogen sulfide), explosive media and radioactive media (metal sodium, - loop pure water, etc.).

Valve pressure-bearing parts are made of cast copper, cast iron, ductile iron, high silicon cast iron, cast steel, forged steel, high and low alloy steel, stainless acid-resistant steel, Hastelloy, Inconel, Monel, duplex stainless steel , titanium alloy, etc. And can produce various electric, pneumatic and hydraulic valve driving devices. Faced with so many types of valves and such complex working conditions, in order to choose the most suitable valve product for installation in the pipeline system, I believe that you should first understand the characteristics of the valve; secondly, you should master the steps and basis for selecting the valve; thirdly The principles for selecting valves should be followed.

1. There are generally two types of valve characteristics, usage characteristics and structural characteristics.

Usage characteristics: It determines the main performance and scope of use of the valve. The usage characteristics of the valve include: valve category (closed-circuit valve, regulating valve, safety valve, etc.); product type (gate valve, globe valve, butterfly valve, ball valve, etc.) ; Materials of the main parts of the valve (valve body, valve cover, valve stem, valve disc, sealing surface); valve transmission mode, etc. Structural characteristics: It determines some structural characteristics of the valve installation, repair, maintenance and other methods. The structural characteristics include: the structural length and overall height of the valve, the connection form with the pipeline (flange connection, threaded connection, clamp connection , external thread connection, welded end connection, etc.); the form of the sealing surface (inlaid ring, threaded ring, overlay welding, spray welding, valve body); the valve stem structural form (rotating rod, lifting rod), etc.

2. The steps and basis for selecting valves are generally as follows:

⑴Select steps

1. Clarify the purpose of the valve in the equipment or device, and determine the working conditions of the valve: applicable medium, working pressure, working temperature, etc.

2. Determine the nominal diameter and connection method of the pipe connected to the valve: flange, thread, welding, etc.

3. Determine the method of operating the valve: manual, electric, electromagnetic, pneumatic or hydraulic, electrical linkage or electro-hydraulic linkage, etc.

4. Determine the materials of the selected valve shell and internal parts based on the medium transported by the pipeline, working pressure, and working temperature: gray cast iron, malleable cast iron, ductile iron, carbon steel, alloy steel, stainless acid-resistant steel, copper alloy, etc.

5. Determine the type of valve: gate valve, globe valve, ball valve, butterfly valve, throttle valve, safety valve, pressure reducing valve, steam trap, etc.

6. Determine the parameters of the valve: For automatic valves, first determine the allowable flow resistance, discharge capacity, back pressure, etc. according to different needs, and then determine the nominal diameter of the pipeline and the diameter of the valve seat hole.

7. Determine the geometric parameters of the selected valve: structural length, flange connection form and size, height dimension of the valve after opening and closing, size and number of connecting bolt holes, overall valve appearance dimensions, etc.

8. Use existing information: valve product catalogs, valve product samples, etc. to select appropriate valve products.

⑵ Basis for selecting valves. While understanding and mastering the steps for selecting valves, you should also further understand the basis for selecting valves.

1. The purpose, operating conditions and operation control method of the selected valve.

2. The nature of the working medium: working pressure, working temperature, corrosion performance, whether it contains solid particles, whether the medium is toxic, whether it is a flammable or explosive medium, the viscosity of the medium, etc.

3. Requirements for valve fluid characteristics: flow resistance, discharge capacity, flow characteristics, sealing grade, etc.

4. Installation dimensions and overall dimension requirements: nominal diameter, connection method and connection size to the pipeline, overall dimensions or weight limit, etc. ⑤Additional requirements for the reliability, service life of valve products and the explosion-proof performance of electric devices. (Note when selecting parameters: If the valve is to be used for control purposes, the following additional parameters must be determined: operating method, minimum and minimum flow requirements, pressure drop for normal flow, pressure drop when closed, valve ** and **minimum inlet pressure.) According to the above-mentioned basis and steps for selecting valves, when selecting valves reasonably and correctly, you must also have a detailed understanding of the internal structures of various types of valves, so that you can prioritize the valves. Make the right decision. The final control of the pipeline is the valve. The valve opening and closing parts control the flow pattern of the medium in the pipeline. The shape of the valve flow channel gives the valve certain flow characteristics. This must be taken into consideration when selecting the most suitable valve for installation in the pipeline system.

3. The following are the principles that should be followed when selecting valves:

⑴Valves used to cut off and open the medium. The flow path of the valve is a straight-through valve, which has a small flow resistance. It is usually selected as a valve for cutting off and opening the medium. Downward closing valves (stop valves, plunger valves) are rarely used due to their tortuous flow paths and higher flow resistance than other valves. In situations where higher flow resistance is allowed, closed valves can be selected.

⑵The valve used to control the flow is usually a valve that is easy to adjust the flow. Downward-closing valves (such as globe valves) are suitable for this purpose because their seat size is directly proportional to the stroke of the closing member. Rotary valves (plug valves, butterfly valves, ball valves) and deflection valves (pinch valves, diaphragm valves) can also be used for throttling control, but usually only within a limited valve diameter range. The gate valve uses a disc-shaped gate plate to make a transverse movement to the circular valve seat opening. It can better control the flow only when it is close to the closed position, so it is usually not used for flow control.

⑶ Valve for reversing and shunting. According to the needs of reversing and shunting, this valve can have three or more channels. Plug valves and ball valves are more suitable for this purpose. Therefore, most valves used for reversing and diverting flow choose one of these types of valves. However, in some cases, other types of valves can also be used for reversing and diverting flow as long as two or more valves are properly connected to each other.

⑷Valves for media with suspended particles. When the medium contains suspended particles, it is most suitable to use a valve with a wiping effect that the closing part slides along the sealing surface. If the back-and-forth movement of the closing member against the valve seat is vertical, particles may be trapped. Therefore, this type of valve is only suitable for basically clean media unless the sealing surface material can allow embedded particles. Ball valves and plug valves have a wiping effect on the sealing surface during the opening and closing process, so they are suitable for use in media with suspended particles. At present, whether in the pipeline system of petroleum, chemical industry, or other industries, the application, operating frequency and service of valves are ever-changing. To control or eliminate even small leaks, the most important and critical equipment is the valve. The ultimate control of the pipeline is the valve, which is unique in its service and reliable performance in various fields.

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In fluid pipeline systems, valves are control components whose main functions are to isolate equipment and pipeline systems, regulate flow, prevent backflow, regulate and relieve pressure. Since it is very important to select the most suitable valve for the pipeline system, it is also important to understand the characteristics of the valve and the steps and basis for selecting the valve.

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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 closed and the upper valve core is open. In this way, when working at a small opening, the closed-flow valve core will easily cause vibration of the valve. This is a double-seat valve. The reason why it cannot be used for small opening work.

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